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• The Growing Importance of Network Virtualization

  - by user12608550

  The Growing Importance of Network Virtualization We often focus on server virtualization when we discuss cloud computing, but just as often we neglect to consider some of the critical implications of that technology. The ability to create virtual environments (or VEs [1]) means that we can create, destroy, activate and deactivate, and more importantly, MOVE them around within the cloud infrastructure. This elasticity and mobility has profound implications for how network services are defined, managed, and used to provide cloud services. It's not just servers that benefit from virtualization, it's the network as well. Network virtualization is becoming a hot topic, and not just for discussion but for companies like Oracle and others who have recently acquired net virtualization companies [2,3]. But even before this topic became so prominent, Solaris engineers were working on technologies in Solaris 11 to virtualize network services, known as Project Crossbow [4]. And why is network virtualization so important? Because old assumptions about network devices, topology, and management must be re-examined in light of the self-service, elasticity, and resource sharing requirements of cloud computing infrastructures. Static, hierarchical network designs, and inter-system traffic flows, need to be reconsidered and quite likely re-architected to take advantage of new features like virtual NICs and switches, bandwidth control, load balancing, and traffic isolation. For example, traditional multi-tier Web services (Web server, App server, DB server) that share net traffic over Ethernet wires can now be virtualized and hosted on shared-resource systems that communicate within a larger server at system bus speeds, increasing performance and reducing wired network traffic. And virtualized traffic flows can be monitored and adjusted as needed to optimize network performance for dynamically changing cloud workloads. Additionally, as VEs come and go and move around in the cloud, static network configuration methods cannot easily accommodate the routing and addressing flexibility that VE mobility implies; virtualizing the network itself is a requirement. Oracle Solaris 11 [5] includes key network virtualization technologies needed to implement cloud computing infrastructures. It includes features for the creation and management of virtual NICs and switches, and for the allocation and control of the traffic flows among VEs [6]. Additionally it allows for both sharing and dedication of hardware components to network tasks, such as allocating specific CPUs and vNICs to VEs, and even protocol-specific management of traffic. So, have a look at your current network topology and management practices in view of evolving cloud computing technologies. And don't simply duplicate the physical architecture of servers and connections in a virtualized environment…rethink the traffic flows among VEs and how they can be optimized using Oracle Solaris 11 and other Oracle products and services. [1] I use the term "virtual environment" or VE here instead of the more commonly used "virtual machine" or VM, because not all virtualized operating system environments are full OS kernels under the control of a hypervisor…in other words, not all VEs are VMs. In particular, VEs include Oracle Solaris zones, as well as SPARC VMs (previously called LDoms), and x86-based Solaris and Linux VMs running under hypervisors such as OEL, Xen, KVM, or VMware. [2] Oracle follows VMware into network virtualization space with Xsigo purchase; http://www.mercurynews.com/business/ci_21191001/oracle-follows-vmware-into-network-virtualization-space-xsigo [3] Oracle Buys Xsigo; http://www.oracle.com/us/corporate/press/1721421 [4] Oracle Solaris 11 Networking Virtualization Technology, http://www.oracle.com/technetwork/server-storage/solaris11/technologies/networkvirtualization-312278.html [5] Oracle Solaris 11; http://www.oracle.com/us/products/servers-storage/solaris/solaris11/overview/index.html [6] For example, the Solaris 11 'dladm' command can be used to limit the bandwidth of a virtual NIC, as follows: dladm create-vnic -l net0 -p maxbw=100M vnic0

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• Using WKA in Large Coherence Clusters (Disabling Multicast)

