How to use callbacks for long-running Azure Functions in a DevOps pipeline? - azure

Question

I have an Azure DevOps release pipeline that deploys a Python Azure function and then invokes it. The Python function does some heavy lifting, so it takes a few minutes to execute.
There are two options for the completion event for the Invoke Azure Function task: Api Response and Callback.0
The maximum response time when using Api Response is 20 seconds, so I need to use Callback. OK, fine. Using this documentation, I implemented an Azure function that returns an HTTPResponse immediately, and then posts completion data to the specified endpoint. Here's the complete code for my Azure function:
import logging
import time
import threading
import azure.functions as func
def main(req: func.HttpRequest) -> func.HttpResponse:
t = threading.Thread(target=do_work, args=(req,))
t.start()
return func.HttpResponse("Succeeded", status_code=200)
def do_work(req: func.HttpRequest):
logging.info ("Starting asynchronous worker task")
#time.sleep(21)
try:
planUrl = req.headers["PlanUrl"]
projectId = req.headers["ProjectId"]
hubName = req.headers["HubName"]
planId = req.headers["PlanId"]
taskInstanceId = req.headers["TaskInstanceId"]
jobId = req.headers["JobId"]
endpoint = f"{planUrl}/{projectId}/_apis/distributedtask/hubs/{hubName}/plans/{planId}/events?api-version=2.0-preview.1"
body = {
"name": "TaskCompleted",
"taskId": taskInstanceId,
"jobId": jobId,
"result": "succeeded"
}
logging.info(endpoint)
logging.info(body)
requests.post(endpoint, data=body)
except:
pass
finally:
logging.info ("Completed asynchronous worker task")
Now, the Invoke Azure Function task doesn't time out, but it doesn't complete either. It just looks like it's waiting for something else to happen:
Not sure what I'm supposed to do here. I'm also following this thread on GitHub, but it's not leading to a resolution.

Answer 1

Unless you are using Durable functions (which shouldn't be necessary here), background jobs as part of a function execution like this is not supported with Azure Functions.
Once a response is returned by a function, that channel is closed in a way that any background operations would not work as expected (exception- Durable Functions).
If you need something to work asynchronously like this and you are ok not waiting for a response, the recommended approach would be to use multiple functions.
In this case, your HttpTrigger could drop a message in the queue (or any other messaging service) and return a response immediately. Then, you'd have a queue trigger (or other event based trigger) to pick up events from the queue (or any such messaging service) and do your heavy lifting and once completed, could post to that endpoint in your example.
If you want to implement this with just one function, then from your devops pipeline, you could directly drop a message to a messaging service and have your function trigger off of that.
Hope this helps!

Answer 2

I can't find it explicitly documented anywhere, but it appears you need to add an authorization header (at least when running locally)
Debugging my (very similar C#) function, the callback response gives me a 204 status code with an empty body when I include the header, and a 203 response with an Azure DevOps sign in page in the body when I do not.
The bearer token is passed in the same way as the other system variables, as AuthToken so you need to add the Authorization header with a value of "Bearer " + req.headers["AuthToken"]