Azure Function Timer triggers fail to execute when the server is under heavy load

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I've discovered that Azure Function Timer triggers fail to execute when the server is under heavy load with other Azure Functions. I suspect this is by design, or simply a failed consideration. I need to designed a solution that enables triggering high priority Azure Functions regardless of current trigger requests and server load.

What is the best approach to prioritize mission critical Azure Functions over lower priority executions?

You can see from the example that a timer trigger scheduled every 5 minutes fails to execute when the server is under heavy load.

Server is on an S2 Plan. Application is C# running Azure Function v1.0.29. Cannot update to v3.x because this is not a .NET Core project.

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c#azureazure-functions
Can you provide any piece of trigger code and host.json? - J.Wincewicz

1 Answers

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From the official wiki:

If your function execution takes longer than the timer interval, another execution won't be triggered until after the current invocation completes. The next execution is scheduled after the current execution completes.

https://github.com/Azure/azure-webjobs-sdk-extensions/wiki/TimerTrigger#scheduling

You can try using Durable Functions (Eternal orchestration) and pass the process to child activities:

https://docs.microsoft.com/en-au/azure/azure-functions/durable/durable-functions-eternal-orchestrations?tabs=csharp