Context

In sometimes be useful to defer an operation, possibly because the operation takes a long time to complete or because it makes it easier to maintain consistency. The client will likely need to know when the operation completes and whether it was successful.

Example

A CI server accepting requests to trigger a build.

Problem

How do we inform clients about the results of deferred operations?

Solution

First, return a response indicating that the message will be processed later, e.g. an HTTP 202. After the operation completes send a message to the client with the result. If sending the message fails, retry until it succeeds.

Notes

Polling is another solution to this problem, though has several drawbacks. Polling too frequently is wasteful, and too infrequently means updates will be delayed.

Also known as

• Webhooks

Related

• Transactional outbox – Transactionally write a description of work to be performed asynchronously