Pub/Sub
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Pub/Sub enables you to create systems of event producers and consumers, called publishers and subscribers.
Publishers send events to the Pub/Sub service, without regard to how or when these events are to be processed. Pub/Sub then delivers events to all services that need to react to them.
Message: the data that moves through the service.
Topic: a named entity that represents a feed of messages.
Subscription: a named entity that represents an interest in receiving messages on a particular topic.
Publisher (also called a producer): creates messages and sends (publishes) them to the messaging service on a specified topic.
Subscriber (also called a consumer): receives messages on a specified subscription
Exponential back-off enables Pub/Sub to use a retry mechanism where Pub/Sub waits 10 seconds before retrying a message
If the message fails, Pub/Sub increases the delay before retrying for the next time. For every retry, Pub/Sub keeps increasing the delay up to a 10-minute interval between retries.
For retention duration, a subscription tries to deliver a message for 7 days and will discard the message if a continuation fails, but hang on.
Large volume of messages (many more than 1 per second).
Efficiency and throughput of message processing is critical.
Environments where a public HTTPS endpoint with a non-self-signed SSL certificate is not feasible to set up.
The subscriber client explicitly calls the pull method, which requests messages for delivery. This request is the PullRequest as shown in the image.
The Pub/Sub server responds with zero or more messages and acknowledgement IDs. A response with zero messages or with an error does not necessarily indicate that there are no messages available to receive. This response is the PullResponse as shown in the image.
The subscriber client explicitly calls the acknowledged method, using the returned acknowledgment ID to acknowledge that the message is processed and does not need be delivered again. This request is the AckRequest as shown in the image.
Multiple topics that must be processed by the same webhook.
App Engine Standard and Cloud Functions subscribers.
Environments where Google Cloud dependencies (such as credentials and the client library) are not feasible to set up.
The Pub/Sub server sends each message as an HTTPS request to the subscriber client at a pre-configured endpoint. This request is shown as a PushRequest in the image.
The endpoint acknowledges the message by returning an HTTP success status code. A non-success response indicates that the message must be re-sent. This response is shown as a PushResponse in the image.
Pub/Sub dynamically adjusts the rate of push requests based on the rate at which it receives success responses.
Create new topic
Create Subscription
Publish message to topic
