Most people are familiar with CrashLoopBackOffs, but there are actually many ways a pod can unexpectedly stop running. Here are the top four:
- OOM Kills
- CrashloopBackoff
- Init:CrashLoopBackOff
- Evictions
OOM Kills
When OOM Kills occur: A pod uses up “too much” memory. That is, more memory than the limit or more memory than is available on the node.
How OOM Kills work: The Linux Kernel kills the process, causing an OOMKill (Out of Memory Kill). No warning is given, and Kubernetes has little control over this process.
CrashloopBackoff
When CrashLoopBackOff occurs: Every time a pod crashes, Kubernetes restarts it after some time. The time between each restart is called Backoff time, and it is increased gradually. Too many restarts and it ends up in the CrashloopBackoff state.
Init:CrashLoopBackOff
What are init-containers: Init-containers are used to perform preparations before your main container runs. Your main container runs only if the Init-container exits successfully.
Pod Evictions
When evictions occur: A node runs out of resources, so Kubelet starts terminating pods to reclaim resources for essential processes. Alternatively, you can use the `Eviction API`, and manually terminate a pod.