Network Deployment (Distributed operating systems), v8.0 > Learn about applications > Web applications > Sessions
Memory-to-memory replication
Memory-to-memory session replication is the session replication to another WAS. In this mode, sessions can replicate to one or more Application Servers to address HTTP Session single point of failure (SPOF).
The WAS instance in which the session is currently processed is referred to as the owner of the session. In a clustered environment, session affinity in the WAS plug-in routes the requests for a given session to the same server. If the current owner server instance of the session fails, then the WAS plug-in routes the requests to another appropriate server in the cluster. In a peer-to-peer cluster, the hot failover feature causes the plug-in to failover to a server that already contains the backup copy of the session, avoiding the overhead of session retrieval from another server containing the backup. In a client/server cluster, the server retrieves the session from a server that has the backup copy of the session. The server now becomes the owner of the session and affinity is now maintained to this server.
There are three possible modes to run in:
Server mode Only store backup copies of other WAS instance sessions. Do not send out copies of any session created to other WAS instances. Client mode Only send out copies of sessions owned by WAS instances. Do not receive backup copies of sessions from other WAS instances. Both mode Send out copies of sessions owned by WAS instance. Receive backup copies of sessions from other WAS instances.
We can select the replication mode of server, client, or both when configuring the session management facility for memory-to-memory replication. The default is both. This storage option is controlled by the mode parameter.
The memory-to-memory replication function is accomplished by the creation of a data replication service instance in an application server that talks to other data replication service instances in remote application servers. Configure this data replication service instance as a part of a replication domain. Data replication service instances on disparate application servers that replicate to one another must be configured as a part of the same domain. Configure all session managers connected to a replication domain to have the same topology. If one session manager instance in a domain is configured to use the client/server topology, then the rest of the session manager instances in that domain must be a combination of servers configured as Client only and Server only. If one session manager instance is configured to use the peer-to-peer topology, then all session manager instances must be configured as Both client and server.
For example, a server only instance, and a both client and server instance, cannot exist in the same replication domain. Multiple data replication service instances in a single replication domain must have the same mode.
Examples of memory-to-memory replication configuration:
There is a single replica in a cluster by default. We can modify the number of replicas through the replication domain.
Related
Memory-to-memory topology: Peer-to-peer function
Memory-to-memory topology: Client/server function
Data replication
Replicating data with a multi-broker replication domain