Pulse is a message bus: it allows participants to publish messages and other participants to subscribe to those messages. Taskcluster uses this bus to communicate between microservices, notifying interested parties when specific events have occurred. The system is based on AMQP in a publish-subscribe configuration.

All Taskcluster AMQP exchanges are topic exchanges. Message bodies are always JSON, and messages are "copied" to multiple routing keys using the AMQP Cc header.

Usually, we prefix all exchanges from the same component with a common exchangePrefix to ensure uniqueness. For routing keys we strive to always have the same entries for messages on a given exchange and use _ if no value makes sense for the given routing key entry with a specific message.

Each service's reference documentation describes the events the service sends (if any). Each kind of event is sent on a different exchange, and each event has a routing key containing characteristics of the event on which consumers might like to filter.

Pulse is a publicly accessible service, and the pulse message schemas are a part of Taskcluster's published API, so they make a nicely decoupled integration point for external services.