  - by jpurdy

  Disabling hardware multicast (by configuring well-known addresses aka WKA) will place significant stress on the network. For messages that must be sent to multiple servers, rather than having a server send a single packet to the switch and having the switch broadcast that packet to the rest of the cluster, the server must send a packet to each of the other servers. While hardware varies significantly, consider that a server with a single gigabit connection can send at most ~70,000 packets per second. To continue with some concrete numbers, in a cluster with 500 members, that means that each server can send at most 140 cluster-wide messages per second. And if there are 10 cluster members on each physical machine, that number shrinks to 14 cluster-wide messages per second (or with only mild hyperbole, roughly zero). It is also important to keep in mind that network I/O is not only expensive in terms of the network itself, but also the consumption of CPU required to send (or receive) a message (due to things like copying the packet bytes, processing a interrupt, etc). Fortunately, Coherence is designed to rely primarily on point-to-point messages, but there are some features that are inherently one-to-many: Announcing the arrival or departure of a member Updating partition assignment maps across the cluster Creating or destroying a NamedCache Invalidating a cache entry from a large number of client-side near caches Distributing a filter-based request across the full set of cache servers (e.g. queries, aggregators and entry processors) Invoking clear() on a NamedCache The first few of these are operations that are primarily routed through a single senior member, and also occur infrequently, so they usually are not a primary consideration. There are cases, however, where the load from introducing new members can be substantial (to the point of destabilizing the cluster). Consider the case where cluster in the first paragraph grows from 500 members to 1000 members (holding the number of physical machines constant). During this period, there will be 500 new member introductions, each of which may consist of several cluster-wide operations (for the cluster membership itself as well as the partitioned cache services, replicated cache services, invocation services, management services, etc). Note that all of these introductions will route through that one senior member, which is sharing its network bandwidth with several other members (which will be communicating to a lesser degree with other members throughout this process). While each service may have a distinct senior member, there's a good chance during initial startup that a single member will be the senior for all services (if those services start on the senior before the second member joins the cluster). It's obvious that this could cause CPU and/or network starvation. In the current release of Coherence (3.7.1.3 as of this writing), the pure unicast code path also has less sophisticated flow-control for cluster-wide messages (compared to the multicast-enabled code path), which may also result in significant heap consumption on the senior member's JVM (from the message backlog). This is almost never a problem in practice, but with sufficient CPU or network starvation, it could become critical. For the non-operational concerns (near caches, queries, etc), the application itself will determine how much load is placed on the cluster. Applications intended for deployment in a pure unicast environment should be careful to avoid excessive dependence on these features. Even in an environment with multicast support, these operations may scale poorly since even with a constant request rate, the underlying workload will increase at roughly the same rate as the underlying resources are added. Unless there is an infrastructural requirement to the contrary, multicast should be enabled. If it can't be enabled, care should be taken to ensure the added overhead doesn't lead to performance or stability issues. This is particularly crucial in large clusters.

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• Printer Redirection from 2003 Terminal Server to 2008 Terminal Server

  - by xmaveric

  Our environment is a terminal server cluster (Win2003 servers) that everyone connects to do do their work. I have set up a new Win2008 R2 machine with the intention of using it to publish our main application to the TS farm. The idea was to keep this server dedicated to one application to avoid driver/dll conflicts with other software. I created a RemoteApp on the new server and made an .rdp file and placed it on the desktop of our TS farm servers. The problem I am running into is that when I connect to the RemoteApp, it doesn't show the printers that are installed on the TS server I am connecting from. We have over 20 printers installed on our TS servers, each with different drivers and permissions. I really do not want to reinstall all of these on the RemoteApp server so I was hoping Printer Redirection would handle this. It would appear that because the RDP client for Server 2003 x64 is 6.0, that version doesn't support the Easy Print feature (requires 6.1). I can't find any newer version on the MS site to download for Win2003 x64. How can I get the printers on the TS farm machine to redirect so they are viewed by the RemoteApp machine?

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• Web-based clients vs thick/rich clients?

  - by rudolfv

  My company is a software solutions provider to a major telecommunications company. The environment is currently IBM WebSphere-based with front-end IBM Portal servers talking to a cluster of back-end WebSphere Application Servers providing EJB services. Some of the portlets use our own home-grown MVC-pattern and some are written in JSF. Recently we did a proof-of-concept rich/thick-client application that communicates directly with the EJB's on the back-end servers. It was written in NetBeans Platform and uses the WebSphere application client library to establish communication with the EJB's. The really painful bit was getting the client to use secure JAAS/SSL communications. But, after that was resolved, we've found that the rich client has a number of advantages over the web-based portal client applications we've become accustomed to: Enormous performance advantage (CORBA vs. HTTP, cut out the Portal Server middle man) Development is simplified and faster due to use of NetBeans' visual designer and Swing's generally robust architecture The debug cycle is shortened by not having to deploy your client application to a test server No mishmash of technologies as with web-based development (Struts, JSF, JQuery, HTML, JSTL etc., etc.) After enduring the pain of web-based development (even JSF) for a while now, I've come to the following conclusion: Rich clients aren't right for every situation, but when you're developing an in-house intranet-based solution, then you'd be crazy not to consider NetBeans Platform or Eclipse RCP. Any comments/experiences with rich clients vs. web clients?

