Guide on Asynchronous processing

By default functions are accessed synchronously via the following route:

$ curl --data "message" http://gateway/function/{function_name}

As of PR #131 asynchronous invocation is available for testing.

Logical flow for synchronous functions:

Why use Asynchronous processing?

  • Enable longer time-outs

  • Process work whenever resources are available rather than immediately

  • Consume a large batch of work within a few seconds and let it process at its own pace

How does async work?

Here is a conceptual diagram

screen shot 2017-10-26 at 15 55 19

You can also use asynchronous calls with a callback URL

screen shot 2017-10-26 at 15 55 06

Deploy the async stack

The reference implementation for asychronous processing uses NATS Streaming, but you are free to extend OpenFaaS and write your own queue-worker.


$ ./


$ kubectl -f delete ./faas.yml
$ kubectl -f apply ./faas.async.yml,nats.yml

Call a function

Functions do not need to be modified to work asynchronously, just use this alternate route:

$ http://gateway/async-function/{function_name}

If you want the function to call another function or a different endpoint when it is finished then pass the X-Callback-Url header. This is optional.

$ curl http://gateway/async-function/{function_name} --data-binary @sample.json -H "X-Callback-Url: http://gateway/function/send2slack"

Extend function timeouts

Functions have three timeouts configurable by environmental variables expressed in seconds:


  • read_timeout
  • write_timeout

Hard timeout:

  • exec_timeout

To make use of these just add them to your Dockerfile when needed as ENV variables.

Function watchdog reference