What happens to existing requests when auto-heal restarts an app?

Question

For auto-heal triggers like memory or request count, when azure decides to auto-heal an app service instance, what happens to the requests that are in-progress?

Is the service instance taken out of rotation and allowed to drain in-progress requests before the app service instance is restarted?

It would be bad if the app service instance did a hard reset and dropped all the existing requests.

Answer 1

Auto-Healing does not change the instance of the app. whenever the configured condition criteria is met, Auto-healing recycles the worker process serving the requests on the same instance.

Whenever the process is recycled via Auto-healing, a new w3wp.exe will spun up and will start picking up new requests that are currently in the HTTP.SYS queue. The in-flight (requests that are already picked up by the old worker process) are allowed to finish gracefully and then the process is allowed to exit. The old process is given 60 (or 90 seconds, need to check) to exit and if within that time the process has not finished serving all the in-flight requests, the process will be terminated.