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• How do you host multiple public facing websites on a VPS?

  - by Petras

  We host about 30 websites using typical shared hosting plans using ASP.NET and SQL 2000/2005/2008. I am now wondering about hosting all of these websites using our own virtual private server such as http://www.crystaltech.com/vps.aspx This is clearly cheaper but comes with a lot of questions I need answers to: Is the risk of having to keep this VPS server up and running worth it? Until now, the host provider has managed the server and we have not had to worry about crashes, downtime, software patches etc. We are not server administrators, we are programmers, so this is not really our expertise. On the other hand, it may not be hard to learn. When we make a website live, we log in to a domain management control panel and change the primary and secondary name servers to point to our shared web host: Eg ns1.sharedwebhost.com and ns2.sharedwebhost.com These name servers are going to have to change when we have a VPS. I don’t understand anything about how to set this up. Is there some useful info anyone could direct me to? Or is there software we need to install to make the primary and secondary name servers work on our VPS? The control panel we have for shared hosting comes with DNS management like this: What software would I need to install to create this for each site we host at a VPS? The control panel we have for shared hosting also comes with a POP email interface that allows email addresses to be added easily: Is this something that can be easily set up at a VPS so clients can manage their own email addresses? Is there software we need to install to make this work?

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• Rails.cache throws "marshal dump" error when changed from memory store to memcached store

  - by gsmendoza

  If I set this in my environment config.action_controller.cache_store = :mem_cache_store ActionController::Base.cache_store will use a memcached store but Rails.cache will use a memory store instead: $ ./script/console >> ActionController::Base.cache_store => #<ActiveSupport::Cache::MemCacheStore:0xb6eb4bbc @data=<MemCache: 1 servers, ns: nil, ro: false>> >> Rails.cache => #<ActiveSupport::Cache::MemoryStore:0xb78b5e54 @data={}> In my app, I use Rails.cache.fetch(key){ object } to cache objects inside my helpers. All this time, I assumed that Rails.cache uses the memcached store so I'm surprised that it uses memory store. If I change the cache_store setting in my environment to config.cache_store = :mem_cache_store both ActionController::Base.cache_store and Rails.cache will now use the same memory store, which is what I expect: $ ./script/console >> ActionController::Base.cache_store => #<ActiveSupport::Cache::MemCacheStore:0xb7b8e928 @data=<MemCache: 1 servers, ns: nil, ro: false>, @middleware=#<Class:0xb7b73d44>, @thread_local_key=:active_support_cache_mem_cache_store_local_cache> >> Rails.cache => #<ActiveSupport::Cache::MemCacheStore:0xb7b8e928 @data=<MemCache: 1 servers, ns: nil, ro: false>, @middleware=#<Class:0xb7b73d44>, @thread_local_key=:active_support_cache_mem_cache_store_local_cache> However, when I run the app, I get a "marshal dump" error in the line where I call Rails.cache.fetch(key){ object } no marshal_dump is defined for class Proc Extracted source (around line #1): 1: Rails.cache.fetch(fragment_cache_key(...), :expires_in => 15.minutes) { ... } vendor/gems/memcache-client-1.8.1/lib/memcache.rb:359:in 'dump' vendor/gems/memcache-client-1.8.1/lib/memcache.rb:359:in 'set_without_newrelic_trace' What gives? Is Rails.cache meant to be a memory store? Should I call controller.cache_store.fetch in the places where I call Rails.cache.fetch?

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• Mocking WebResponse's from a WebRequest

  - by Rob Cooper

  I have finally started messing around with creating some apps that work with RESTful web interfaces, however, I am concerned that I am hammering their servers every time I hit F5 to run a series of tests.. Basically, I need to get a series of web responses so I can test I am parsing the varying responses correctly, rather than hit their servers every time, I thought I could do this once, save the XML and then work locally. However, I don't see how I can "mock" a WebResponse, since (AFAIK) they can only be instantiated by WebRequest.GetResponse How do you guys go about mocking this sort of thing? Do you? I just really don't like the fact I am hammering their servers :S I dont want to change the code too much, but I expect there is a elegant way of doing this.. Update Following Accept Will's answer was the slap in the face I needed, I knew I was missing a fundamental point! Create an Interface that will return a proxy object which represents the XML. Implement the interface twice, on that uses WebRequest, the other that returns static "responses". The interface implmentation then either instantiates the return type based on the response, or the static XML. You can then pass the required class when testing or at production to the service layer. Once I have the code knocked up, I'll paste some samples. Thanks Will :)

