PreStop
What is “PreStop”?
“PreStop” is a kind of container lifecycle hooks. Kubernetes provides Containers with lifecycle hooks. The hooks enable Containers to be aware of events in their management lifecycle and run code implemented in a handler when the corresponding lifecycle hook is executed. “PreStop” is called immediately before a container is terminated due to an API request or management event such as liveness probe failure, preemption, resource contention and others.
Why “PreStop” is necessary?
A new connection may be established during executing a Pod Rolling Upgrade even though an old version of the Pod is being deleted. It is due to Kubernetes specifications. To avoid this, it is necessary to wait for a time when a new connection may be established with the sleep command, and execute a graceful shutdown when a new connection can no longer be established.