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78 lines
3.1 KiB
Markdown
78 lines
3.1 KiB
Markdown
# Guide on Asynchronous processing
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Asynchronous function calls can be queued up using the following route:
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```
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$ curl --data "message" http://gateway:8080/async-function/{function_name}
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```
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Summary of modes for calling functions via API Gateway:
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| Mode | Method | URL | Body | Headers | Query string
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| -------------|--------|------------------------------------------------|------|--------- |------------------- |
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| Synchronous | POST | http://gateway:8080/function/{function_name} | Yes | Yes | Yes |
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| Synchronous | GET | http://gateway:8080/function/{function_name} | Yes | Yes | Yes |
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| Asynchronous | POST | http://gateway:8080/async-function/{function_name} | Yes | Yes | Yes [#369](https://github.com/openfaas/faas/issues/369) |
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| Asynchronous | GET | Not supported | - | - | - |
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> Note: This work was originally carried out under [PR #131](https://github.com/openfaas/faas/pull/131).
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*Logical flow for synchronous functions:*
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## 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
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## How does async work?
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Here is a conceptual diagram
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<img width="1440" alt="screen shot 2017-10-26 at 15 55 19" src="https://user-images.githubusercontent.com/6358735/32060206-047eb75c-ba66-11e7-94d3-1343ea1811db.png">
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You can also use asynchronous calls with a callback URL
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<img width="1440" alt="screen shot 2017-10-26 at 15 55 06" src="https://user-images.githubusercontent.com/6358735/32060205-04545692-ba66-11e7-9e6d-b800a07b9bf5.png">
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The reference implementation for asychronous processing uses NATS Streaming, but you are free to extend OpenFaaS and write your own [queue-worker](https://github.com/open-faas/nats-queue-worker).
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> The asynchronous stack is now built-in by default. Previously it was an optional configuration.
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## Call a function
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Functions do not need to be modified to work asynchronously, just use this alternate route:
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```
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http://gateway:8080/async-function/{function_name}
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```
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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.
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```
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$ curl http://gateway:8080/async-function/{function_name} --data-binary @sample.json -H "X-Callback-Url: http://gateway:8080/function/send2slack"
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```
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You can also use the following site to setup a public endpoint for testing HTTP callbacks: [requestb.in](https://requestb.in)
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## Extend function timeouts
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Functions have three timeouts configurable by environmental variables expressed in seconds:
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HTTP:
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* read_timeout
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* write_timeout
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Hard timeout:
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* exec_timeout
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To make use of these just add them to your Dockerfile when needed as ENV variables.
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> [Function watchdog reference](https://github.com/openfaas/faas/tree/master/watchdog)
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