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• Visual Studio Debugging is not attaching to WebDev.WebServer.EXE

  - by Aaron Daniels

  I have a solution with many projects. On Debug, I have three web projects that I want to start up on their own Cassini ASP.NET Web Development servers. In the Solution Properties - Common Properties - Startup Project, I have Multiple startup projects chosen with the three web applications' Action set to Start. All three web development servers start, and all three web pages load. However, Visual Studio is only attaching to two of the WebDev.WebServer.EXE processes. I have to manually go attach to the third process in order to debug it with the debugger. This behavior just started happening, and I'm at a loss as to how to troubleshoot this. Any help is appreciated. EDIT: Also to note, I have stopped and restarted the development servers several times with no change in behavior. Also, when attaching to the process manually, I see that the Type property of the two automatically attached WebDev.WebServer.EXE processes is Managed, while the Type property of the unattached WebDev.WebServer.EXE process is TSQL, Managed, x86. When looking at the project's properties, however, I am targeting AnyCPU, and do NOT have SQL Server debugging enabled. EDIT: Also to note, the two projects that attach correctly are C# web applications. <ProjectTypeGuids>{349c5851-65df-11da-9384-00065b846f21};{fae04ec0-301f-11d3-bf4b-00c04f79efbc}</ProjectTypeGuids> The project that is not attaching correctly is a VB.NET web application. <ProjectTypeGuids>{349c5851-65df-11da-9384-00065b846f21};{F184B08F-C81C-45F6-A57F-5ABD9991F28F}</ProjectTypeGuids> EDIT: Also to note, the behavior is the same on another workstation. So odds are that it's not a machine specific problem.

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• Rails - difference between config.cache_store and config.action_controller.cache_store?

  - by gsmendoza

  If I set this in my environment config.action_controller.cache_store = :mem_cache_store ActionController::Base.cache_store will use a memcached store but Rails.cache will use a memory store instead: $ ./script/console >> ActionController::Base.cache_store => #<ActiveSupport::Cache::MemCacheStore:0xb6eb4bbc @data=<MemCache: 1 servers, ns: nil, ro: false>> >> Rails.cache => #<ActiveSupport::Cache::MemoryStore:0xb78b5e54 @data={}> In my app, I use Rails.cache.fetch(key){ object } to cache objects inside my helpers. All this time, I assumed that Rails.cache uses the memcached store so I'm surprised that it uses memory store. If I change the cache_store setting in my environment to config.cache_store = :mem_cache_store both ActionController::Base.cache_store and Rails.cache will now use the same memory store, which is what I expect: $ ./script/console >> ActionController::Base.cache_store => #<ActiveSupport::Cache::MemCacheStore:0xb7b8e928 @data=<MemCache: 1 servers, ns: nil, ro: false>, @middleware=#<Class:0xb7b73d44>, @thread_local_key=:active_support_cache_mem_cache_store_local_cache> >> Rails.cache => #<ActiveSupport::Cache::MemCacheStore:0xb7b8e928 @data=<MemCache: 1 servers, ns: nil, ro: false>, @middleware=#<Class:0xb7b73d44>, @thread_local_key=:active_support_cache_mem_cache_store_local_cache> However, when I run the app, I get a "marshal dump" error in the line where I call Rails.cache.fetch(key){ object } no marshal_dump is defined for class Proc Extracted source (around line #1): 1: Rails.cache.fetch(fragment_cache_key(...), :expires_in => 15.minutes) { ... } vendor/gems/memcache-client-1.8.1/lib/memcache.rb:359:in 'dump' vendor/gems/memcache-client-1.8.1/lib/memcache.rb:359:in 'set_without_newrelic_trace' What gives? Is Rails.cache meant to be a memory store? Should I call controller.cache_store.fetch in the places where I call Rails.cache.fetch?

