Node Agents

A node agent is a lightweight process that runs on every machine that hosts server instances, including the machine that hosts the DAS. The node agent:

• Starts and stops server instances as instructed by the DAS.

• Restarts failed server instances.

• Provides a view of the log files of failed servers and assists in remote diagnosis

• Synchronizes each server instance’s local configuration repository with the DAS’s central repository, as it starts up the server instances under its watch.

• When an instance is initially created, creates directories the instance needs and synchronizes the instance’s configuration with the central repository.

• Performs appropriate cleanup when a server instance is deleted.

Each physical host must have at least one node agent for each domain to which the host belongs. If a physical host has instances from more than one domain, then it needs a node agent for each domain. There is no advantage of having more than one node agent per domain on a host, though it is allowed.

Because a node agent starts and stops server instances, it must always be running. Therefore, it is started when the operating system boots up. On Solaris and other Unix platforms, the node agent can be started by the inetd process. On Windows, the node agent can be made a Windows service.

For more information on node agents, see Chapter 7, Configuring Node Agents, in Sun Java System Application Server 9.1 High Availability Administration Guide.