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• How to backup data from linux servers to linux server (incremental + snapshot)?

  - by wag2639

  We have a handful of hosted servers running RHEL4 and RHEL5 and would like to backup some key folders (I'm thinking /var /srv and /etc) to a local server we have in house. The local server is running Ubuntu 9.10 Server edition. I'm looking for a free (preferably OSS) way to grab (or push) incremental backups to my local server and once a month or so, make a new snapshot for incremental updates in between snapshots. Also, while I'm comfortable with using a command line, others may need to use the system in the future, and I would like some kind of graphical or web interface to browse the backup repository. Suggestions?

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• Practical way of keeping up-to-date backup servers?

  - by ftkg

  What is the approach generally used when you want to have backup physical servers? Currently I have a Linux server running a database, a samba share, a webapp and some scripts; and a Windows Server, running some third-party software. What I would like was to be able to have a ready backup server to enter in production in case of failure, but how to keep them up-to-date? I've seen some expensive solutions for Windows; for Linux I've wondered if I really have to build an array of scripts.

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• Two SSL certificates required for two Apache servers using mod_proxy to serve HTTPS?

  - by Nick

  Our application originally used a single Apache server with mod_perl installed to serve up all HTTPS requests. Due to memory issues I've added a lighter Apache installation and used ProxyPass to hand off the Perl requests to the mod_perl enabled server. We currently have an SSL certificate installed on the mod_perl server but I'm struggling to understand whether we need a certificate for both servers or only the lightweight server which is receiving the original requests. Or can a certificate be used for more than one server on a single machine? Thanks in advance for any help/pointers.

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• Setting up VPS hosting

  - by RobinFTW

  I'm trying to set up my own vps hosting. It wont be a paid service, just an experiment for me and some nerdy friends. What I'd like to be able to do is this: Run multiple virtual servers on 1 external IP. These servers can run anything from Minecraft servers to simple http servers. They will also need to be accessible thru SSH. What I don't get is how I can address these servers using domain names. I've done some research and found out that I could use Vhosts with Apache. However this only applies to http servers. It was also suggested I'd use a reverse proxy(squid) but this also only applies to http requests. I could just use different ports for different servers, but thats not ideal and not what I want. Can someone suggest a setup? Maybe some tutorials or anything.

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• upgrading servers, need to keep domain same as before. what are the best practices?

  - by nLL

  Hi, I am upgrading a domain controller/file server from win2003 standard to win2008 r2 standard. We are planing to have a file server and an AD controller. Our old hardware will be scrapped, we want to copy all AD users/computers to new machine and keep current domain name. I never done this before. What are the best practices? Is it better if we get a contractor to do it for us? I guess best way to start is to build new servers, copy data, take old server down and put new server online. My gut says we would need to re-join all computers. Is that correct? Any input appreciated.

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• solutions for a webserver dedicated to manage permissions/ACL and (reverse) proxying API servers?

  - by giohappy

  I'm considering various layouts to expose various HTTP API services (running on their own differents servers) through a frontend server dedicated to manage permissions on behalf of the API services. I've considered various options, from the classical ones like Nginx, Apache, etc. to HAProxy, passing by the various Python webserver solutions like Tornado, Twisted (which gives me the opportunity to implement my own ACL system easily). The foundamental feature is high performance and scalability, and the ability to manage fine grained ACL rules (similar to the HAProxy ACL system) I would like to know what is a suggested approach to setup what I need, and if (opne source) ready-to-use solutions are already available dedicated to this.

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• Methods of sending web-generated config files to servers and restarting services.

  - by JPG

  Hi, We're writing a web-based tool to configure our services provided by multiple servers. This includes interfaces configuration, dhcp configs etc. etc. Having configs in database and views that generate proper output, how to send it/make it available for servers? I'm thinking about sending it through scp and invoking reload command to services through ssh. I'm also thinking about using Func to do all the job, as this is Python tool and will seemingly integrate with python-based (django) config tool. Any other proposals?

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• What is a realistic average time difference between servers in the same LAN?

  - by monster

  Until recently, we had at work a small cluster of about 20 small Windows servers (which have now all been virtualized). They were all configured to synchronize with the local time server. It was on an 1Gb sub-network in our own DC. I never got them to be less than about 100ms away from each other, which I consider to be an incredibly big difference. Is that a normal value? What is a realistic expectation of time difference between machines running on a 1Gb network, and all connected to the same time server, and updating frequently, say every 5 minutes? I would like to know this as setting timeouts and other parameters in a distributed application requires to take that difference into consideration.

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• Is there a good way to prevent a server from emailing a specific address (we control both servers/apps)?

  - by Bms85smb

  When testing a production app we occasionally need to pull from a live site and perform tests on a development server. There are quite a few email addresses stored in the database that we need to modify every time we restore to the development server. Occasionally someone on my team will miss one and accidentally send an email through the distribution list. The email looks legit because it is coming from a clone, it can cause quite the situation. We have a protocol we follow every time we clone the live app and it has helped a lot but I would feel better if it was impossible for the two servers to communicate. Is there a good way to do this? Can firewall rules block email? Does Plesk have a blacklist?