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• How to know about MySQL 'refused connections'

  - by celalo

  Hello, I am using MONyog to montitor my two mysql servers. I get alert emails from MONyog when something goes wrong. There is an error I could not find out why. It says: Connection History: Percentage of refused connections) - 66.67% the percentage is not important, this is just about having refused connections. I get this email every half an hour. So this is like a constant situation. This must be my mistake, because I just set up those servers and there is no chance somebody else could be interfering the servers. MONyog advices me: Try to isolate users/applications that are using an incorrect password or trying to connect from unauthorized hosts. A client will be disallowed to connect if it takes more than connect_timeout seconds to connect. Set the value of log_warnings system variable to 2. This will force the MySQL server to log further information about the error. I added log_warnings=2 to my.cnf and I enabled logging like this: [mysqld_safe] . . log_warnings=2 log-error = /var/log/mysql/error.log . . . . [mysqld_safe] . log-error=/var/log/mysqld.log . . I cannot see any warnings at /var/log/mysql/error.log I can see some warnings at /var/log/mysqld.log but they are about something else. In sum, my question is how can I detect refused connections? Please let me know if any more info is required. Thanks in advance.

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• How can I disable keep-alive on ASP.NET Web Service client requests?

  - by Matthew Brindley

  I have a few web servers behind an Amazon EC2 load balancer. I'm using TCP balancing on port 80 (rather than HTTP balancing). I have a client polling a Web Service (running on all web servers) for new items every few seconds. However, the client seems to stay connected to one server and polls that same server each time. I've tried using ServicePointManager to disable KeepAlive, but that didn't change anything. The outgoing connection still had its "connection: keep-alive" HTTP header, and the server kept the TCP connection open. I've also tried adding an override of GetWebRequest to the proxy class created by VS, which inherits from SoapHttpClientProtocol, but I still see the keep-alive header. If I kill the client's process and restart, it'll connect to a new server via the load balancer, but it'll continue polling that new server forever. Is there a way to force it to connect to a random server each time? I want the load from the one client to be spread across all of the web servers. The client is written in C# (as is the server) and uses a Web Reference (not a Service Reference), which points to the load balancer.

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• Flow control in a batch file

  - by dboarman-FissureStudios

  Reference Iterating arrays in a batch file I have the following: for /f "tokens=1" %%Q in ('query termserver') do ( if not ERRORLEVEL ( echo Checking %%Q for /f "tokens=1" %%U in ('query user %UserID% /server:%%Q') do (echo %%Q) ) ) When running query termserver from the command line, the first two lines are: Known ------------------------- ...followed by the list of terminal servers. However, I do not want to include these as part of the query user command. Also, there are about 4 servers I do not wish to include. When I supply UserID with this code, the program is promptly exiting. I know it has something to do with the if statement. Is this not possible to nest flow control inside the for-loop? I had tried setting a variable to exactly the names of the servers I wanted to check, but the iteration would end on the first server: set TermServers=Server1.Server2.Server3.Server7.Server8.Server10 for /f "tokens=2 delims=.=" %%Q in ('set TermServers') do ( echo Checking %%Q for /f "tokens=1" %%U in ('query user %UserID% /server:%%Q') do (echo %%Q) ) I would prefer this second example over the first if nothing else for cleanliness. Any help regarding either of these issues would be greatly appreciated.

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• java distributed cache for low latency, high availability

  - by Shahbaz

  I've never used distributed caches/DHTs like memcached, jboss cache, ehcache, etc. I'm wondering which, if any, is appropriate for my use. First, I'm not doing web applications (as most of these project seem to be geared towards web apps). I write servers (Order Management Systems actually) for financial trading firms. The servers themselves are not too complicated. They need to receive information (market data, orders, executions, etc.) rout them to their destination while possibly transforming some of these messages. I am looking at these products to solve the following problems: * Safe repository of the state of the server. I'd rather build the logic of my application as a bunch of transformers (similar to Apache Camel) and store the state in a 'safe' place * This repository should be distributed: in case one of these data stores crashes, one or two more should be up and I should be able to switch to them seamlessly * This repository should be fast. Single digits milliseconds count here, in other words, systems which consume/process this data are automated systems, not humans clicking on links. This system needs to have high-throughput and low latency. By sending my data outside the process, I am necessarily slowing performance, but I am trying to balance absolute raw speed and absolute protection of data. * This repository should be safe. Similar to the point about several on-line backups, this system needs to write data to disk (potentially more than one disk). I'd really like to stop writing my own 'transaction servers.' Am I correct to be looking into projects such as jboss cache, ehcache, etc.? Thanks

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• Virtual Lan on the Cloud -- Help Confirm my understanding?

