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Signed-off-by: eiji.ienaga <eiji.ienaga@gmail.com>
82 lines
2.6 KiB
Markdown
82 lines
2.6 KiB
Markdown
# Chaining OpenFaaS functions
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We will discuss client-side piping, server-side piping and the "function director" pattern.
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## Client-side piping
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The easiest way to chain functions is to do it on the client-side via your application code or a `curl`.
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Here is an example:
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We pipe a string or file into the markdown function, then pipe it into a Slack function
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```
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$ curl -d "# test" localhost:8080/function/markdown | \
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curl localhost:8080/function/slack --data-binary -
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```
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You could also do this via code, or through the `faas-cli`:
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```
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$ echo "test" | faas-cli invoke markdown | \
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faas-cli invoke slack
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```
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## Server-side access via gateway
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On the server side you can access any other function by calling it on the gateway over HTTP.
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### Function A calls B
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Let's say we have two functions:
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* geolocatecity - gives a city name for a lat/lon combo in JSON format
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* findiss - finds the location of the International Space Station then pretty-prints the city name by using the `geolocatecity` function
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findiss Python 2.7 handler:
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```
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import requests
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def get_space_station_location():
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return {"lat": 0.51112, "lon": -0.1234}
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def handler(st):
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location = get_space_station_location()
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r = requests.post("http://gateway:8080/function/geolocatecity", location)
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print("The ISS is over the following city: " + r.content)
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```
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### Function Director pattern
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In the Function Director pattern - we create a "wrapper function" which can then either pipes the result of function call A into function call B or compose the results of A and B before returning a result. This approach saves on bandwidth and latency vs. client-side piping and means you can version both your connector and the functions involved.
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Take our previous example:
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```
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$ curl -d "# test" localhost:8080/function/markdown | \
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curl localhost:8080/function/slack --data-binary -
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```
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markdown2slack Python 2.7 handler:
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```
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import requests
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def handler(req):
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markdown = requests.post("http://gateway:8080/function/markdown", req)
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slack_result = requests.post("http://gateway:8080/function/slack", markdown.content)
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print("Slack result: " + str(slack_result.status_code))
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```
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Practical example:
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GitHub sends a "star" event to tweetfanclub function, tweetfanclub uses get-avatar to download the user's profile picture - stores that in an S3 bucket, then invokes tweetstargazer which tweets the image. A polaroid effect is added by a "polaroid" function.
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This example uses a mix of regular binaries such as ImageMagick and Python handlers generated with the FaaS-CLI.
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* [GitHub to Twitter Fanclub](https://github.com/alexellis/faas-twitter-fanclub/blob/master/README.md)
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