What are the reasons for Pod restart in K8S?

There are several reasons for Pod restart in K8S.

1. Manual restart: The administrator or user manually initiates the Pod restart operation.
2. Configuration changes: When the configuration file of a Pod is modified, such as changing the environment variables or resource limits of a container, K8S will automatically restart the Pod to apply these changes.
3. Node failure: If the Node running a Pod fails or becomes unavailable, K8S will automatically reschedule the Pod to another available Node and restart it.
4. Health check failed: K8S provides health check functionalities for Pods, including Liveness Probe and Readiness Probe. If either of these probes fails, K8S will automatically restart the Pod to restore its normal state.
5. Container Crash: If a container running in a Pod crashes or exits abnormally, K8S will automatically restart the Pod to attempt to recover the container’s operation.
6. System Update: When the K8S version or operating system version running on Node is updated, it may be necessary to restart the Pod to apply these updates.
7. Scaling: When the number of Pod replicas changes, such as through horizontal scaling or downsizing, K8S will automatically restart the Pod to apply the new number of replicas.

It is important to note that K8S will try to avoid unnecessary restarts and do its best to ensure high availability of applications. Therefore, when restarting a Pod, K8S will first attempt to gracefully terminate the container, wait for a period of time to ensure the container can exit normally, and then start a new container. If the process of terminating the container times out or fails, K8S will forcefully terminate the container and start a new one.