Data storage depends on whether the cluster is stateful or stateless.

In both types of clusters, Integration Server stores data from cluster nodes (for example, service results, scheduled tasks, audit data, and documents) in shared database components. For information about database components, see Installing Software AG Products.

In a stateful cluster, the session state for clients connected to cluster nodes is stored in a distributed cache in a Terracotta Server Array. The cache makes state available to all servers in the cluster, which enables multi-step transactions in a conversation to begin on one node in the cluster and continue on other nodes. For example, in the Cross-site Request Forgery (CSRF) Guard feature, a token is created locally on a server and saved in the distributed Terracotta Server Array cache, which makes the token available to all other cluster nodes.

In a stateless cluster, and the session state of a client is not stored in a distributed Terracotta Server Array cache; state is only available locally. Stateless clusters do not support all Integration Server-related features and components (see table below). Stateless clusters require less hardware and less software, and less work is needed for set up and maintenance. However, stateless cluster cannot support multi-step transactions on multiple cluster nodes because state is not available.