Poststart Hook Using only process signals for managing lifecycles is somewhat limited. That is why there are additional lifecycle hooks such as  postStart  and  preStop  provided by Kubernetes. A Pod manifest containing a  postStart  hook looks like the one in Example 5-1. The  postStart  command is executed after a container is created, asynchronously with the primary container’s process. Even if many of the application initialization and warm-up logic can be implemented as part of the container startup steps,  post Start  still covers some use cases. The  postStart  action is a blocking call, and the container status remains  Waiting  until the  postStart  handler completes, which in turn keeps the Pod status in the  Pending  state. This nature of  postStart  can be used to delay the startup state of the container while giving time to the main container process to initialize. Another use of  postStart  is to prevent a container from starting when the Pod does not fulfill certain preconditions. For example, when the  postStart  hook indicates an error by returning a nonzero exit code, the main container process gets killed by Kubernetes. Solution  |  43 apiVersion : v1 kind : Pod metadata : name : post-start-hook spec : containers : -  image : k8spatterns/random-generator:1.0 name : random-generator lifecycle : postStart : exec : command : - sh - -c - sleep 30 && echo "Wake up!" > /tmp/postStart_done Example 5-1. A container with poststart hook The  postStart  command waits here 30 seconds.  sleep  is just a simulation for any lengthy startup code that might run here. Also, it uses a trigger file here to sync with the main application, which starts in parallel.