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active/active – In an active/active cluster, the master node or nodes manages write transactions while the standby nodes are available for read requests. Streaming Replication with hot standby or EDB Postgres Multi-Master Replication manage active/active clusters. If you are using an active/active replication scenario, you probably have a PEM agent on each node of the cluster, and are actively monitoring each node with PEM.
active/passive – In an active/passive cluster, only the master node is used for read and write transactions. Standby nodes ensure that in the event of a failure of the master node, a complete backup is available to replace the master node. RHCS (Red Hat Cluster Suite), Veritas Replicator, or Streaming Replication without hot standby manage active/passive clusters. If you are using an active/passive replication scenario, you are probably only actively monitoring the master node of your replication scenario with PEM.
To enable takeover of a server, right-click on the name of a server in the PEM client tree control, and select Properties from the context menu. When the Properties dialog opens, check the box next to Allow takeover? on the PEM Agent tab of the Server Properties dialog. Each server that will potentially be promoted to the role of Master should be configured to allow takeover by another agent.
To instruct the agent to takeover the monitoring of a server, the failover process must create a file in a special flag directory which will instruct the agent to take responsibility for the specified server. By default, the flag directory used by the agent is:
Where $TMPDIR is the temporary directory for the user account under which the agent runs.
The user account is usually root on a Linux system or Administrator on Windows. You can override the directory path by specifying a value for the AgentFlagDir configuration option in the registry on Windows, or in the agent_flag_dir parameter in the agent configuration file on Linux.
touch /tmp/pem/agent-agent_id/takeover-server-server_id
agent_id is the numeric identifier of the agent that should takeover the monitoring of the server
server_id is the numeric identifier of the server that will be taken over.
To find the agent_id and server_id, log into the PEM client, and highlight the name of the agent or server; the numeric identifier will be displayed in the ID row on the Properties pane of the PEM client.


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