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• Juju Zookeeper & Provisioning Agent Not Deployed

  - by Keith Tobin

  I am using juju with the openstack provider, i expected that when i bootstrap that zookeeper and provisioning agent would get deployed on the bootstrap vm in openstack. This dose not seem to be the case. the bootstrap vm gets deployed but it seems that nothing gets deployed to the VM. See logs below, I may be missing something, also how is it possible to log on the bootstrap vm. Could I manual deploy, if so what do I need to do. Juju Bootstrap commend root@cinder01:/home/cinder# juju -v bootstrap 2012-10-12 03:21:20,976 DEBUG Initializing juju bootstrap runtime 2012-10-12 03:21:20,982 WARNING Verification of xxxxS certificates is disabled for this environment. Set 'ssl-hostname-verification' to ensure secure communication. 2012-10-12 03:21:20,982 DEBUG openstack: using auth-mode 'userpass' with xxxx:xxxxxx.10:35357/v2.0/ 2012-10-12 03:21:21,064 DEBUG openstack: authenticated til u'2012-10-13T08:21:13Z' 2012-10-12 03:21:21,064 DEBUG openstack: GET 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors' 2012-10-12 03:21:21,091 DEBUG openstack: 200 '{"flavors": [{"id": "3", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/3", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/3", "rel": "bookmark"}], "name": "m1.medium"}, {"id": "4", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/4", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/4", "rel": "bookmark"}], "name": "m1.large"}, {"id": "1", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/1", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/1", "rel": "bookmark"}], "name": "m1.tiny"}, {"id": "5", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/5", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/5", "rel": "bookmark"}], "name": "m1.xlarge"}, {"id": "2", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/2", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/2", "rel": "bookmark"}], "name": "m1.small"}]}' 2012-10-12 03:21:21,091 INFO Bootstrapping environment 'openstack' (origin: ppa type: openstack)... 2012-10-12 03:21:21,091 DEBUG access object-store @ xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/provider-state 2012-10-12 03:21:21,092 DEBUG openstack: GET 'xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/provider-state' 2012-10-12 03:21:21,165 DEBUG openstack: 200 '{}\n' 2012-10-12 03:21:21,165 DEBUG Verifying writable storage 2012-10-12 03:21:21,165 DEBUG access object-store @ xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/bootstrap-verify 2012-10-12 03:21:21,166 DEBUG openstack: PUT 'xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/bootstrap-verify' 2012-10-12 03:21:21,251 DEBUG openstack: 201 '201 Created\n\n\n\n ' 2012-10-12 03:21:21,251 DEBUG Launching juju bootstrap instance. 2012-10-12 03:21:21,271 DEBUG access object-store @ xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/juju_master_id 2012-10-12 03:21:21,273 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-groups 2012-10-12 03:21:21,273 DEBUG openstack: GET 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-groups' 2012-10-12 03:21:21,321 DEBUG openstack: 200 '{"security_groups": [{"rules": [{"from_port": -1, "group": {}, "ip_protocol": "icmp", "to_port": -1, "parent_group_id": 1, "ip_range": {"cidr": "0.0.0.0/0"}, "id": 7}, {"from_port": 22, "group": {}, "ip_protocol": "tcp", "to_port": 22, "parent_group_id": 1, "ip_range": {"cidr": "0.0.0.0/0"}, "id": 38}], "tenant_id": "d5f52673953f49e595279e89ddde979d", "id": 1, "name": "default", "description": "default"}]}' 2012-10-12 03:21:21,322 DEBUG Creating juju security group juju-openstack 2012-10-12 03:21:21,322 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-groups' 2012-10-12 03:21:21,401 DEBUG openstack: 200 '{"security_group": {"rules": [], "tenant_id": "d5f52673953f49e595279e89ddde979d", "id": 48, "name": "juju-openstack", "description": "juju group for openstack"}}' 2012-10-12 03:21:21,401 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-group-rules' 2012-10-12 03:21:21,504 DEBUG openstack: 200 '{"security_group_rule": {"from_port": 22, "group": {}, "ip_protocol": "tcp", "to_port": 22, "parent_group_id": 48, "ip_range": {"cidr": "0.0.0.0/0"}, "id": 54}}' 2012-10-12 03:21:21,504 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-group-rules' 2012-10-12 03:21:21,647 DEBUG openstack: 200 '{"security_group_rule": {"from_port": 1, "group": {"tenant_id": "d5f52673953f49e595279e89ddde979d", "name": "juju-openstack"}, "ip_protocol": "tcp", "to_port": 65535, "parent_group_id": 48, "ip_range": {}, "id": 55}}' 2012-10-12 03:21:21,647 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-group-rules' 2012-10-12 03:21:21,791 DEBUG openstack: 200 '{"security_group_rule": {"from_port": 1, "group": {"tenant_id": "d5f52673953f49e595279e89ddde979d", "name": "juju-openstack"}, "ip_protocol": "udp", "to_port": 65535, "parent_group_id": 48, "ip_range": {}, "id": 56}}' 2012-10-12 03:21:21,792 DEBUG Creating machine security group juju-openstack-0 2012-10-12 