Handling SIGTERM and SIGKILL on Spring Boot web applications

This post was reproduced here as well

When debugging one system recently, I found out that every time that a deploy, downscale, container rotation or k8s updates happened I had a lot of connection errors in the ingress car.

In common on those situations, is that k8s sends a SIGTERM, then have a grace period for the application to handle it gracefully, and after N seconds, it sends a SIGKILL, and that is the end.

At first, being a little bit reluctant that the issue was with Spring Boot or the web server that I run with (Tomcat), I tried to check every possible misbehave from the load balancer, no success.

One example on how this works, but mainly from AWS ECS:

Then, after some digging into the server properties in Spring Boot, we found out that the common behaviour for the web server is to shutdown immediately after receiving a SIGTERM, not waiting for any persistentkeep-alive connections to be properly finished and closed.

And how did I fix this?

So, in order to fix that, you must add a line to your application.properties or application.yml file like this:

    server.shutdown=graceful

OR

server:
    shutdown: graceful

Passing graceful to the server shutdown property allows the web server to support graceful shutdown, allowing active requests time to complete and close any persistent keep-alive connections towards your service.

Oh, and if in any case you ended up here but want to know more how Quarkus handles this, i suggest you to take a look here, because it explains in an easy way how to implement this on Quarkus.