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Troubleshooting Azure function app: Did not find any initialized language workers

Azure function app random response 500 Internal error to client. log indicate Azure function: Did not find any initialized language workers.

Symptom

We deployed a very simple Azure function with nodejs runtime, on an Linux container. However after deployment, the service is not stable stable, it goes up and down, server random response 500 Internal error to client.

From Azure’s log, it indicate Azure function: Did not find any initialized language workers:

2020-02-13 19:21:44.682 Error Executed 'Functions.foo' (Failed, Id=4ff2c8f3-4504-4f6d-bf9c-886409c5f517)
2020-02-13 19:21:44.689 Error Did not find any initialized language workers

Azure function app error log

Tried to search this error online and lot of recommendation is setting environment var WEBSITE_NODE_DEFAULT_VERSION for nodejs, We tried to set WEBSITE_NODE_DEFAULT_VERSION to ~10 to make sure it can have a valid nodejs runtime. However this does not solve issue.

Mitigation

Since un-know the root cause of problem, we end up re-create function app in another region, with a windows machine, a new app service plan. It solve the issue.

We previous create function app in an exist app service plan, and there is issue on create function app in exist app plan. not sure related or not:

this resource group already contains regular (i.e. non-Dynamic or Premium) Web Apps in the same region that you’re trying to create the Function App. This can even occur if you are creating a Azure Functions Premium Plan in a resource group that has an App Service Premium Plan of the same OS.

Reference