Multiple participants collaborate in a distributed system.

How one know that another participant is working properly and is ready to receive messages?

• A central participant Could ping each system periodically in with a Asynchronous Request-Response conversation. If a valid response is returned, the component is "alive". This request would not be a "regular" request, but an out-of-band request that retrieves the component's status.
• The disadvantage of this solution is that monitoring depends on a single component making requests, which in itself can become a point of failure. The system also sends up sending a lot of unnecessary request messages.
• Polling the components also assumes a central monitoring entity is aware of all components' identities. In a loosely coupled system, where components come and go, this may not be a valid assumption. Components would have to register so they can be pinged.

The component supplies a Heartbeat, a series of periodic messages that indicate the component is operating well.

The Heartbeat conversation involves the following participants:

• The Component sends periodic Heartbeat messages.
• The Observer detects when the heartbeat is missing and triggers an alert or corrective action.

Related patterns: Asynchronous Request-Response