- Creation of sessions - when a session is created, the session gets replicated
- Attributes added to the session - the session values get replicated to the other nodes in the cluster
- Attributes removed from the session - the value will get removed from the replicas too
What is session replication in Linux?
Session Replication. Session replication is a mechanism used to replicate the data stored in a session across different instances. However, the replicated instance must be part of the same cluster. When session replication is enabled in a cluster environment, the entire session data is copied on a replicated instance.
How does the web server determine whether session data is copied?
At the end of a web request, the Web Server determines whether the session data needs to be copied through the session replication configuration that is stored in the server configuration file, the server.xml. Consider a use case of four instances forming a cluster with session replication enabled on the Administration Server.
What is Tomcat web session replication?
What is Tomcat web session replication? Apache Tomcat is a lightweight, highly flexible open-source project developed by the Apache Software Foundation that offers a "pure Java" HTTP web server environment for running Java code. Major companies such Walmart, E-Trade, and The Weather Channel have all used Tomcat to build powerful, robust websites.
What happens to session data when server crashes?
If an application server crashes, replicating web session data prevents you from losing the web sessions that were stored on that server. Apache Tomcat includes built-in functionality for web session replication, helping to preserve data in the event of an unexpected failure.
What is session replication in Tomcat?
Tomcat provides in-memory session replication through a combination of serializable session attributes, "sticky sessions", which are provided by the load balancer, and specialized components configured in Tomcat's XML configuration files. We'll tackle each of these components one by one.
What is session replication in WebLogic?
When in-memory replication is enabled for a web application, WebLogic Server copies session state from one server in the cluster (primary) to one other server in the same cluster (secondary). The replica on the secondary server is kept up-to-date so that it may be used if the primary server fails.
What is session failover?
Session failover ensures that session data remains accessible to OpenSSO Enterprise servers and OpenSSO Enterprise Policy Agents. Service requests are routed to a failover server, the user's session continues uninterrupted, and no user data is lost.
What is the session clustering?
Web session clustering provides freedom of load balancing user sessions to any app server without losing intermediate user session data. Why? Because underneath it takes advantage of in-memory distributed caching technology which ensures that user sessions are available in memory regardless of which server is hit.
Which of the following is a high availability cluster where sessions are not lost when a single application server goes offline or is otherwise unreachable?
A concept used in a High Availability Cluster where sessions are not lost when a single application server goes offline, or is otherwise unreachable.
What is spring session?
Spring Session provides an API and implementations for managing a user's session information while also making it trivial to support clustered sessions without being tied to an application container-specific solution.
When clustering servlets you should avoid storing values in ServletContext?
If your clustering your servlets, then one of the considerations is not to store any state in your ServletContext. Avoid storing values in a ServletContext. A ServletContext is not serializable and also the different instances may exist in different JVMs.
Let's take an example based on Spring-Session project
This guide describes how to use Spring Session to transparently leverage Redis to back a web application’s HttpSession with Java Configuration.
Updating Dependencies
Before you use Spring Session, you must ensure to update your dependencies. If you are using Maven, ensure to add the following dependencies: pom.xml
Spring Java Configuration
After adding the required dependencies, we can create our Spring configuration. The Spring configuration is responsible for creating a Servlet Filter that replaces the HttpSession implementation with an implementation backed by Spring Session. Add the following Spring Configuration:
Java Servlet Container Initialization
Our Spring Configuration created a Spring Bean named springSessionRepositoryFilter that implements Filter. The springSessionRepositoryFilter bean is responsible for replacing the HttpSession with a custom implementation that is backed by Spring Session.
httpsession Sample Application
You can run the sample by obtaining the source code and invoking the following command:
What is Tomcat web session replication?
A web session refers to the length of time that a user spends browsing a website, as well as the activities they perform on the website and the data they generate during the session. Applications save this data in order to remember and better serve the users who visit a website: for example, by personalizing their experiences, or by storing the items they want to purchase in a digital "shopping cart."
What is session replication?
Session replication is just one part of web session clustering, in which user sessions are balanced among the different nodes in a cluster. If a single node fails or needs to be shut down for maintenance, web session replication and web session clustering ensure that the entire system recovers seamlessly. In particular, the users whose data is stored on the node should not experience any downtime or disruption.
What is readmode in Tomcat?
The readMode attribute specifies how to store session attributes. The MEMORY mode, which is the default, stores attributes in both Redis and the local Tomcat session. The REDIS mode stores attributes only in Redis.
What is update mode in Redis?
The updateMode attribute specifies how to update session attributes. The DEFAULT mode stores session attributes in Redis only with the setAttribute () method. The AFTER_REQUEST mode stores session attributes in Redis after each request.
What companies use Tomcat?
Major companies such Walmart, E-Trade, and The Weather Channel have all used Tomcat to build powerful, robust websites. If you're building a website with Apache Tomcat, you might run into an issue called "Tomcat web session replication.".
Can Redisson be used with Tomcat?
The good news is that Redisson makes it easy to perform Tomcat web session replication in Redis, as well as including other useful features such as different caching implementations and MapReduce programming. The RedissonSessionManager class has been specifically designed for use with Apache Tomcat, so that you can store Tomcat sessions in a Redis database.
Is Redis a Java language?
However, Redis isn't automatically compatible with programming languages such as Java out of the box. Since Tomcat is designed specifically for Java, this fact can pose a challenge if you want to perform Tomcat web session replication in Redis.
