Intra-Node Communication

Within a node, the VCS engine (HAD) uses a VCS-specific communication protocol known as Inter Process Messaging (IPM) to communicate with the GUI, the command line, and the agents. The following illustration shows basic communication on a single VCS node. Note that agents only communicate with HAD and never communicate with each other.

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The following illustration depicts communication from a single agent to HAD.

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The agent uses the Agent framework, which is compiled into the agent itself. For each resource type configured in a cluster, an agent runs on each cluster node. The agent handles all resources of that type. The engine passes commands to the agent and the agent returns the status of command execution. For example, an agent is commanded to bring a resource online. The agent responds back with the success (or failure) of the operation. Once the resource is online, the agent communicates with the engine only if this status changes.