Network Deployment (Distributed operating systems), v8.0 > Set up the application serving environment > Balancing workloads > Replicating data across application servers in a cluster
Data replication
Overview
The Data Replication Service (DRS) replicates data, objects, or events among application servers.
- Session manager uses DRS when configured to do memory-to-memory replication. session manager maintains data about sessions across multiple application servers, preventing the loss of session data if a single application server fails.
- Dynamic cache uses DRS to improve performance by copying cache information across application servers in the cluster, eliminating the need to repeatedly perform the same tasks and queries in different application servers.
- Stateful session beans use DRS so that applications using stateful session beans are not limited by unexpected server failures.
When you use the replication services, ensure that the Propagate security attributes option is enabled. Security attribute propagation is enabled, by default.
We can define the number of replicas that DRS creates on remote application servers. A replica is a copy of the data that copies from one application server to another. The number of replicas that you configure affects the performance of the configuration. Smaller numbers of replicas result in better performance because the data does not have to copy many times. However, if you create more replicas, we have more redundancy in the system. By configuring more replicas, the system becomes more tolerant to possible failures of application servers in the system because the data is backed up in several locations.
Define a single replica configuration helps you to avoid a single point of failure in the system. However, if the system must be tolerant to more failure, introduce extra redundancy in the system. Increase the number of replicas that you create for any HTTP session that is replicated with DRS. The Number of replicas property for any replication domain used by the dynamic cache service must be set to Entire domain.
Session manager, dynamic cache, and stateful session beans are the three consumers of replication. A consumer is a component that uses the replication service. When you configure replication, the same types of consumers belong to the same replication domain. For example, if you are configuring both session manager and dynamic cache to use DRS to replicate objects, create separate replication domains for each consumer. Create one replication domain for all the session managers on all the application servers and one replication domain for the dynamic cache on all the application servers. The only exception to this rule is to create one replication domain if you are configuring replication for HTTP sessions and stateful session beans. Configuring one replication domain in this case ensures that the backup state information is located on the same backup application servers. Stateful session bean failover for the EJB container
Memory-to-memory replication
Security attribute propagation
Configure cache replication
Replicating data across application servers in a cluster
CSIv2 inbound communications settings
CSIv2 outbound communications settings