  - by marfarma

  [Note: Tried to post this over at ServerFault, but I don't have enough 'points' for more than one link. Powers that be, move this question over there.] Please give this a quick read and let me know if I'm missing something before I start trying to make this work. I'm not a systems admin professional, and I'd hate to end up banging my head into the wall if I can avoid it. Goals: Create a 'road-warrior' capable star shaped virtual LAN for consultants who spend the majority of their time on client sites, and who's firm has no physical network or servers. Enable CIFS access to a cloud-server based installation of Alfresco Allow Eventual implementation of some form of single-sign-on ( OpenLDAP server ) access to Alfresco and other server applications implemented in the future Given: All Servers will live in the public internet cloud (Rackspace Cloud Servers) OpenVPN Server will be a Linux disto, probably Ubuntu 9.x, installed on same server as Alfresco (at least to start) Staff will access server applications and resources from client sites, hotels, trains, planes, coffee shops or their homes over various ISP, using their company laptops or personal home desktops. Based on my Research thus far, to accomplish this, I'll need: OpenVPN with Bridging Enabled to create a star shaped "virtual" LAN http://openvpn.net/index.php/open-source/documentation/miscellaneous/76-ethernet-bridging.html A Road Warrior Network Configuration, as described in this Shorewall article (lower down the page) http://www.shorewall.net/OPENVPN.html Configure bridge addressesing (probably DHCP) http://openvpn.net/index.php/open-source/faq.html#bridge-addressing Configure CIFS / Samba to accept VPN IP address http://serverfault.com/questions/137933/howto-access-samba-share-over-vpn-tunnel Set up Client software, with keys configured for access (potentially through a OpenVPN-Sa client portal) http://www.openvpn.net/index.php/access-server/download-openvpn-as/221-installation-overview.html

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• HELP!!! Upgrading to windows 2008 R2 server has caused major issue with screen scraping remote serve

  - by bobsov534

  I have three servers. One is Windows 2003(A) and another is Windows 2008(B) and third one is also Windows 2008 (C). All of them are web servers. A and B contains classic asp pages and they are 32 bit servers and C contains asp.net pages and is 64 bit server. The asp pages of A and B use the screen scraping technology to render the asp.net pages from C. When A is ran, the asp.net page is rendered fine, meaning there are no broken images or file not found error. When B is ran, the images appears to be broken because its looking for those images in Server B instead of Server C itself. I believe this issue is caused by IIS 7 or 7.5 since IIS 6 has no problem scraping the remote server pages. Can you please help me with solution to this problem? This is sort of urgent since upgrading to windows server 2008 R2 now has been a major show stopper for us at the moment. Thanks in advance.

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• Automatic Deployment to Multiple Production Environments

  - by Brandon Montgomery

  I want to update an ASP .NET web application (including web.config file changes and database scripts) to multiple production environments - ideally with the click of a button. I do not have direct network connectivity to any of them. I think this means the application servers will have to "pull" the information required for updating the application, and run a script to update the application that resides on the server. Basically, I need a way to "publish" an update, and the servers see that update and automatically download and run it. I've thought about possibly setting up an SFTP server for publishing updates, and developing a custom tool which is installed on production environments which looks at the SFTP server every day and downloads application files if they are available. That would at least get the required files onto the servers, and I could use xcopy/robocopy and Migrator.NET to deploy the updates. Still not sure about config file changes, but that at least gets me somewhere. Is there any good solution for this scenario? Are there any tools that do this for you?

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• Commercial Website architecture question

  - by Maxime ARNSTAMM

  Hello everyone, I have to write an architecture case study but there are some things that i don't know, so i'd like some pointers on the following : The website must handle 5k simultaneous users. The backend is composed by a commercial software, some webservices, some message queues, and a database. I want to recommend to use Spring for the backend, to deal with the different elements, and to expose some Rest services. I also want to recommend wicket for the front (not the point here). What i don't know is : must i install the front and the back on the same tomcat server or two different ? and i am tempted to put two servers for the front, with a load balancer (no need for session replication in this case). But if i have two front servers, must i have two back servers ? i don't want to create some kind of bottleneck. Based on what i read on this blog a really huge charge is handle by one tomcat only for the first website mentionned. But i cannot find any info on this, so i can't tell if it seems plausible. If you can enlight me, so i can go on in my case study, that would be really helpful. Thanks :)

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• How to store a file on a server(web container) through a Java EE web application?

