2. Concepts

  • A Message represents data in transit through a system.
  • A Message consists of a payload and optional attributes that describe the payload.
  • Data is transmitted to one or more subscriptions.
  • A Topic is a feed of data.
  • Subscribing Forwarder ensures data delivery. 
  • Subscriptions expresses an interest in receiving messages.
  • Subscriptions register each delivery of data.
  • Subscription determines which subscribers are registered to receive a message and queues up the messages to be sent. 
  • Subscribers can receive data through pull or push.
  • Subscribers receive messages by Pub/Sub, pushing them to the endpoint or by pulling them from the service.
  • Subscribers can be configured to receive messages on a push or pull basis.
  • Publishing Forwarder receives data from the publisher on behalf of the topic.
  • Pull subscribers use HTTPS requests to google APIs.
  • Push subscribers can accept post requests over HTTPS.
  • Push subscribers use webhook endpoints.
  • Pub is short for publishers.
  • Sub is short for subscribers.