faas/guide/asynchronous.md

Guide on Asynchronous processing

Asynchronous function calls can be queued up using the following route:

$ curl --data "message" http://gateway:8080/async-function/{function_name}

Summary of modes for calling functions via API Gateway:

Mode	Method	URL	Body	Headers	Query string
Synchronous	POST	http://gateway:8080/function/{function_name}	Yes	Yes	Yes
Synchronous	GET	http://gateway:8080/function/{function_name}	Yes	Yes	Yes
Asynchronous	POST	http://gateway:8080/async-function/{function_name}	Yes	Yes	Yes #369
Asynchronous	GET	Not supported	-	-	-

This work was carried out under PR #131.

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

You can also use asynchronous calls with a callback URL

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.

Swarm:

$ ./deploy_extended.sh

K8s:

$ kubectl delete -f ./faas.yml
$ kubectl apply -f./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:8080/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:8080/async-function/{function_name} --data-binary @sample.json -H "X-Callback-Url: http://gateway:8080/function/send2slack"

You can also use the following site to setup a public endpoint for testing HTTP callbacks: requestb.in

Extend function timeouts

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

HTTP:

• 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