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• How use DNS server to create simple HA (High availability) of my website?

  - by marc22

  Welcome, How can i use DNS server to create simple HA (High availability) of website ? For example if my web-server ( for better understanding i use internal IP in real it will be other hosting companies) 192.168.0.120 :80 (is offline) traffic go to 192.168.0.130 :80 You have right, i use bad word "hight avability" of course i was thinking about failover. Using few IP in A records is good for simple load-balancing. But not in case, if i want notice user about failure (for example display page, Oops something is wrong without our server, we working on it) against "can't establish connection". I was thinking about setting up something like this 2 DNS servers, one installed on www server Both have low TTL on my domain, set up 2 ns records first for DNS with my apache server second to other dns If user try connect he will get ip of www server using first dns, if that dns is offline (probably www server is also down) so it will try second NS record, what will point to another dns, that dns will point to "backup" page. That's what i would like to do. If You have other idea please share. Reverse proxy is not option, because IP of server can change, or i can use other country for backup.

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• Configure an Azure VM for Dynamic DNS for Cloud Services

  - by Adam

  I am trying to setup an azure VM with proper DNS to allow multiple cloud services to communicate across cloud service boundaries. As I understand it, I need to provide my own DNS server. I do not have any on-premise infrastructure, so I am trying to configure an Azure VM to act as my DNS. This SO question (http://stackoverflow.com/questions/21858926/azure-how-to-connect-one-cloud-service-with-other-in-one-virtual-network) is very similar to my setup. This article (http://msdn.microsoft.com/en-us/library/windowsazure/jj156088.aspx) describes my particular case: Name resolution between virtual machines and role instances located in the same virtual network, but different cloud services Here is what I have done: Created Azure Virtual Network and declared subnets for each of my cloud services. Created an Azure VM (Windows 2012 R2) with DNS enabled RDP to the VM and enabled the DNS role and installed features Added the appropriate NetworkConfiguration xml section to each of my cloud services .csfg files Re-deployed my cloud services I have verified that I setup the virtual network and networkconfiguration properly because my cloud service hosts are able to communicate with each other if I use the internal ips. However, name resolution doesn't appear to be working, and it doesn't appear that my cloud service roles can communicate with my DNS server. How do I configure my VM so that my different cloud services roles register themselves with my DNS server? EDIT: I think I am 1 step closer to getting this to work. The cloud services that I was using are in an old affinity group which is not supported by VMs, so I was unable to add my VM into my virtual network. I created a new VNET in a new affinity group with my VM added into it. However, I still don't know how to configure the azure VM's DNS server so that the cloud services register themselves for name resolution. Also, an added bonus guaranteed to get a +1 would be to explain if it is possible to register a DNS entry for the VIP for an internal endpoint of my cloud services so we can get load balancing. Thanks!

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• ESX Scheduler and NUMA issue

  - by babyg_wc

  On our 24 core bl685 (4sockets x 6core), we find that NUMA nodes 0 and 1 are pretty busy (unfortunately resulting in elevated cpu ready times on the VMS), whilst NUMA nodes 2 and 3 are almost unused. I thought this just maybe a ESX4 U1 issue, so I had a colleague with a 32 core (dl785) farm investigate, and it seems that his last 3 or 4 NUMA nodes are also not really being utilised. ESX seems to have a weakness when it comes to balancing lightly loaded NUMA boxes, Im going to enabled node interleaving in the BIOS and see if the scheduler balancers across all 24 cores, instead of just 12!... For those of you with large core counts, I would suggest you fire up you viclient, and check Physical CPU useage (or esxtop), I would be interested to hear what your results are. Please note, that its only the lightly loaded (eg less than 30% cpu load on the esx host) that seems to have the biggest issue with load imbalance. Thoughts/comments. PS ive logged a SR with vmware to assist, also the other "problem" could be that we have 128gb of ram in each host, and therefore the scheduler sees no good reason why it shouldnt try and cram all vms's into the first two NUMA nodes, as we only have around 50gb of ram worth of vms on each host...

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• 3 Servers, is this is a cluster?

