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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?
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Enable longer time-outs
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Process work whenever resources are available rather than immediately
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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
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 -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:
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.