Collective architecture
The set of Liberty servers in a single management domain is called a collective. A collective consists of at least one server with the collectiveController-1.0 feature enabled that is called a collective controller. Optionally, a collective can have many servers with the collectiveMember-1.0 feature enabled that are called collective members and a collective can be configured to have many collective controllers.


The collective controller provides for a centralized administrative control point to perform operations such as MBean routing, file transfer, and cluster management. A core role of collective controllers is to receive information, such as MBean attributes and operational state, from the members within the collective so that the data can be retrieved readily without having to invoke an operation on each individual member.

A set of collective controllers is called a replica set. There is only one replica set per collective, and all controllers must be part of the replica set. When there is more than one collective controller, each collective controller replicates its data to the other collective controllers in the replica set to allow for high availability and data protection. The replica set is logically present even when only one controller is in use. When changing your configuration to multiple replicas in a set, include at least three replicas in the set. The controllers in the replica set communicate with each other using a collaboration scheme to ensure that data is replicated across the set of controllers no matter which controller in the set receives an operation to store data. Each controller has a dedicated port for use by the replication protocol. Communication between the controllers in the replica set is always authenticated and protected with SSL.
A collective member can be configured with multiple collective controller endpoints. A collective member only communicates with one collective controller at a time; however, a configuration with more than one collective controller endpoint provides failover and workload balancing. Member-to-controller communication is always in the form of MBean operations that are performed over the IBM® JMX Rest Connector. Communication between controllers and members is always authenticated and protected with SSL.
See Setting up the server-management environment for Liberty by using collectives for more information.
Configured and standby replicas
Replicas that have been added to a configured replica set are running (active replicas) or stopped (inactive replicas). A replica that is started and that has never been added to a configured replica set, or was removed from a configured replica set, is called a standby replica.

Summary of collective architecture terms
- collective
- The set of Liberty servers in a single management domain.
- collective controller
- A server that has the collectiveController-1.0 feature enabled.
- collective member
- A server that has the collectiveMember-1.0 feature enabled.
- replica set
- A set of collective controllers. For optimal functionality and high availability, a replica set must have at least three controllers.
- replica port
- A dedicated port on a controller that is used by the replication protocol.
- configured replica set
- The union of the active replicas and inactive replicas.
- active replicas
- The started replicas that have been added to the configured replica set.
- inactive replicas
- The stopped replicas that have been added to the configured replica set.
- standby replica
- The started replicas that have not been added to the configured replica set or that were removed from the configured replica set.