  - by Andy Barlow

  Hello, At the moment I have one Ubuntu server, 9.10, running with a simple Samba share, a mail server, DNS server and DHCP server. Mostly its just there for file sharing and email server. I also have 2 other servers that are exactly the same hardware and spec as the first, which have an rsync set up to retrieve the shared folders and backs them up. However, if the first server goes down, all of our shares disappear along with our mail and the system must be rebuilt. Also I tend to find if people are downloading a large amount from the file server, no-one can access there emails - especially in the morning when everyone is signing in at once. Would it be more beneficial for me to have all 3 servers, all running the same services, doing the same thing with some sort of cluster with load balancing? I'm not really sure where to begin looking, or how to go about such a setup where 3 servers are all identical, but perhaps one acts as the main load balancer?? If someone can point me in the right direction, or if this simply sounds like one of those Enterprise Cloud's that is now a default setup in Ubuntu Server 9.10+, then I'll go down that route. Cheers in advance. Andy

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• Nginx multiple upstream servers on the same domain via diferent url

  - by Barry

  Hello. I am trying to rout trafic to different upstream servers (that serve different applications and not for load balancing). The incoming trafic has the same domain name but different URL. Here is an example of my configuration: http { upstream backend1 { server 127.0.0.1:8080 fail_timeout=0; server 127.0.0.1:8081 fail_timeout=0; } upstream backend2 { server 127.0.0.1:8090 fail_timeout=0; server 127.0.0.1:8091 fail_timeout=0; } server { listen 80; server_name my_server.com; root /home/my_server; location /serve_me { fastcgi_pass backend1; include fastcgi_params; } location / { fastcgi_pass backend2; include fastcgi_params; } } } It seems that whatever trafic comes in (including "my_server.com/serve_me") goes to backend2. How do I make queries that start with /serve_me to be directed to backend1? Thanks, Barry.

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• Troubleshooting loss of network connectivity in Windows 2003 - What else to check?

  - by Benny

  We are facing a weird problem in our data center. Our Backup server (running EMC Networker) loses network connection every alternate day around 3:00 AM (Backup schedule starts at midnight). After 2 hours of outage, the network connectivity recovers automatically and back to normal. What we observed: It is unlikely to be network issue, since it is directly connected to server farm switch (layer 2 connection without any intermediate hops). Further, the server is connected to two different switches for Load balancing using Broadcomm Teaming. a) If it were a switch related issue it is unlikely that both the network ports go down, since they are connected to different switch. b) A possibility Vlan wide issue is also ruled out since other devices in the same Vlan are fine. c) Switch interface status is always up. But there are lot of packet drops during the outage period - Can be attributed to high interface utilization of the backup server (near 100%) d) Connectivity is restored without any change on network. Next suspect is resource utilization on Windows server. Both CPU and Memory have rarely exceeded 80%, but NIC card utilization is alarmingly high (near 100%) Not really sure how to investigate this?

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• IIS 7.5 stops serving requests for no apparent reason

  - by Steffen

  We're running a site on 4 virtual Win 2008 R2 64 bit servers. This is the only site on the IIS, and we use Windows Network Load Balancing to share the load between our 4 virtual servers. We've used these virtual servers for approximately a week, and we're starting to see some issues. For no apparent reason the IIS stops serving pages, and doesn't even respond with an error. So upon requesting a page from the server, the browser just waits infinitely (or until it decides to give up clientside) Sometimes an iisreset fixes the issue, other times we have to reboot the entire virtual server. There are no traces in the eventlog of why this happens, and there's no traces in our applications exception log neither. Furthermore this happens even when there's a very small load on the server, so it doesn't seem to be because it's flooded with requests. So frankly I'm at a loss here - I have no idea where to start debugging this issue :-( I'm quite certain we never had these issues on our physical servers, however they were running Win 2003 32bit, so there are quite a few differences between them and the virtual ones. (Which obviously makes it difficult to tell what exactly causes this)

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• Pros and Cons of a proxy/gateway server

