About intra-system communications

Within a system, the VCS engine (VCS High Availability Daemon) uses a VCS-specific communication protocol known as Inter Process Messaging (IPM) to communicate with the GUI, the command line, and the agents.

Figure: Basic communication on a single VCS system shows basic communication on a single VCS system. Note that agents only communicate with High Availability Daemon (HAD) and never communicate with each other.

Figure: Basic communication on a single VCS system

Basic communication on a single VCS system

Figure: Communication from a single agent to HAD depicts communication from a single agent to HAD.

Figure: Communication from a single agent to HAD

Communication from a single agent to HAD

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 system. 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.