[Azure Functions / Python] Chain functions with Queue Storage binding

Introduction

This article aims to chain Azure Functions using Queue Storage bindings among Azure Functions.

The outline is as follows,

• Azure Functions launched by HTTP request enqueues messages to Queue Storage
• Launch another Azure Functions triggered by enqueue to Queue

It looks like this in the figure.

1. User etc. hit curl
2. Azure Function of ② starts
3. Queue Storage has messages enqueue
4. Azure Functions of ③ starts with enqueue as trigger

Premise

• You can create and deploy Azure Functions using VS Code etc.
• Azure Functions of ② and ③ are linked to the same region / Storage Account

Preparation / implementation

Preparation: ① Queue Storage

Create a Queue called piyo in Queue Storage from the" + Queue "button.

Implementation: ② Azure Functions

Create Azure Functions for HTTP Trigger from VS Code and modify the automatically generated code. Add the bottom 5 items, " type "," direction "," name "," queueName "," connection ". (If it is VSCode, you can also add it with add binding.)

function.json

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "authLevel": "anonymous",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    },
    {
      "type": "queue",
      "direction": "out",
      "name": "fuga1",
      "queueName": "piyo",
      "connection": "AzureWebJobsStorage"
    }
  ]
}

The additional items are briefly explained below. A setting that fits easily is name. This name is the argument name you receive in your python program. (At first, I didn't understand this, and the output of the function execution log was slow, so it took time to identify the cause of the error ...)

Next is the Python code body. Now, put fuga1 in the argument of the main function. That is, specify the same name as function.json. ** Caution If you put a symbol such as _ in name, it will not work. ** **

__init__.py

import logging
import azure.functions as func


def main(req: func.HttpRequest, fuga1: func.Out[str]) -> func.HttpResponse:
    logging.info('Python HTTP trigger function processed a request.')

    #Get parameters
    name = req.params.get('name')
    #Put in queue
    fuga1.set(name)
    
    #Return value (It is a little longer in the case of automatic generation, but it is omitted because it is not relevant here)
    return func.HttpResponse("\n".join(return_list))

Implementation: ③ Azure Functions

As in (2), the Queue Trigger function is automatically generated from VS Code this time. This time only the input binding. For queueName, specify piyo of Queue Storage. name is fuga2. This name can be uniquely determined for each ʻAzure Functions`.

function.json

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "fuga2",
      "type": "queueTrigger",
      "direction": "in",
      "queueName": "piyo",
      "connection": "AzureWebJobsStorage"
    }
  ]
}

Next is the Python code body. Modify only the argument of the main function to the variable name fuga2 specified in function.json.

__init__.py

import logging
import azure.functions as func


def main(fuga2: func.QueueMessage) -> None:
    logging.info('Python queue trigger function processed a queue item: %s',
                 fuga2.get_body().decode('utf-8'))

Execution example

If you hit it from your local curl, you can see from the log that it's working.

First of all, Azure Functions of ② is started by HTTP request,

③ Azure Functions is started with Queue as a trigger.

You can see that Azure Functions is running 2 seconds after the message is entered in the Queue. (Close your eyes on the function name ...)

in conclusion

I found that it can be chained with Queue Trigger of Azure Functions. When creating a service that actually works, it seems that Azure Functions can be chained nicely by generating the name of Queue well and using multiple out bindings.

reference

• [Azure Functions] Call another Function from Function with Queue Storage bind
• [Official] Azure Queue storage output bindings in Azure Functions