To schedule jobs only after a worker has completed the startup.

[ManelBH]

What problem would the feature you're requesting solve? Please describe.

Using HttpTriggers I have observed that when performing many requests in parallel this causes the scaler to add new instances and some of these requests get scheduled to the new instances before they complete the startup, as a result they suffer the cold start latency which is often longer than what it would take the already warm instances to process these requests in the meantime.

Describe the solution you'd like

Ideally only warm functions should be able to take jobs. If the scaler decides to add more instances they would only start taking jobs once they've warmed up to prevent unnecessarily high latencies.

[jviau]

@ManelBH you can try using warmup triggers to have a platform-level hook to initialize an instance before it is included in HTTP load balancing:
https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-warmup?tabs=isolated-process%2Cnodejs-v4&pivots=programming-language-csharp

We will add this ask to our platform backlog to track this improvement.

[lorenzadomat]

@jviau I just stumbled upon some weird behaviour related to the warmup trigger. My expectation was that other functions would only be invoked after the warmup function had finished.
However, according to our Application Insights logs, some queue-triggered functions were already invoked in parallel with the warmup trigger execution. This caused some a very long execution duration of those queue-triggered functions, because some initialisations were not finished at that point.

Could you please confirm if this is the expected behaviour, or if this might be a bug?

We are using the Node.js runtime with Azure Functions V3.

[jviau]

We are using the Node.js runtime with Azure Functions V3.

@lorenzadomat I am not sure about warmup trigger behavior in v3, as that is out of support. I recommend upgrading to v4, it might be addressed there. It also depends on what SKU you are using. Warmup trigger support/behavior varies between them, there is some support documented here. Notably, this is not supported on consumption plans.