03:21:21,792 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-security-groups' 2012-10-12 03:21:21,871 DEBUG openstack: 200 '{"security_group": {"rules": [], "tenant_id": "d5f52673953f49e595279e89ddde979d", "id": 49, "name": "juju-openstack-0", "description": "juju group for openstack machine 0"}}' 2012-10-12 03:21:21,871 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/detail 2012-10-12 03:21:21,871 DEBUG openstack: GET 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/detail' 2012-10-12 03:21:21,906 DEBUG openstack: 200 '{"flavors": [{"vcpus": 2, "disk": 10, "name": "m1.medium", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/3", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/3", "rel": "bookmark"}], "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 40, "ram": 4096, "id": "3", "swap": ""}, {"vcpus": 4, "disk": 10, "name": "m1.large", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/4", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/4", "rel": "bookmark"}], "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 80, "ram": 8192, "id": "4", "swap": ""}, {"vcpus": 1, "disk": 0, "name": "m1.tiny", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/1", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/1", "rel": "bookmark"}], "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "ram": 512, "id": "1", "swap": ""}, {"vcpus": 8, "disk": 10, "name": "m1.xlarge", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/5", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/5", "rel": "bookmark"}], "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 160, "ram": 16384, "id": "5", "swap": ""}, {"vcpus": 1, "disk": 10, "name": "m1.small", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/flavors/2", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/2", "rel": "bookmark"}], "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 20, "ram": 2048, "id": "2", "swap": ""}]}' 2012-10-12 03:21:21,907 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers 2012-10-12 03:21:21,907 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers' 2012-10-12 03:21:22,284 DEBUG openstack: 202 '{"server": {"OS-DCF:diskConfig": "MANUAL", "id": "a598b402-8678-4447-baeb-59255409a023", "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023", "rel": "bookmark"}], "adminPass": "SuFp48cZzdo4"}}' 2012-10-12 03:21:22,284 DEBUG access object-store @ xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/juju_master_id 2012-10-12 03:21:22,285 DEBUG openstack: PUT 'xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/juju_master_id' 2012-10-12 03:21:22,375 DEBUG openstack: 201 '201 Created\n\n\n\n ' 2012-10-12 03:21:27,379 DEBUG Waited for 5 seconds for networking on server u'a598b402-8678-4447-baeb-59255409a023' 2012-10-12 03:21:27,380 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023 2012-10-12 03:21:27,380 DEBUG openstack: GET 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023' 2012-10-12 03:21:27,556 DEBUG openstack: 200 '{"server": {"OS-EXT-STS:task_state": "networking", "addresses": {"private": [{"version": 4, "addr": "10.0.0.8"}]}, "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023", "rel": "bookmark"}], "image": {"id": "5bf60467-0136-4471-9818-e13ade75a0a1", "links": [{"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/images/5bf60467-0136-4471-9818-e13ade75a0a1", "rel": "bookmark"}]}, "OS-EXT-STS:vm_state": "building", "OS-EXT-SRV-ATTR:instance_name": "instance-00000060", "flavor": {"id": "1", "links": [{"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/1", "rel": "bookmark"}]}, "id": "a598b402-8678-4447-baeb-59255409a023", "user_id": "01610f73d0fb4922aefff09f2627e50c", "OS-DCF:diskConfig": "MANUAL", "accessIPv4": "", "accessIPv6": "", "progress": 0, "OS-EXT-STS:power_state": 0, "config_drive": "", "status": "BUILD", "updated": "2012-10-12T08:21:23Z", "hostId": "1cdb25708fb8e464d83a69fe4a024dcd5a80baf24a82ec28f9d9f866", "OS-EXT-SRV-ATTR:host": "nova01", "key_name": "", "OS-EXT-SRV-ATTR:hypervisor_hostname": null, "name": "juju openstack instance 0", "created": "2012-10-12T08:21:22Z", "tenant_id": "d5f52673953f49e595279e89ddde979d", "metadata": {}}}' 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 2012-10-12 03:21:27,557 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-floating-ips 2012-10-12 03:21:27,557 DEBUG openstack: GET 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/os-floating-ips' 2012-10-12 03:21:27,815 DEBUG openstack: 200 '{"floating_ips": [{"instance_id": "a0e0df11-91c0-4801-95b3-62d910d729e9", "ip": "xxxx.35", "fixed_ip": "10.0.0.5", "id": 447, "pool": "nova"}, {"instance_id": "b84f1a42-7192-415e-8650-ebb1aa56e97f", "ip": "xxxx.36", "fixed_ip": "10.0.0.6", "id": 448, "pool": "nova"}, {"instance_id": null, "ip": "xxxx.37", "fixed_ip": null, "id": 449, "pool": "nova"}, {"instance_id": null, "ip": "xxxx.38", "fixed_ip": null, "id": 450, "pool": "nova"}, {"instance_id": null, "ip": "xxxx.39", "fixed_ip": null, "id": 451, "pool": "nova"}, {"instance_id": null, "ip": "xxxx.40", "fixed_ip": null, "id": 452, "pool": "nova"}, {"instance_id": null, "ip": "xxxx.41", "fixed_ip": null, "id": 