  - by Curtis

  I'm working with a web app that uses two machines, a BSD server and a Windows 2000 server. When someone goes to our website, they are connected to the BSD server which, using Apache's proxy module, relays the requests & responses between them and the web server on the Windows server. The idea (designed and deployed about 9 years ago) was that it was more secure to have the BSD server as what outside people connected to than the Windows server running the web app. The BSD server is a bare bones install with all unnecessary services & applications removed. These servers are about to be replaced and the big question is, is a cut-down, barebones server necessary for security in this setup. From my research online I don’t see anyone else running a setup like this (I don't see anyone questioning it at least.) If they have a server between the user and the web app server(s), it is caching, compressing, and/or load balancing. Is there anything I’m overlooking by letting people connect directly from the internet ** to a Windows 2008 R2 server that’s running the web application? ** there’s a good hardware firewall between the internet with only minimal ports open Thank you.

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• Which is more secure: Tomcat standalone or Tomcat behind Apache?

  - by NoozNooz42

  This question is not about performance, nor about load-balancing, etc. Which would be more secure: running Tomcat in standalone mode or running Tomcat behind apache? The thing is, Tomcat is written in Java and hence it is pretty much immune to buffer overrun/overflow (unless a buffer overrun in a C-written lib used by Tomcat can be triggered, but they're rare [the last I remember was in zlib, many many moons ago] and one heck of a hack to actually exploit), which gets rid of a lot of potential exploits. This page: http://wiki.apache.org/tomcat/FAQ/Security has this to say: There have been no public cases of damage done to a company, organization, or individual due to a Tomcat security issue... there have been only theoretical vulnerabilities found. All of those were addressed even though there were no documented cases of actual exploitation of these vulnerabilities. This, combined with the fact that buffer overrun/overflow are pretty much non-existent in Java, makes me believe that Tomcat in standalone mode is pretty secure. In addition to that, I can install both Java and Tomcat on Linux without needing to be root. The only moment I need to be root is to set up a transparent port 8080 to port 80 forwarding (and 8443 to 443). Two iptables line as root, that's all root is needed for. (I don't know for Apache). Apache is much more used than Tomcat and definitely does not have a security track record as good as Tomcat. What would make Tomcat + Apache more secure? What would make Tomcat + Apache less secure? In short: which is more secure, Tomcat standalone or Tomcat with Apache? (remembering that performance aren't an issue here)

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• Nginx, HAproxy, Unicorn, Rails and Node settings

  - by Julien Genestoux

  Our application is currently only a "regular" web app, with no fancy things like streaming HTTP or websockets. It's mostly a Rails app, served by a few (20 on 2 machines) Unicorn workers, proxied by a venerable nginx server which deals with load balancing. This has been working quite well for the past year and the app now serves between 400 and 800 requests per second at any point during the day. We're soon releasing 2 new APIs, which are both served by a Node application : a websocket one, as well as a long polling HTTP one. (the fancy thing like the Twitter streaming API where HTTP connections never end). They both use the same port on node and since the node app is stateless, we can certainly deploy a few of them to handle the traffic. The app (node) is now deployed in 5 instances and are now listening on 5 different 'private' ports on the same host. We need to put something in front of them to load balance, but also something that is able to deal with sockets (either websocket or HTTP streaming) which are intended to stay 'up' for days. The question is then : what? I read somewhere that HAProxy does a better job than Nginx at this. What do you recommend?

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• Can a pool of memcache daemons be used to share sessions more efficiently?

