HTTP session memory-to-memory replication

 HTTP session memory-to-memory replication is a technique used in web applications to ensure high availability and fault tolerance of user sessions. In a typical web application, the user's session data (such as login information, shopping cart contents, preferences, etc.) is stored in memory on the server-side. However, if the server hosting the user's session goes down or becomes unreachable, the session data will be lost, and the user will have to start a new session.

To address this issue, session replication mechanisms are employed to duplicate or synchronize the session data across multiple servers. One such mechanism is memory-to-memory replication. In this approach, the session data is copied or shared between multiple servers' memory. If one server fails, another server can take over the processing of the user's session since it has access to the same session data.

Here's how memory-to-memory replication typically works:

  1. Cluster of Servers: The web application is deployed on a cluster of servers. These servers can be physical machines or virtual machines, and they are part of a group (cluster) that works together to provide the application's functionality.


  3. Session Data Replication: When a user's session is created or modified on one server within the cluster, the updated session data is replicated (copied or shared) to all the other servers in the cluster. This is typically achieved using a distributed caching mechanism or an in-memory data grid.


  5. Load Balancer: A load balancer is used to distribute incoming requests from users across the servers in the cluster. The load balancer ensures that each server receives a fair share of the traffic and prevents any single server from being overloaded.


  7. High Availability: If one of the servers fails, the load balancer can redirect the user's requests to any other server in the cluster, and since the session data is replicated across all servers, the user's session can be seamlessly continued on another available server without any data loss.


  9. Session Affinity: To ensure that all requests from a specific user during a session are routed to the same server where their session data is stored, the load balancer may use techniques like session affinity or sticky sessions.

HTTP session memory-to-memory replication is especially valuable in scenarios where session data is crucial to the user's experience and should not be lost due to server failures. It enhances the overall reliability and fault tolerance of web applications, contributing to a smoother and more consistent user experience.

To modify the mode setting for a replication domain:

  1. In the administrative console, click Servers > Server Types > WebSphere application servers > server_name.
  2. Under Container settings, click either SIP container settings or Web container settings, and then click Session management > Distributed environment settings > Memory-to-memory replication.
Avoid trouble: If you change any of the replication domain settings for one cluster member, including the mode setting, you should change them for all of the other members of the cluster.
 

Good Luck

Vijayarathinam

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