Python AnyIO + AsyncResource: Cancellation-Safe Startup/Shutdown Hooks for APIs
Build API lifecycle hooks that don’t panic when a deploy rolls through, a client disconnects, or your server sends a cancellation signal. Your startup becomes boring. Your shutdown becomes trustworthy.
The first time I hit this bug, it didn’t look like a bug.
Requests were fine. Metrics were fine. Then, during a routine redeploy, our API left behind a handful of “zombie” connections and a background consumer that sometimes kept running just long enough to double-process messages. Not always. Just enough to be spooky.
If you’ve ever tried to make startup/shutdown hooks “clean,” you already know the trap: shutdown is where cancellation goes to party.
And cancellation does not care about your finally block.
The real problem: shutdown happens inside a cancellation storm