  - by Tom

  We are moving from a 1 webserver setup to a two webserver setup and I need to start sharing PHP sessions between the two load balanced machines. We already have memcached installed (and started) and so I was pleasantly surprized that I could accomplish sharing sessions between the new servers by changing only 3 lines in the php.ini file (the session.save_handler and session.save_path): I replaced: session.save_handler = files with: session.save_handler = memcache Then on the master webserver I set the session.save_path to point to localhost: session.save_path="tcp://localhost:11211" and on the slave webserver I set the session.save_path to point to the master: session.save_path="tcp://192.168.0.1:11211" Job done, I tested it and it works. But... Obviously using memcache means the sessions are in RAM and will be lost if a machine is rebooted or the memcache daemon crashes - I'm a little concerned by this but I am a bit more worried about the network traffic between the two webservers (especially as we scale up) because whenever someone is load balanced to the slave webserver their sessions will be fetched across the network from the master webserver. I was wondering if I could define two save_paths so the machines look in their own session storage before using the network. For example: Master: session.save_path="tcp://localhost:11211, tcp://192.168.0.2:11211" Slave: session.save_path="tcp://localhost:11211, tcp://192.168.0.1:11211" Would this successfully share sessions across the servers AND help performance? i.e save network traffic 50% of the time. Or is this technique only for failovers (e.g. when one memcache daemon is unreachable)? Note: I'm not really asking specifically about memcache replication - more about whether the PHP memcache client can peak inside each memcache daemon in a pool, return a session if it finds one and only create a new session if it doesn't find one in all the stores. As I'm writing this I'm thinking I'm asking a bit much from PHP, lol... Assume: no sticky-sessions, round-robin load balancing, LAMP servers.

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• qsub: How can I find out what DRM middleware exactly is installed on a cluster?

  - by gojira

  I have a user account on a very big cluster. I have previous experience with Grid Engine and want to use the cluster for array jobs. The documentation tells me to use "qsub" for load balancing / submission of many jobs. Therefore I assumed this means the cluster has Grid Engine. However all my Grid Engine scripts failed to run. I checked the documentation and it is a bit weird. Now I slowly suspect that this cluster does not actually have Grid Engine, maybe it's running something called Torque (?!). The whole terminology in the man pages is a bit weird for me as a Grid Engine user, for example they talk about "bulk jobs" instead of "array jobs". There is no referral to variables on which I rely on, like SGE_TASK_ID etc. Instead they refer to variables starting with PBS_. Still, there are qsub and qstat commands. Also qsub behaves differently, apparently it is not possible to specifiy the command line parameters with bash-script comments etc. There is a documentation for the cluster system, but it does not say what the DRM middleware actually is - it refers to the entire DRM system simply as "qsub". I tried qsub --version qsub: 1.2 2010/8/17 I am not sure what I am actually running when I invoke qsub on that cluster! My question is, how can I find out if I am running Grid Engine or Torque (or whatever it is), and which version?

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• Walkthrough/guide building aplication server for multi tenant web app [on hold]

  - by Khalid Adisendjaja

  The web app will detect a subdomain such as tenant1.app.com, tenant2.app.com, etc to identify tenant environment, each tenant environment will have a different database credential (port,db name,etc) but still connecting to the same database server. Each tenant should use app.com for their main domain, using their own domain is prohibitted. Each tenant will have their own rest api endpoint such as tenant1.app.com/api/v1/xxxx, tenant2.app.com/api/v1/xxxx, tenant3.app.com/api/v1/xxxx I've come to a simple solution by setting a wildcard subdomain (*.app.com) on webserver Apache/Nginx vhost configuration file. I have googled so many concept for building a multi-tenant app server but still don't understand how to really done it, what is the right way to do it and what is actually required to do this task. So I've come to this questions, Do I need a proxy server, dns masking, etc.. How to monitor each tenants activity What about server performance, load balancing, and scalability How to setup ssl certificate for each tenant what about application cache for each tenant Is it reliable to use the setup for production etc ... I have a very litte experience on server infrastructure, so I'm looking for a DIY walkthrough, step by step guide, or sophisticate solution ready to implemented for production

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• How do I load balance between two Linux machines?

  - by William Hilsum

  Inspired by the Stack Overflow network, I am now obsessed with HAProxy and trying to use it myself. At the moment, each HAProxy box has got two network cards (well, two configured, I can have a maximum of 4 and wasn't sure if they needed their own one for management between the boxes). On both machines, the backend one (eth1) is a private IP that goes to a switch connected to the webservers, and the front facing one (eth0) has a public internet IP that is routed straight though. In addition, I have created an additional virtual ip for eth0 called eth0:0 which has got a third public ip address. I just about get how to use it for load balancing between multiple web servers that are behind it, but, I am failing to load balance between the two HAProxy boxes - they appear to fight for the virtual IP, but, this does not appear to be a smart solution. Now, by using the virtual shared IP address, this solution appears to work and does seem to give me maximum uptime, but, is this the correct way to do it, or is there a smarter way? I have been looking at other Linux packages such as keepalived, but, I have only been using Linux (server) for a week now and am at the limits of my understanding. Is there anyone who has done this before and can you advise anything for maximum uptime?

