May 12, 1 min read. Floyd Marinescu. Join a community of over , senior developers. View an example. You need to Register an InfoQ account or Login or login to post comments. But there's so much more behind being registered. Terracotta releases free 4 node Tomcat Session Clustering. Like Print Bookmarks.
May 12, 1 min read by Floyd Marinescu. The products can be integrated with Tomcat and WebLogic without any application cod echanges. Terracotta Sessions is based on their distributed shared objects DSO product which uses a hub and spoke architecture and can synchronize changes across nodes at the field level instead of serialization. This same architecture and featureset is now available for free for Tomcat and WebLogic, for cluster deployments of up to four nodes.
The products can thus be used to provide distributed clustering and high availability of HTTPSessions on web farms, but even in situations where sticky-load balancers are in use and no data is being shared, Terracotta sessions can be used to have the 'hub' keep a backup of all data on each node and transparently fail over to another server should one machine go down.
Terracotta's other main product is DSO Distributed Shared Objects , which is a VM clustering software aimed at transparently clustering any object in the VM without any code changes such as serialization. For users behind an Internet proxy, this is made possible by updating tim-get. Now we're back to session replication and failover but the configuration is usable across different application servers. There are 3 basic strategies to manage session failover over cluster nodes.
The first one is not to use session at all: it has major consequences on your development time, since your application has to do it directly.
The second one is to look at the server documentation to look how it is done with a specific server. This ties your session management to a single product. Last but not least, you can use a third-party product. This has the advantage to move the configuration outside the scope of your specific server, thus letting you move with less hassle from one server to the next and still enjoy the benefits of session failover.
Were I a system engineer, this is the solution I would recommend since it is the most flexible. Thanks for visiting DZone today,. Edit Profile. Sign Out View Profile.
Over 2 million developers have joined DZone. Managing Web Sessions. Like 0. Join the DZone community and get the full member experience. Join For Free. Sessions are evil From time to time, I stumble upon articles blaming sessions and labeling them as evil. If you think sessions are evil, some solutions are: Store data in the database: now your data has to go from the front-end to the back-end to be saved, and then back again to be used.
Classic relational database may not be the solution you're looking for. Most high-traffic low-response time take the NoSQL route, although I don't know if they use it for session storage purpose Store data on the client side through cookies: your clients needs to have cookie-enabled browser. Server session replication Another solution is to embrace session - this is a JEE feature after all - but to use session replication in order to avoid session data loss.
Serializable IMHO, these rules should be enforced on all web applications, whether currently deployed on a cluster or not, since they are not very restrictive. However, they are usually based on the following implementations: In memory replication: each server stores all servers session datat. This implementation heavily uses the network and the memory Database persistence File persistence: the file system used should be available to all cluster nodes For our simple example, I will just show you how to use in-memory session replication in Tomcat.
This is validated when starting a second node with the following log in the first: INFO: Replication member added:org. Third party session replication The previous solution has the disadvantage of specific server configuration. In order to set up Terracotta, two steps are mandatory: create the configuration for the server. In order to be used, name it tc-config. In order to see what is stored, you can also launch the Terracotta Developer Console.
Conclusion There are 3 basic strategies to manage session failover over cluster nodes. To go further: Sessions are evil article Another Session are evil article, more finely-shaded Session variables pros and cons Tomcat clustering how-to Terracotta Web session product overview.
Opinions expressed by DZone contributors are their own. Change the tc-config. Note that the tc-config. Other portions of that xml file should remain unchanged. Remember to change the IP address in the example below to the address of the Terracotta Server. Start the Terracotta server specifying the location of the tc-config.
Open Terracotta supports a variety of JVMs and each one requires a unique boot jar be present in the bootclasspath when launching the Geronimo server. It is possible to use other JVMs, though a different boot jar will likely need to be created. You should issue this command on your system to find the arguments that are appropriate for your environment.
This value will be used to determine which Terracotta server will provide the Terracotta client with its tc-config. Alternately, -Dtc. Review the Terracotta documentation for more details. Use the Geronimo admin console to install the appropriate example application to each of the Geronimo installations.
Note that the two applications above are identical except for the field which indicates the Server name e. Server1, Server2. This distinction will be useful when testing. Now test that the applications were deployed correctly by accessing the applications with your favorite Web Browser:.
Now you are ready to setup the Load Balancer. You can test load balancing and failover by requesting the following URL with your favorite Web browser. Of course, replace YourHost with the actual host name or IP address. Note that the output page contains the ID of the server that is servicing the request.
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