  - by Yatendra Goel

  I have developed a Java EE web application. This application allows a user to upload a file with the help of a browser. Once the user has uploaded his file, this application first stores the uploaded file on the server (on which it is running) and then processes it. At present, I am storing the file on the server as follows: try { FormFile formFile = programForm.getTheFile(); // formFile represents the uploaded file String path = getServlet().getServletContext().getRealPath("") + "/" + formFile.getFileName(); System.out.println(path); file = new File(path); outputStream = new FileOutputStream(file); outputStream.write(formFile.getFileData()); } where, the formFile represents the uploaded file. Now, the problem is that it is running fine on some servers but on some servers the getServlet().getServletContext().getRealPath("") is returning null so the final path that I am getting is null/filename and the file doesn't store on the server. When I checked the API for ServletContext.getRealPath() method, I found the following: public java.lang.String getRealPath(java.lang.String path) Returns a String containing the real path for a given virtual path. For example, the path "/index.html" returns the absolute file path on the server's filesystem would be served by a request for "http://host/contextPath/index.html", where contextPath is the context path of this ServletContext. The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns null if the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a .war archive). So, Is there any other way by which I can store files on those servers also which is returning null for getServlet().getServletContext().getRealPath("")

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• How to display my server's current response time to an average user

  - by Jason

  Sorry, I'm not really sure of the right way to ask this one so bear with me... We have a web application that runs on a set of servers at a data center (not in our offices) We want to be able to somehow 'advertise' to our clients/users that the availability or response time of our servers has met a standard throughout the day. I am being asked to come up with a standard metric that we can easily advertise on our login screen that shows current "standard response time" checked every x minutes. My thinking is that I need to capture something like the results of a traceroute from a server (either in our office, amazon, etc..) to one of the data center servers and come up with a Red/Yellow/Green type of a notifier for the login screen to let the user know that our tests are responding normally and if they are having delay issues it could be their network or connection to the internet. We have lots of clients in rural areas that have poor connectivity and we are trying to let them know any slowness might be on their end, not ours. I've got the LAMP stack to work with, but this could also be some other system all together as long as it can update the main server with the results. I already have pingdom reports that are available, but that's a bit more than people want to read sometimes. Any ideas on what I can do?

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• Analyze log files from many languages using a single tool. And recommendations of logging frameworks

  - by Binary255

  We have a system build on lots of languages. The ones we are interested in logging, in order of priority, are: C/C++ PHP C# Bash Java Wish list: If it is possible, we would like logging to be achieved from the above languages in such a way that we may use a single log viewing tool for all of them. Ideally they would be in the same format, but next to that in as few formats as possible and readable from as many log file viewers as possible. If it is possible logging to a single log file or a set of log files would be nice. With a possibility to filter based on the source language that is being logged. We would like to copy the log files (or should be log to a database and copy it instead?) from multiple servers to a single location. So that we can analyze the log files from many servers at the same time (to see if any of our servers execute a certain piece legacy code for example). Being able to change logging level at runtime would be nice. Thank you for reading! It's quite a complex problem, I hope someone has wrestled with it before and has some valuable information!

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• Creating collaborative whiteboard drawing application

  - by Steven Sproat

  I have my own drawing program in place, with a variety of "drawing tools" such as Pen, Eraser, Rectangle, Circle, Select, Text etc. It's made with Python and wxPython. Each tool mentioned above is a class, which all have polymorphic methods, such as left_down(), mouse_motion(), hit_test() etc. The program manages a list of all drawn shapes -- when a user has drawn a shape, it's added to the list. This is used to manage undo/redo operations too. So, I have a decent codebase that I can hook collaborative drawing into. Each shape could be changed to know its owner -- the user who drew it, and to only allow delete/move/rescale operations to be performed on shapes owned by one person. I'm just wondering the best way to develop this. One person in the "session" will have to act as the server, I have no money to offer free central servers. Somehow users will need a way to connect to servers, meaning some kind of "discover servers" browser...or something. How do I broadcast changes made to the application? Drawing in realtime and broadcasting a message on each mouse motion event would be costly in terms of performance and things get worse the more users there are at a given time. Any ideas are welcome, I'm not too sure where to begin with developing this (or even how to test it)

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• Random problem connecting to MySQL