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• What's the piece of hardware listening on Facebook's or Wikipedia's IP address?

  - by Igor Ostrovsky

  I am trying to understand how massive sites like Facebook or Wikipedia work, for my intellectual curiosity. I read about various techniques for building scalable sites, but I am still puzzled about one particular detail. The part that confuses me is that ultimately, the DNS will map the entire domain to a single IP address, or a handful of IP addresses in the case of round-robin DNS. For example, wikipedia.org has only one type-A DNS record. So, people from all over the world visiting Wikipedia have to send a request to the one IP address specified in DNS. What is the piece of hardware that listens on the IP address for a massive site, and how can it possibly handle all the load coming from the requests for users all over the world? Edit 1: Thanks for all the responses! Anycast seems like a feasible answer... Does anyone know of a way to check whether a particular IP address is anycast-routed, so that I could verify that this really is the trick used in practice by large sites? Edit 2: After more reading on the topic, it appears that anycast is not typically used for dynamic web content. Anycast is usually used for UDP (e.g., DNS lookups), or sometimes for static content. One interesting thing to note is that Facebook uses profile.ak.fbcdn.net to host static content like style sheets and javascript libraries. Each time I ping this name, I get a response from a different IP address. However, I can't tell whether this is anycast in action, or a completely different technique. Back to my original question: as far as I can tell, even a large site will have a single expensive piece of load-balancing hardware listening on its handful of public IP addresses.

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• IIS WebServer CreatesNew file: OwnerShip?

  - by Beaud.

  IIS is configured for Integrated Windows Authentication. web.config is configured as follows: <authentication mode="Windows" /> <identity impersonate="true" /> We are Load balancing between \webserver1 and \webserver2. Windows Server 2003 \\webserverX creates a XML file to \\share1 and access is denied. We got pass through access denial by allowing Everyon to access the share... We would like to have the impersonated user to be the owner of the created file. Instead, \\webserver1's computer account is the owner. How can we make sure that the impersonated user has ownership of the file at creation time? PROGRESSION: I decided to create the file locally on \\webserver1's root directory. File's ownership is NETWORK SERVICES even if impersonate="true". I'm unable to change ownership of the file in C# code. Why when creating a file, IIS won't use the impersonated user's write permissions? If it actually does, what I am doing wrong?

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• Bash Parallelization of CPU-intensive processes

  - by ehsanul

  tee forwards its stdin to every single file specified, while pee does the same, but for pipes. These programs send every single line of their stdin to each and every file/pipe specified. However, I was looking for a way to "load balance" the stdin to different pipes, so one line is sent to the first pipe, another line to the second, etc. It would also be nice if the stdout of the pipes are collected into one stream as well. The use case is simple parallelization of CPU intensive processes that work on a line-by-line basis. I was doing a sed on a 14GB file, and it could have run much faster if I could use multiple sed processes. The command was like this: pv infile | sed 's/something//' > outfile To parallelize, the best would be if GNU parallel would support this functionality like so (made up the --demux-stdin option): pv infile | parallel -u -j4 --demux-stdin "sed 's/something//'" > outfile However, there's no option like this and parallel always uses its stdin as arguments for the command it invokes, like xargs. So I tried this, but it's hopelessly slow, and it's clear why: pv infile | parallel -u -j4 "echo {} | sed 's/something//'" > outfile I just wanted to know if there's any other way to do this (short of coding it up myself). If there was a "load-balancing" tee (let's call it lee), I could do this: pv infile | lee >(sed 's/something//' >> outfile) >(sed 's/something//' >> outfile) >(sed 's/something//' >> outfile) >(sed 's/something//' >> outfile) Not pretty, so I'd definitely prefer something like the made up parallel version, but this would work too.

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• White Screen, No Errors.