453, "pool": "nova"}]}' 2012-10-12 03:21:27,815 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023/action 2012-10-12 03:21:27,816 DEBUG openstack: POST 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023/action' 2012-10-12 03:21:28,356 DEBUG openstack: 202 '' 2012-10-12 03:21:28,356 DEBUG access object-store @ xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/provider-state 2012-10-12 03:21:28,357 DEBUG openstack: PUT 'xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/provider-state' 2012-10-12 03:21:28,446 DEBUG openstack: 201 '201 Created\n\n\n\n ' 2012-10-12 03:21:28,446 INFO 'bootstrap' command finished successfully Juju Status Command root@cinder01:/home/cinder# juju -v status 2012-10-12 03:23:28,314 DEBUG Initializing juju status runtime 2012-10-12 03:23:28,320 WARNING Verification of xxxxS certificates is disabled for this environment. Set 'ssl-hostname-verification' to ensure secure communication. 2012-10-12 03:23:28,320 DEBUG openstack: using auth-mode 'userpass' with xxxx:xxxxxx.10:35357/v2.0/ 2012-10-12 03:23:28,320 INFO Connecting to environment... 2012-10-12 03:23:28,403 DEBUG openstack: authenticated til u'2012-10-13T08:23:20Z' 2012-10-12 03:23:28,403 DEBUG access object-store @ xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/provider-state 2012-10-12 03:23:28,403 DEBUG openstack: GET 'xxxx:xx10.49.113.11:8080/v1/AUTH_d5f52673953f49e595279e89ddde979d/juju-hpc-az1-cb/provider-state' 2012-10-12 03:23:35,480 DEBUG openstack: 200 'zookeeper-instances: [a598b402-8678-4447-baeb-59255409a023]\n' 2012-10-12 03:23:35,480 DEBUG access compute @ xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023 2012-10-12 03:23:35,480 DEBUG openstack: GET 'xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023' 2012-10-12 03:23:35,662 DEBUG openstack: 200 '{"server": {"OS-EXT-STS:task_state": null, "addresses": {"private": [{"version": 4, "addr": "10.0.0.8"}, {"version": 4, "addr": "xxxx.37"}]}, "links": [{"href": "xxxx:xxxxxx.15:8774/v1.1/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023", "rel": "self"}, {"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/servers/a598b402-8678-4447-baeb-59255409a023", "rel": "bookmark"}], "image": {"id": "5bf60467-0136-4471-9818-e13ade75a0a1", "links": [{"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/images/5bf60467-0136-4471-9818-e13ade75a0a1", "rel": "bookmark"}]}, "OS-EXT-STS:vm_state": "active", "OS-EXT-SRV-ATTR:instance_name": "instance-00000060", "flavor": {"id": "1", "links": [{"href": "xxxx:xxxxxx.15:8774/d5f52673953f49e595279e89ddde979d/flavors/1", "rel": "bookmark"}]}, "id": "a598b402-8678-4447-baeb-59255409a023", "user_id": "01610f73d0fb4922aefff09f2627e50c", "OS-DCF:diskConfig": "MANUAL", "accessIPv4": "", "accessIPv6": "", "progress": 0, "OS-EXT-STS:power_state": 1, "config_drive": "", "status": "ACTIVE", "updated": "2012-10-12T08:21:40Z", "hostId": "1cdb25708fb8e464d83a69fe4a024dcd5a80baf24a82ec28f9d9f866", "OS-EXT-SRV-ATTR:host": "nova01", "key_name": "", "OS-EXT-SRV-ATTR:hypervisor_hostname": null, "name": "juju openstack instance 0", "created": "2012-10-12T08:21:22Z", "tenant_id": "d5f52673953f49e595279e89ddde979d", "metadata": {}}}' 2012-10-12 03:23:35,663 DEBUG Connecting to environment using xxxx.37... 2012-10-12 03:23:35,663 DEBUG Spawning SSH process with remote_user="ubuntu" remote_host="xxxx.37" remote_port="2181" local_port="45859". 2012-10-12 03:23:36,173:4355(0x7fd581973700):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.5 2012-10-12 03:23:36,173:4355(0x7fd581973700):ZOO_INFO@log_env@662: Client environment:host.name=cinder01 2012-10-12 03:23:36,174:4355(0x7fd581973700):ZOO_INFO@log_env@669: Client environment:os.name=Linux 2012-10-12 03:23:36,174:4355(0x7fd581973700):ZOO_INFO@log_env@670: Client environment:os.arch=3.2.0-23-generic 2012-10-12 03:23:36,174:4355(0x7fd581973700):ZOO_INFO@log_env@671: Client environment:os.version=#36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 2012-10-12 03:23:36,174:4355(0x7fd581973700):ZOO_INFO@log_env@679: Client environment:user.name=cinder 2012-10-12 03:23:36,174:4355(0x7fd581973700):ZOO_INFO@log_env@687: Client environment:user.home=/root 2012-10-12 03:23:36,175:4355(0x7fd581973700):ZOO_INFO@log_env@699: Client environment:user.dir=/home/cinder 2012-10-12 03:23:36,175:4355(0x7fd581973700):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=localhost:45859 sessionTimeout=10000 watcher=0x7fd57f9146b0 sessionId=0 sessionPasswd= context=0x2c1dab0 flags=0 2012-10-12 03:23:36,175:4355(0x7fd577fff700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:45859] zk retcode=-4, errno=111(Connection refused): server refused to accept the client 2012-10-12 03:23:39,512:4355(0x7fd577fff700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:45859] zk retcode=-4, errno=111(Connection refused): server refused to accept the client 2012-10-12 03:23:42,848:4355(0x7fd577fff700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:45859] zk retcode=-4, errno=111(Connection refused): server refused to accept the client ^Croot@cinder01:/home/cinder#

