I've been bitten by the surprising amount of time it takes for Kubernetes to update loadbalancer target IPs in some configurations. For me, 90% of the graceful shutdown battle was just ensuring that traffic was actually being drained before pod termination.

Adding a global preStop hook with a 15 second sleep did wonders for our HTTP 503 rates. This creates time between when the loadbalancer deregistration gets kicked off, and when SIGTERM is actually passed to the application, which in turn simplifies a lot of the application-side handling.