  - by GruffTech

  So.. Interesting problem for you guys, As I'm completely lost as to what to do, or where to take the next step. Server & Application Environment. CentOS release 5.3 (Final) Apache 2.2.3-22 EnableSendfile off EnableMMAP off ErrorLog logs/error_log LogLevel debug PHP-5.2.6-2 error_reporting = E_ALL display_errors = on log_errors = on max_execution_time=300 max_input_time=60 memory_limit=512mb Kohana 2.3 PHP Environment. HAProxy 1.3.15.6-2 MemCacheD 1.2.6-1 Our application is split between 3 web servers, mounting a NFS Storage server, and sticky load balancing between the 3 web servers. The application seemingly runs great, but every so often, instead of loading, the application just shows a pure white page. Not a 404 Error, or a 500 Server Error, a clean white page. And it returns instantly, so its not a execution time error. Nothing in the Error log, or Server-Error Log, Proxy log shows standard proxied connection, Just the standard 200-Status in Access log, with 256 bytes transferred. To me, this leads to tell me that the application itself is having a problem. A rare, unexplainable, seemingly random, problem that causes what we've now called the "White Screen of Death." Our developers all say that since there is nothing going to our error logs, that it must be a server problem. But I say the same thing, There's nothing going to ANY of our logs (relevent to this anyway), and we're not having httpd children crash from what i can tell. Any ideas on how i can increase my logs, or somehow prove that its not a bug in PHP, Apache, CentOS, ect? Or if it is somehow a bug, identify it?

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• Running HTTP and HTTPS connections for a single domain (say, www.example.com) through a Cisco ACE SS

  - by Paddu

  My web application config has a Cisco ACE load balancing across a server farm and I want to use the ACE as an SSL endpoint as well. To make this work, the network architect has come up with a design where all secure pages have to be served from secure.my-domain.com, while non-secure pages are served up from www.my-domain.com. The reason for this is apparently that the configuring the Cisco ACE to accept HTTPS requests on port 443 for a particular public IP prevents the simultaneous acceptance of HTTP requests on port 80 for the same IP. While I'm not a networking (or Cisco) expert, this seems to be intuitively wrong, as it would prevent any website using the Cisco ACE to serve pages on http://www.my-domain.com and https://www.my-domain.com simultaneously. In this situation, my questions are: Is this truly a limitation of the Cisco ACE when used as an SSL endpoint? If not, then can I assume that we can set up the ACE to accept connections for a particular IP on ports 80 and 443, and function as an SSL endpoint for the incoming requests on 443? Links to appropriate documentation most welcome here. Assuming the setup in the previous question, can I then redirect both sets of requests to the same server farm on the same port?

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• Server 2003 PDC DNS not working..Failover server is...

  - by Seth

  In the midst of trying to utilize proc power, i create a fault tolerant DNS server a while ago. Since, Ive been trying to add another controller for exchange. So I thought I would revert back to a single primary DNS for the meantime and now Im balancing on a thread. The server i thought I uninstalled DNS, is still acting as DNS. And now the PDC does not resolve. Can anybody walk me through, Im overwhelmed and cant think straight... Im afraid if anyone restarts their machine they wont have internet. Update Ok so from the beginning. I was configuring Exchange on a new server 2008. How it happened I dont know, but it started to not resolve DNS. (exclamation mark on NIC) even though everything was static. So ultimately I decided to remove the server from the problem, because I noticed DNS was in disarray if I used the DNS IP of the first server. This is when I tested with nslookup on each DNS server. I had uninstalled DNS from the second server, but nslookup was still resolving with that IPaddress, which has me all wound up cause I dont understand. So, since the first DNS server isn't resolving, Im assuming if the second one isnt configured right I'll loose internet. Im just confused and dont know where to start troubleshooting...

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• Is Cherokee (probably) the best static content server for beginner sysadmins?

