Configuring Liberty collective replica sets

You can configure collective replica sets.

• Optional: If necessary, you can modify the default configuration of the initial replica set.

  The configuration of the initial replica set occurs when the initial collective controller is created. If it is necessary to modify the default replica configuration, the following properties can be changed in the server.xml file:

  Optional settings: These values will default but can be altered.

  replicaHost

  Hostname for each individual replica

  replicaPort

  Port for each individual replica

  This is not the http or https port of the collective controller, but it is a unique port that is used for communication between the replicas of the replica set.

  repositoryDir

  Directory location that should be used to store repository data

• Add a replica to an existing replica set.

  During the life of a replica set, it might become necessary to add one or more replicas to an existing set, to increase capacity for example.

  The existing replicas in the replica set do not require any updates to their configuration. You might want to update them so that their configurations in the server.xml files more accurately reflect the replicas forming the replica set, but this is unnecessary and will not affect their behaviors.

  Note: It is not necessary to change the replicaSet value in the server.xml file of an existing replica in the set. No change to the configuration of an existing replica is required. If you do want to update the replicaSet values in the configurations of existing replicas in the set so that the configuration values are consistent across all replicas in the set, you must set the isInitialReplicaSet value in the configurations of the existing replicas to false. This is because after you alter the replicaSet value, it no longer describes the initial replica set—it now describes a changed replica set.

  To add a new replica, follow these steps:

  1. Ensure that the existing replica set is running and that a majority of the replicas are available.
  2. Create a new server that will be the new collective controller.

     wlp\bin\server create MyNewController

  3. Replicate to transform the new server into a collective controller.

     wlp\bin\collective replicate MyNewController 
        --host=<host_of_running_controller>  
        --port=<https_port_of_running_controller> 
        --user=<user_for_running_controller> 
        --password=<user_password> 
        --keystorePassword=<password_for_new_controller>  

  4. Configure the new replica's server.xml file using the replicate command.
     The replicate command will print XML that must be copied into the server.xml file. The replica's configuration can be modified as detailed below.

     • Required setting:
       This value must be explicitly set. The XML printed by the replicate command will contain this configuration and is sufficient for this setting.

       replicaSet

       Space-delimited list containing the host:port for each of the replicaHosts and replicaPorts in the replica set, excluding the values for the collective controller now being added to the set

       For example,

       original.host.com:10001 some.other.host.com:10003

       At least one of the values in this set must already be a replica of the existing replica set.

     • Optional settings:
       These will default but can be altered.

       isInitialReplicaSet

       False

       replicaHost

       Hostname for each individual replica

       replicaPort

       Port for each individual replica

       This is not the http or https port of the collective controller, but it is a unique port that is used for communication between the replicas of the replica set.

       repositoryDir

       Directory location that should be used to store repository data

     Here is an example of what you might add to a new replica's server.xml file:

     <collectiveController replicaHost="localhost" 
        replicaPort="10012" 
        replicaSet="localhost:10010 localhost:10011" 
        isInitialReplicaSet="false"/> 

     The XML printed by the replicate command will require updating the server's security configuration as well as specifying the collectiveRootKeys keystore password. The server's security configuration should be identical to the original collective controller's configuration, and the collectiveRootKeys keystore password should be the password used for the original collective controller's collectiveRootKeys keystore password. If the replica was created from the controller created in Configuring a Liberty collective, the new controller's configuration should contain the following:

     <quickStartSecurity userName="adminUser" userPassword="adminPassword" />
       <!-- collective root signers keystore -->
       <keyStore id="collectiveRootKeys" password="yourPassword"
         location="${server.config.dir}/resources/collective/rootKeys.jks" />

  5. Start the new replica by starting the new collective controller.
  6. Invoke the addReplica operation of the WebSphere:feature=collectiveController,type=RepositoryConfiguration,name=RepositoryConfiguration MBean, passing in the replica endpoint (in the form "replicaHost:replicaPort") of the replica to add.
• Remove a replica from an existing replica set.

  During the life of a replica set, it might become necessary to remove one or more replicas from the set.

  The existing replicas in the replica set do not require any updates to their configuration. You might want to update them so that their configurations in the server.xml files more accurately reflect the replicas forming the replica set.

  Note: It is not necessary to change the replicaSet value int the server.xml file of an existing replica in the set. No change to the configuration of an existing replica is required. If you do want to update the replicaSet values in the configurations of existing replicas in the set so that the configuration values are consistent across all replicas in the set, you must set the isInitialReplicaSet value in the configurations of the existing replicas to false. This is because after you alter the replicaSet value, it no longer describes the initial replica set—it now describes a changed replica set.
  To remove a replica from a set, follow these steps:

  • Ensure the existing replica set is running with a majority of the replicas available.
  • Invoke the removeReplica operation of the WebSphere:feature=collectiveController,type=RepositoryConfiguration,name=RepositoryConfiguration MBean, passing in the replica endpoint (in the form "replicaHost:replicaPort") of the replica to remove.