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• Which server software and configuration to retrieve from multiple POP servers, routing by address to correct user

  - by rolinger

  I am setting up a small email server on a Debian machine, which needs to pick up mail from a variety of POP servers and figure out who to send it to from the address, but I'm not clear what software will do what I need, although it seems like a very simple question! For example, I have 2 users, Alice and Bob. Any email to [email protected] ([email protected] etc) should go to Alice, all other mail to domain.example.com should go to Bob. Any email to [email protected] should go to Bob, and [email protected] should go to Alice Anything to *@bobs.place.com should go to Bob And so on... The idea is to pull together a load of mail addresses that have built up over the years and present them all as a single mailbox for Bob and another one for Alice. I'm expecting something like Postfix + Dovecot + Amavis + Spamassassin + Squirrelmail to fit the bill, but I'm not sure where the above comes in, can Postfix deal with it as a set of defined regular expressions, or is it a job for Amavis, or something else entirely? Do I need fetchmail in this mix, or is its role now included in one of the other components above. I think of it as content-filtering, but everything I read about content-filtering is focussed on detecting spam rather than routing email.

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• Loop through several servers, find specific dlls , get the dll version, internal filename and path?

  - by Graham

  I am a newby to Powershell, and using PS v2. I can see the massive potential it has, but I just can't get the following code to work fully. I am trying to end up with a csv file that contains the wild carded required dlls in the GAC_MSIL or sub-directory, get the dll version, internal filename and path, and the server IP address. The code is below, and it is in single line format because it appears easier to remote onto one of the servers in the server farm and run the single line from that console, ue to security log-ins etc. The code has produced a set of results, but only for the last server, it probably does the first server, then overwrites it but I am not sure about that. I have done a lot of reading about using arrays, and custom objects, and had a go at doing that, but my scripting skills in PS are not yet up to it. Code: $out = "Ouput_dll_ver_results.csv";foreach ($server in '11.222.33.123', '11.222.33.124') {$VersionInfo = (Get-ChildItem \$server\C$\windows\assembly\GAC_MSIL -recurse -Include abc*.dll,def*.dll,ghi*.dll,jkl*.dll | Where-Object { $.FullName -notmatch "\windows\assembly\temp\" })}; $VersionInfo | %{Get-Command $.FullName} | select -expand File* |Export-Csv $out Can you please advise if/how the above code can be corrected, and if not, what alternatives do I have to get the information I need. Many thanks in advance. Graham

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• AD domain on web servers behind NAT - DNS issues?

  - by Ant

  I'm trying to setup an AD domain to manage the security between two Windows Server 2008 webservers that will sooner or later use NLB to balance website requests. I've hit a problem which I think is a simple solution and is down to DNS. My website domain is mydomain.com. The two servers are running behind a NAT firewall on the 10.0.0.0 IP range. I've setup the AD domain to be called ad.mydomain.com (as recommended by MS and a few other answers to questions on here). The second web server however doesn't want to join the domain, and gives an error pinning the problem on DNS - "ensure that the domain name is typed correctly" even though it queries the SRV record successfully and gets the correct DC back - dc.ad.mydomain.com. Doing a dcdiag /test:dns on the DC gives the Delegation error 'DNS Server dc.mydomain.com Missing glue A record'. I have a feeling I need to add something to the public DNS so that it in some way knows about ad.mydomain.com. Can anyone suggest whether I'm on the right track in adding something to the public DNS? Or whether it's something else? Many thanks

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• Multiple LDAP servers with mod_authn_alias: failover not working when the first LDAP is down?

  - by quanta

  I've been trying to setup redundant LDAP servers with Apache 2.2.3. /etc/httpd/conf.d/authn_alias.conf <AuthnProviderAlias ldap master> AuthLDAPURL ldap://192.168.5.148:389/dc=domain,dc=vn?cn AuthLDAPBindDN cn=anonymous,ou=it,dc=domain,dc=vn AuthLDAPBindPassword pa$$w0rd </AuthnProviderAlias> <AuthnProviderAlias ldap slave> AuthLDAPURL ldap://192.168.5.199:389/dc=domain,dc=vn?cn AuthLDAPBindDN cn=anonymous,ou=it,dc=domain,dc=vn AuthLDAPBindPassword pa$$w0rd </AuthnProviderAlias> /etc/httpd/conf.d/authz_ldap.conf # # mod_authz_ldap can be used to implement access control and # authenticate users against an LDAP database. # LoadModule authz_ldap_module modules/mod_authz_ldap.so <IfModule mod_authz_ldap.c> <Location /> AuthBasicProvider master slave AuthzLDAPAuthoritative Off AuthType Basic AuthName "Authorization required" AuthzLDAPMemberKey member AuthUserFile /home/setup/svn/auth-conf AuthzLDAPSetGroupAuth user require valid-user AuthzLDAPLogLevel error </Location> </IfModule> If I understand correctly, mod_authz_ldap will try to search users in the second LDAP if the first server is down or OpenLDAP on it is not running. But in practice, it does not happen. Tested by stopping LDAP on the master, I get the "500 Internal Server Error" when accessing to the Subversion repository. The error_log shows: [11061] auth_ldap authenticate: user quanta authentication failed; URI / [LDAP: ldap_simple_bind_s() failed][Can't contact LDAP server] Did I misunderstand? AuthBasicProvider ldap1 ldap2 only means that if mod_authz_ldap can't find the user in ldap1, it will continue with ldap2. It doesn't include the failover feature (ldap1 must be running and working fine)?