  - by Bad Learner

  I have read the pros and cons of most of the popular web servers and have come to a conclusion that Apache would (probably) be the best web server for serving dynamic content - - no wonder YouTube, Flickr and Facbook, among many others, use it. I do not know if that C10K problem applies to Apache even when serving dynamic content only, but I think any web server used to serve dynamic content needs some good tweaking for optimized performance, and the fact that nothing beats Apache when it comes to documentation, resources and support on the web, I think should will go with Apache for dynamic content. That apart, the confusion begins when it comes to choosing web servers for static content (including streaming videos). I see that Nginx, Cherokee and Lighttpd are among the best (I am not considering non-open source or non-linux stuff here). So, which too choose? I know one cannot go wrong with any of the three (Nginx, Cherokee, Lighttpd). Lighttpd's development has evidently gotten slower than it was a good time ago. The documentation is pretty good for all the three, and hopefully, so are the resources (knowledge of these among the users of Stackoverflow/Serverfault sites, the web etc). Precisely, and noting point [2] and [3], if I am not wrong, I should either go with Nginx or Cherokee. I would love to see someone clarify these... is Cherokee just as fast (mb/s), performant (connections/s), and reliable (think downtime/restarting server) as Nginx for serving static content and load balancing, for small, medium to large (and really large) websites and applications? (Think, the size of YouTube, Apache or Facebook.) if the answer for the Q above is a big "hell, yes!" then, I should probably prefer Cherokee, right? Because, since I am a beginner, it would a lot easier to setup Cherokee as it has a graphical admin user interface + really good documentation. Yes? I could be wrong, I could be right. I put down what I know so that you can offer most relevant advise. Pardon if anything I've said is offensive.

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• Monitoring AWS Systems Behind ElasticBeanStalk

  - by A. Avadis

  So I'm getting a company set up in the Amazon Cloud -- creating IAAS protocol/solutions/standardized implementation, etc while also being the SysAdmin for individual systems, app environments, and day-to-day uptime. One of the biggest issues I'm having is tracking various system/application logs, as well as logging/monitoring/archiving system metrics like memory usage, cpu usage, etc etc In a centralized fashion. E.g. -- Nagios + Urchin. The BIGGEST impediment to my endeavors is the following: The company application is deployed in the form of a Java *.WAR file, uploaded to an Elastic BeanStalk application environment, load balancing and auto-scaling between 3(min) and 10(max) servers, and the EC2's that run the application are fired up and disposed of ad-hoc. That is to say, I can't monitor the individual EC2's for very long because so many are being terminated then auto-provisioned/auto-scaled on the fly -- so I'd constantly be having to "monitor what I'm monitoring", and continuously remove/add EC2 machine addresses to my monitoring lists. IS there some sort of way to use monitoring tools like Zabbix or Nagios to monitor the ElasticBeanStalk, and have it automatically add on new EC2's, and remove terminated/failed EC2's from its monitoring list automatically? Furthermore, is there anything I can do with GrayLog to achieve similar results with the aggregation/centralization of my application logs from multiple EC2 instances into ONE consolidated set of logs/events? If not GrayLog, is there ANYTHING LIKE GrayLog that can automatically detect what EC2 members are being added/removed from the environment, and collect the logs from them automatically? Any and all advice or direction is appreciated. Thanks much, and cheers!!

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• Squid reverse proxy array - siblings not communicating with each other

