Add note about Kubernetes termination grace period

Closes gh-26469

spring-boot-project/spring-boot-docs/src/docs/asciidoc/deployment.adoc

@@ -192,6 +192,10 @@ spec:
 
 Once the pre-stop hook has completed, SIGTERM will be sent to the container and <<spring-boot-features#boot-features-graceful-shutdown,graceful shutdown>> will begin, allowing any remaining in-flight requests to complete.
 
+NOTE: When Kubernetes sends a SIGTERM signal to the pod, it waits for a specified time called the termination grace period (the default for which is 30 seconds).
+If the containers are still running after the grace period, they are sent the SIGKILL signal and forcibly removed.
+If the pod takes longer than 30 seconds to shut down, which could be because you've increased spring.lifecycle.timeout-per-shutdown-phase, make sure to increase the termination grace period by setting the `terminationGracePeriodSeconds` option in the Pod YAML.
+
 
 
 [[cloud-deployment-heroku]]