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• Is it worth hiring a hacker to perform some penetration testing on my servers ?

  - by Brann

  I'm working in a small IT company with paranoid clients, so security has always been an important consideration to us ; In the past, we've already mandated two penetration testing from independent companies specialized in this area (Dionach and GSS). We've also ran some automated penetration tests using Nessus. Those two auditors were given a lot of insider information, and found almost nothing* ... While it feels comfortable to think our system is perfectly sure (and it was surely comfortable to show those reports to our clients when they performed their due diligence work), I've got a hard time believing that we've achieved a perfectly sure system, especially considering that we have no security specialist in our company (Security has always been a concern, and we're completely paranoid, which helps, but that's far as it goes!) If hackers can hack into companies that probably employ at least a few people whose sole task is to ensure their data stays private, surely they could hack into our small business, right ? Does someone have any experience in hiring an "ethical hacker"? How to find one? How much would it cost? *The only recommendation they made us was to upgrade our remote desktop protocols on two windows servers, which they were able to access because we gave them the correct non-standard port and whitelisted their IP

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• Copy one db diagram from one db to another on different servers? (Same db)

  - by sah302

  I used the copy database wizard to copy my database from our test server to our production server, the database copied everything fine except for the diagram. Okay no problem, first I make sure the target database on production has the support objects created to use database diagraming. Then I select to import data from the other database and chose the dbo.sysdiagrams.Go through with the rest of the import data wizard, but then I get the following error: Validating (Error) Messages Error 0xc0202049: Data Flow Task: Failure inserting into the read-only column "diagram_id". (SQL Server Import and Export Wizard) Error 0xc0202045: Data Flow Task: Column metadata validation failed. (SQL Server Import and Export Wizard) Error 0xc004706b: Data Flow Task: "component "Destination - sysdiagrams" (31)" failed validation and returned validation status "VS_ISBROKEN". (SQL Server Import and Export Wizard) Error 0xc004700c: Data Flow Task: One or more component failed validation. (SQL Server Import and Export Wizard) Error 0xc0024107: Data Flow Task: There were errors during task validation. (SQL Server Import and Export Wizard) So apparently it didn't like that. What's the problem? I am pretty beginner in SQL Server and only do stuff via the GUI usually so am not sure what to do at this point. The databases are the same, but on different servers. Thanks!

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• Provider claiming "all web servers in the cloud are automatically kept in sync" - should I be skeptical?

  - by RobMasters

  I'm no expert in cloud computing - I've spent a fair bit of time researching it and various providers but am yet to get any hands-on experience with it. From what I've read about AWS and auto-scaling EC2 instances though, it seems as though each instance should be completely decoupled from all other instances. i.e. If content is uploaded to the web server's local filesystem from a custom CMS backend then that content won't be available if subsequently requested from a different web server in the auto-scaling group. Is that right? I met with a representative of our existing hosting provider recently and he was claiming that it isn't a problem that our legacy CMS system is highly dependent on having a local filesystem. He said that all web servers, regardless of how many, would be kept as exact duplicates so I shouldn't notice any difference compared to our existing setup of a single dedicated server. This smells a little too much like bull fecal-matter to me...should I be skeptical about this? I'm a little worried because my (non-technical) boss who ultimately makes the decisions is all for signing up to this cloud solution because it won't require any extra work. I'm sure that they must at least be able to provide this, otherwise they wouldn't be attempting to sell it to us. But at what cost? It sounds as though each web server will always need to be checking the other web server(s) for new static content, which to me sounds like unwanted overhead that'll slow things down. I'd really appreciate it if somebody could clear this up to me. I'm all for switching to AWS and using S3+CloudFront for all static content, but that isn't looking very likely to happen at the moment.

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• Symantec Backup Exec Error on backup

  - by AliGibbs

  Recently we have moved some of servers from real servers- into virtual servers. Since then, we are getting errors like the following: Error category : Resource ErrorsError : e000fed1 - A failure occurred querying the Writer status. For additional information regarding this error refer to link V-79-57344-65233 This is happening on the virtual servers and also the real servers now. Looked on google and found some information- like running "vssadmin list writers" however none of these are showing an error.