  - by V. Romanov

  I want to set up 2 squid servers to act as reverse proxy and cache for a webserver on our intranet. The load balancing will be done with DNS round robin or just different mappings for different clients. The thing is, I want both servers to try and contact each other to see if they have the object required in cache before contacting the webserver for it (the network that servers the webserver is the bottleneck and I'm trying to eliminate it) Both squids are configured the same, here are the relevant config lines : acl dvr1_cache_it_best_tv_com dstdomain dvr1.cache.it.best-tv.com acl squid1_it_best_tv_com dstdomain squid1.it.best-tv.com acl squid2_it_best_tv_com dstdomain squid2.it.best-tv.com http_access allow dvr1_cache_it_best_tv_com http_access allow squid1_it_best_tv_com http_access allow squid2_it_best_tv_com http_access allow all http_port 8081 accel defaultsite=dvr1.cache.it.best-tv.com cache_peer dvr1.origin.it.best-tv.com parent 80 0 no-query originserver name=Proxy_dvr1_origin_it_best_tv_com cache_peer squid1.it.best-tv.com sibling 8081 3130 weight=10 name=Proxy_Squid1_it_best_tv_com cache_peer squid2.it.best-tv.com sibling 8081 3130 weight=10 name=Proxy_Squid2_it_best_tv_com cache_peer_access Proxy_dvr1_origin_it_best_tv_com allow dvr1_cache_it_best_tv_com cache_peer_access Proxy_squid1_it_best_tv_com allow squid1_it_best_tv_com cache_peer_access Proxy_squid1_it_best_tv_com allow squid2_it_best_tv_com cache_peer_access Proxy_squid1_it_best_tv_com allow dvr1_cache_it_best_tv_com cache_peer_access Proxy_squid2_it_best_tv_com allow squid1_it_best_tv_com cache_peer_access Proxy_squid2_it_best_tv_com allow squid2_it_best_tv_com cache_peer_access Proxy_squid2_it_best_tv_com allow dvr1_cache_it_best_tv_com just to make it clear - dvr1.cache is the alias for the proxy servers. dvr1.origin is the web server. Both servers work, both serve content and cache it and work fine. However, when I clear the cache on one server and then access it, it gets the content from the parent (DVR1_ORIGIN) instead of going to the sibling squid. What did I configure wrong? Or perhaps I don't understand the architecture correctly? I read the squid manuals but as far as I see i did it all by the book and yet it doesn't work right. Any help will be appreciated!

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• How browsers handle multiple IPs

  - by Sandman4

  Can someone direct me to information on exact browsers behavior when browser gets multiple A records for a given hostname (say ip1 and ip2), and one of them is not accessible. I interested in EXACT details, like (but not limited to): Will browser get 2 IPs from OS, or it will get only one ? Which ip will browser try first (random or always the first one) ? Now, let's say browser started with the failed ip1 For how long will browser try ip1 ? If user hits "stop" while it waits for ip1, and then clicks refresh which IP will browser try ? What will happen when it times-out - will it start trying ip2 or give error ? (And if error, which ip will browser try when user clicks refresh). When user clicks refresh, will any browser attempt new DNS lookup ? Now let's assume browser tried working ip2 first. For the next page request, will browser still use ip2, or it may randomly switch ips ? For how long browsers keep IPs in their cache ? When browsers sends a new DNS request, and get SAME ips, will it CONTINUE to use the same known-to-be-working IP, or the process starts from scratch and it may try any of the two ? Of course it all may be browser dependent, and may also vary between versions and platforms, I'd be happy to have maximum of details. The purpose of this - I'm trying to understand what exactly users will experience when round-robin DNS based used and one of the hosts fails. Please, I'm NOT asking about how bad DNS load balancing is, and please refrain from answering "don't do it", "it's a bad idea", "you need heartbeat/proxy/BGP/whatever" and so on.

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• Good Enough Failover Strategy for DNS / MySQL / Email

  - by IMB

  I've asked and read a lot questions regarding DNS failover but the more I read the more complicated it becomes, some people say it's good enough some say it isn't. No clear answers from what I read. I was wondering if we can set it straight once and for all, at least for the requirements of most websites out there. Right now let's assume the following: We don't need really need load-balancing, what we need is a failover solution. We are running a website based on LAMP on a VPS. We need to make sure that the Web Server, MySQL, Email are always accessible if not 99%. Basically here's my idea and questions about it: Web Server: We need at least one failover server (another VPS on a separate data center). Is DNS Failover via Round Robin good, if not, what's the best? And how do you exactly implement it? How do you make the files you upload/delete on Server A is also on Server B? MySQL: I've only read a brief intro to MySQL replication and I assume that I can replicate Server A to Server B and vice versa on the fly right? So just it case Server A fails and Server B is now running, it will continue to work and replicate to Server A when it becomes available. So in essence Server B is now the primary server, and will later on failover to Server A, should a failure happen again. Email: If we are gonna use DNS Failover, using webmail or relying on emails stored on the server is probably not a good idea right? Since some emails might be on Server A while some might be on Server B? I assume a basic email forwarder to a 3rdparty is good enough (like Gmail for example) to ensure all emails are kept in one place. Here's a basic diagram for a better picture: http://i.stack.imgur.com/KWSIi.png

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