Multiple machine scaling

Multiple machine scaling

Multiple machine scaling techniques rely on using multiple copies of an application server. The sequence of operations on behalf of a client falls into two categories:

Stateless A server processes requests based solely on information provided with each request and does not rely on information from earlier requests. The server does not need to maintain state information between requests.
Stateful A server processes requests based on both the information provided with each request and information stored from earlier requests. The server needs to access and maintain state information generated during the processing of an earlier request.

The load distribution facilities in the product use several different techniques for maintaining state information between client requests:

Session affinity The load distribution facility recognizes the existence of a client session and attempts to direct all requests within that session to the same server.
Transaction affinity The load distribution facility recognizes the existence of a transaction and attempts to direct all requests within the scope of that transaction to the same server.
Server affinity The load distribution facility recognizes that although multiple servers might be acceptable for a given client request, a particular server is best suited for processing that request.

The session manager, which is part of each application server, stores client session information and takes session affinity and server affinity into account when directing client requests to the cluster members of an application server. The workload management service considers server affinity and transaction affinity when directing client requests among the cluster members of an application server.

Related:

WebSphere Application Server - Clusters
Sessions
Session management support
Task overview: Managing HTTP sessions

Stateless	A server processes requests based solely on information provided with each request and does not rely on information from earlier requests. The server does not need to maintain state information between requests.
Stateful	A server processes requests based on both the information provided with each request and information stored from earlier requests. The server needs to access and maintain state information generated during the processing of an earlier request.

Session affinity	The load distribution facility recognizes the existence of a client session and attempts to direct all requests within that session to the same server.
Transaction affinity	The load distribution facility recognizes the existence of a transaction and attempts to direct all requests within the scope of that transaction to the same server.
Server affinity	The load distribution facility recognizes that although multiple servers might be acceptable for a given client request, a particular server is best suited for processing that request.