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• Lessons from a SAN Failure

  - by Bill Graziano

  At 1:10AM Sunday morning the main SAN at one of my clients suffered a “partial” failure.  Partial means that the SAN was still online and functioning but the LUNs attached to our two main SQL Servers “failed”.  Failed means that SQL Server wouldn’t start and the MDF and LDF files mostly showed a zero file size.  But they were online and responding and most other LUNs were available.  I’m not sure how SANs know to fail at 1AM on a Saturday night but they seem to.  From a personal standpoint this worked out poorly: I was out with friends and after more than a few drinks.  From a work standpoint this was about the best time to fail you could imagine.  Everything was running well before Monday morning.  But it was a long, long Sunday.  I started tipsy, got tired and ended up hung over later in the day. Note to self: Try not to go out drinking right before the SAN fails. This caught us at an interesting time.  We’re in the process of migrating to an entirely new set of servers so some things were partially moved.  This made it difficult to follow our procedures as cleanly as we’d like.  The benefit was that we had much better documentation of everything on the server.  I would encourage everyone to really think through the process of implementing your DR plan and document as much as possible.  Following a checklist is much easier than trying to remember at night under pressure in a hurry after a few drinks. I had a series of estimates on how long things would take.  They were accurate for any single server failure.  They weren’t accurate for a SAN failure that took two servers down.  This wasn’t bad but we should have communicated better. Don’t forget how many things are outside the database.  Logins, linked servers, DTS packages (yikes!), jobs, service broker, DTC (especially DTC), database triggers and any objects in the master database are all things you need backed up.  We’d done a decent job on this and didn’t find significant problems here.  That said this still took a lot of time.  There were many annoyances as a result of this.  Small settings like a login’s default database had a big impact on whether an application could run.  This is probably the single biggest area of concern when looking to recreate a server.  I’d encourage everyone to go through every single node of SSMS and look for user created objects or settings outside the database. Script out your logins with the proper SID and already encrypted passwords and keep it updated.  This makes life so much easier.  I used an approach based on KB246133 that worked well.  I’ll get my scripts posted over the next few days. The disaster can cause your DR process to fail in unexpected ways.  We have a job that scripts out all logins and role memberships and writes it to a file.  This runs on the DR server and pulls from the production server.  Upon opening the file I found that the contents were a “server not found” error.  Fortunately we had other copies and didn’t need to try and restore the master database.  This now runs on the production server and pushes the script to the DR site.  Soon we’ll get it pushed to our version control software. One of the biggest challenges is keeping your DR resources up to date.  Any server change (new linked server, new SQL Server Agent job, etc.) means that your DR plan (and scripts) is out of date.  It helps to automate the generation of these resources if possible. Take time now to test your database restore process.  We test ours quarterly.  If you have a large database I’d also encourage you to invest in a compressed backup solution.  Restoring backups was the single larger consumer of time during our recovery. And yes, there’s a database mirroring solution planned in our new architecture. I didn’t have much involvement in things outside SQL Server but this caused many, many things to change in our environment.  Many applications today aren’t just executables or web sites.  They are a combination of those plus network infrastructure, reports, network ports, IP addresses, DTS and SSIS packages, batch systems and many other things.  These all needed a little bit of attention to make sure they were functioning properly. Profiler turned out to be a handy tool.  I started a trace for failed logins and kept that running.  That let me fix a number of problems before people were able to report them.  I also ran traces to capture exceptions.  This helped identify problems with linked servers. Overall the thing that gave me the most problem was linked servers.  In order for a linked server to function properly you need to be pointed to the right server, have the proper login information, have the network routes available and have MSDTC configured properly.  We have a lot of linked servers and this created many failure points.  Some of the older linked servers used IP addresses and not DNS names.  This meant we had to go in and touch all those linked servers when the servers moved.

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• What is the standard way to deploy memcached?

  - by Tom

  I have two IIS servers and two MySQL servers. On all servers I have some available memory (More than a GB). What is the standard way to deploy memcached? Should I add a new server especially for memcached, or should I use my existing servers? If so, which servers? Thanks in advance

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• How do I protect a low budget network from rogue DHCP servers?

  - by Kenned

  I am helping a friend manage a shared internet connection in an apartment buildling with 80 apartments - 8 stairways with 10 apartments in each. The network is laid out with the internet router at one end of the building, connected to a cheap non-managed 16 port switch in the first stairway where the first 10 apartments are also connected. One port is connected to another 16 port cheapo switch in the next stairway, where those 10 apartments are connected, and so forth. Sort of a daisy chain of switches, with 10 apartments as spokes on each "daisy". The building is a U-shape, approximately 50 x 50 meters, 20 meters high - so from the router to the farthest apartment it’s probably around 200 meters including up-and-down stairways. We have a fair bit of problems with people hooking up wifi-routers the wrong way, creating rogue DHCP servers which interrupt large groups of the users and we wish to solve this problem by making the network smarter (instead of doing a physical unplugging binary search). With my limited networking skills, I see two ways - DHCP-snooping or splitting the entire network into separate VLANS for each apartment. Separate VLANS gives each apartment their own private connection to the router, while DHCP snooping will still allow LAN gaming and file sharing. Will DHCP snooping work with this kind of network topology, or does that rely on the network being in a proper hub-and-spoke-configuration? I am not sure if there are different levels of DHCP snooping - say like expensive Cisco switches will do anything, but inexpensive ones like TP-Link, D-Link or Netgear will only do it in certain topologies? And will basic VLAN support be good enough for this topology? I guess even cheap managed switches can tag traffic from each port with it’s own VLAN tag, but when the next switch in the daisy chain receives the packet on it’s “downlink” port, wouldn’t it strip or replace the VLAN tag with it’s own trunk-tag (or whatever the name is for the backbone traffic). Money is tight, and I don’t think we can afford professional grade Cisco (I have been campaigning for this for years), so I’d love some advice on which solution has the best support on low-end network equipment and if there are some specific models that are recommended? For instance low-end HP switches or even budget brands like TP-Link, D-Link etc. If I have overlooked another way to solve this problem it is due to my lack of knowledge. :)

