Azure Functions
An Azure service that provides an event-driven serverless compute platform.
Service Bus Azure Function repeatedly fails with timeout when trying to start a Durable Functions Orchestration
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David Faivre - PCS
1
Reputation point
Service Bus Azure Function repeatedly fails with timeout when trying to start a Durable Functions Orchestration
We have a service bus function that listens for a service bus message, and starts a durable function orchestration. It will, maybe a couple times a die, start repeatedly failing with timeout RpcExceptions, assumedly when calling the underlying functions runtime. From the Azure troubleshooting, it looks like there are "Port 4001 in use errors" that would also point to the Azure Functions runtime failing. The only way to fix it is to restart the entire Functions App.
Time period: 2025-10-23 – 8:15 AM - 3:00PM US/Chicago/Central Time
In the logging below - we restarted the Functions App at ~8:50AM and ~3:00PM. The auto scale instance spikes are, I assume, the Service Bus functions starting a bunch of Durable Orchestrations.
It seems like we scale down to one auto scale instance, that instance's functions runtime dies and can't restart, then our functions become stuck until we restart. When multiple instances are running, it seems more robust, since as long as there is at least one instance with the functions runtime healthy, it can push through Orchestration starts.
NOTE - I can provide some error log screen shots/etc, but it isn't letting me include them.
Azure Functions
{count} votes
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David Faivre - PCS 1 Reputation point
2025-10-24T14:31:02.2533333+00:00 Azure Errors Report Time in UTC
Timeout Error History Time in Central
Function Auto Scale Instance Count
Time in Central Time
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David Faivre - PCS 1 Reputation point
2025-10-24T14:31:37.5366667+00:00 Possibly related github issue: https://github.com/Azure/azure-functions-durable-extension/issues/2970
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Pravallika KV 165 Reputation points Microsoft External Staff Moderator2025-10-24T15:15:32.27+00:00 Thanks for reaching out to Microsoft Q&A,
- The issue happens because the Durable Functions runtime sometimes crashes or locks up on port 4001 after scaling down.
- When that happens, the Service Bus trigger can’t start new orchestrations and times out.
- Upgrading the Durable Functions extension to 2.11.2 or later versions usually fixes this problem.
- Try keeping the Function App “Always On” or add a small timer-triggered keep-alive.
- Separate your Service Bus trigger and Durable orchestrator into different Function Apps for reliability.
- Use the Azure Storage backend and add simple retry logic when starting orchestrations which makes the system more stable.
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David Faivre - PCS 1 Reputation point
2025-10-24T15:26:13.6033333+00:00 Thanks @Pravallika KV -- I don't see anywhere in our Functions App that has the "Durable Functions extension" version, and it seems all our NuGets are up to date.
- I'm not sure this is possible, since the Service Bus function needs the Azure Durable Functions runtime/sidecar? I've never seen examples where we are able to separate them?
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Pashikanti Kumar 1,080 Reputation points Microsoft External Staff Moderator2025-10-24T19:45:16.0966667+00:00 Confirm Durable Functions Extension Version
- Verify the version of the Microsoft.Azure.WebJobs.Extensions.DurableTask NuGet package in your project.
- If the version is below 2.11.2, upgrade it using the following command:
dotnet add package Microsoft.Azure.WebJobs.Extensions.DurableTask --version 2.11.2- Redeploy the Function App after upgrading.
If runtime crashes persist, consider separating the Service Bus trigger and Durable orchestrator into different Function Apps for better reliability.
- Use the Durable Functions HTTP API to start orchestrations from the Service Bus trigger.
- Example flow:
Function App 1: Service Bus trigger processes the message and sends an HTTP POST request to the Durable Functions orchestrator.
Function App 2: Durable Functions orchestrator handles the orchestration logic.
Optimize Service Bus trigger settings in host.json.
If runtime issues persist, consider separating Service Bus trigger and Durable orchestrator into different Function Apps.
Use Application Insights to monitor and diagnose runtime health.
Kindly let us know if the above helps or you need further assistance on this issue.
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Thanks
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