  - by CharlesLeaf

  Environment: RHEL 5 servers, MySQL 5.1.43, PHP 5.1.6 (using MySQLi). Currently only available within our internal VPN network. Servers ServerA: Webserver ServerB/C/D: Database server (1 master 2 slaves) The error (on ServerA) [Tue May 25 11:12:17 2010] [error] [client CLIENTIP] PHP Warning: mysqli::real_connect() [function.mysqli-real-connect]: (HY000/2003): Can't connect to MySQL server on 'ServerB' (4) in /home/**/Database.php on line 67, referer: [website] Problem description It appears that at completely random times, our website is unable to connect to one of the MySQL servers - usually the Master. Except for the forementioned error message, there is nothing to be found in any of the logs as far as I can see, and most of the times the connection is succesful and everything works as it should. It's just at completely random times, this error pops up. There's no firewall blocking any internal traffic, timeout value is 3 but it doesn't take 3 seconds before it fails to connect. With the default mysql client I can connect from ServerA to ServerB,C and D and haven't encountered a problem yet. Does anyone have a clue what I might be overlooking / could be the problem? Because I've run out of ideas myself.

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• Determine asymmetric latencies in a network

  - by BeeOnRope

  Imagine you have many clustered servers, across many hosts, in a heterogeneous network environment, such that the connections between servers may have wildly varying latencies and bandwidth. You want to build a map of the connections between servers my transferring data between them. Of course, this map may become stale over time as the network topology changes - but lets ignore those complexities for now and assume the network is relatively static. Given the latencies between nodes in this host graph, calculating the bandwidth is a relative simply timing exercise. I'm having more difficulty with the latencies - however. To get round-trip time, it is a simple matter of timing a return-trip ping from the local host to a remote host - both timing events (start, stop) occur on the local host. What if I want one-way times under the assumption that the latency is not equal in both directions? Assuming that the clocks on the various hosts are not precisely synchronized (at least that their error is of the the same magnitude as the latencies involved) - how can I calculate the one-way latency? In a related question - is this asymmetric latency (where a link is quicker in direction than the other) common in practice? For what reasons/hardware configurations? Certainly I'm aware of asymmetric bandwidth scenarios, especially on last-mile consumer links such as DSL and Cable, but I'm not so sure about latency. Added: After considering the comment below, the second portion of the question is probably better off on serverfault.

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• Migrating MachineKey from iis6 on old server to iis7 on new server

  - by MaseBase

  I am migrating our hosting environment to a totally new data center with new boxes and hardware and software... the whole deal. Our website cookies are encrypted using the machineKey, so when I make a request to my domain and point it to the new web server (by overriding the local hosts file), I get an error because the cookie cannot be decrypted, since the Machine Key is different. I'd like to avoid any problems a frequent user might have when they arrive at the new server for the first time. To the best of my knowledge, at this point I think I need to set the same MachineKey from our current servers on our new servers. This way when past visitors with a cookie arrive at our website served by the new server, the cookie will be decrypted properly with the MachineKey it was encrypted with and then log them in properly. My question is where do I find my MachineKey value (in IIS 6 win2k3 server) so I can use that value to set it statically on my new servers? I've pulled up my machine.config file, but it doesn't specify the key, it only specifies a configSection where the key can be defined. It's not in my web.config for the app or elsewhere. I did find this great article on some MachineKey and Web Garden woes (which could explain some other bugs I've been experiencing with regard to the machineKey). Update I am back to this issue and am still faced with a similar problem. I have the MachineKey auto-generated on the IIS6 server but I need to get that exact key so I can set it explicitly and not have it auto-generated anymore. Any help is appreciated...

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• How to skip certain tests with Test::Unit

  - by Daniel Abrahamsson

  In one of my projects I need to collaborate with several backend systems. Some of them somewhat lacks in documentation, and partly therefore I have some test code that interact with some test servers just to see everything works as expected. However, accessing these servers is quite slow, and therefore I do not want to run these tests every time I run my test suite. My question is how to deal with a situation where you want to skip certain tests. Currently I use an environment variable 'BACKEND_TEST' and a conditional statement which checks if the variable is set for each test I would like to skip. But sometimes I would like to skip all tests in a test file without having to add an extra row to the beginning of each test. The tests which have to interact with the test servers are not many, as I use flexmock in other situations. However, you can't mock yourself away from reality. As you can see from this question's title, I'm using Test::Unit. Additionally, if it makes any difference, the project is a Rails project.

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