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1.2. Components

The Heartbeat messaging layer comprises several interlocking but distinct components.

1.2.1. Communication module

The Heartbeat communication module provides strongly authenticated,locally-ordered multicast messaging over basically any media, IP-based or not. Heartbeat supports cluster communications over the following network link types:
  • unicast UDP over IPv4;
  • broadcast UDP over IPv4;
  • multicast UDP over IPv4;
  • serial link communications.

Warning

Please consider some important caveats with regard to serial link connectivity (see ). As a general rule: when in doubt, serial links should be avoided.
Heartbeat can detect node failure reliably in less than a half-second. It will register with the system watchdog timer if configured to do so.
The heartbeat layer has an API which provides the following classes of services:
  • intra-cluster communication - sending and receiving packets to cluster nodes
  • configuration queries
  • connectivity information (who can the current node hear packets from) - both for queries and state change notifications
  • basic group membership services