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• Inside the Concurrent Collections: ConcurrentDictionary

  - by Simon Cooper

  Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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• SQL Developer Data Modeler v3.3 Early Adopter: Link Model Objects Across Designs

  - by thatjeffsmith

  The third post in our “What’s New in SQL Developer Data Modeler v3.3” series, SQL Developer Data Modeler now allows you to link objects across models. If you need to catch up on the earlier posts, here are the first two: New and Improved Search Collaborative Design via Excel Today’s post is a very simple and straightforward discussion on how to share objects across models and designs. In previous releases you could easily copy and paste objects between models and designs. Simply select your object, right-click and select ‘Copy’ Once copied, paste it into your other designs and then make changes as required. Once you paste the object, it is no longer associated with the source it was copied from. You are free to make any changes you want in the new location without affecting the source material. And it works the other way as well – make any changes to the source material and the new object is also unaffected. However. What if you want to LINK a model object instead of COPYING it? In version 3.3, you can now do this. Simply drag and drop the object instead of copy and pasting it. Select the object, in this case a relational model table, and drag it to your other model. It’s as simple as it sounds, here’s a little animated GIF to show you what I’m talking about. Drag and drop between models/designs to LINK an object Notes The ‘linked’ object cannot be modified from the destination space Updating the source object will propagate the changes forward to wherever it’s been linked You can drag a linked object to another design, so dragging from A - B and then from B - C will work Linked objects are annotated in the model with a ‘Chain’ bitmap, see below This object has been linked from another design/model and cannot be modified. A very simple feature, but I like the flexibility here. Copy and paste = new independent object. Drag and drop = linked object.

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• GWT: Generate more complete crawl error report

  - by Mike

  I'm a developer in charge of managing Webmasters and related issues (including correcting crawl errors) for dozens (hundreds, maybe?) of active sites and as part of my duties I create a report of every discrepancy, including all pages generating a 404 and all pages that link to those pages. Currently within Webmaster Tools I'm able to download a csv file of all pages with a 404 response, but I'm then having to manually click on every single one of those links and copy the "linked from" field to paste into my spreadsheet. This is extremely tedious and seems unnecessary; I would expect the ability to download all that data at once. I'm ultimately looking for the end result of one csv file that has every url with a 404, but also has every url that links to each one of them. Am I overlooking this functionality somewhere or does anyone have a good solution? Edit 1 (2/11/2013): Example of what the csv output looks like now: URL,Response Code,News Error,Detected,Category http://www.abcdef.com/123.php,404,,11/12/13,Not found http://www.abcdef.com/456.php,404,,11/12/13,Not found Which is great, but let's say 123.php has 5 pages that link to it. Now I have to duplicate that row in my spreadsheet 4 more times, then go into Webmasters, get all the url's that link to the page, and add that data to my spreadsheet. The output I would prefer: URL,Response Code,Linked From,News Error,Detected,Category http://www.abcdef.com/123.php,404,http://www.ghijkl.com/naughtypage1.php,,11/12/13,Not found http://www.abcdef.com/123.php,404,http://www.ghijkl.com/naughtypage2.php,,11/12/13,Not found http://www.abcdef.com/123.php,404,http://www.ghijkl.com/naughtypage3.php,,11/12/13,Not found http://www.abcdef.com/456.php,404,http://www.ghijkl.com/naughtypage1.php,,11/12/13,Not found http://www.abcdef.com/456.php,404,http://www.ghijkl.com/naughtypage2.php,,11/12/13,Not found http://www.abcdef.com/456.php,404,http://www.ghijkl.com/naughtypage3.php,,11/12/13,Not found Note the (hypothetical) addition of a "Linked From" column, as well as the fact there are only 2 unique URL's now (like before) but all of the "Linked To" pages are shown in one report. Edit 2 (2/12/2013): To clarify, my question is less about detecting and correcting 404's, but more about generating a report of what Google has listed as errors. Oftentimes, these errors aren't even valid anymore but I still need documentation to show that Google detected a problem and that problem is now fixed. Many of the "linked from" url's I find are actually outdated, cached resources. For example, I'll frequently see that the linked-from url is the sitemap, which is actually an old sitemap cached by Google that points to an old page. Neither the sitemap or old page exist, but they still appear in my crawl error reports because they are cached resources.

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• Google Analytics - TOS section pertaining to privacy

  - by Eike Pierstorff

  The Google Analytics terms of service does do not allow to track "data that personally identifies an individual (such as a name, email address or billing information), or other data which can be reasonably linked to such information by Google". Does anybody have first-hand knowledge if this includes user ids which cannot be resolved by Google but can be linked to actual persons via an Analytics Users CRM system (e.g. a CRM linked to Analytics via API access) ? I used to think so, but if that where the case many ecommerce implementations would be illegal (since they store transactions id which can be linked to client's purchases). If anybody has insights about the intended meaning of the paragraph (preferably with a reliable source) it would be great if he/she could share :-)

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