How can I diagnose why a k8s pod keeps restarting? - elasticsearch

Question

I deploy a elasticsearch to minikube with below configure file:
apiVersion: apps/v1
kind: Deployment
metadata:
name: elasticsearch
spec:
replicas: 1
selector:
matchLabels:
name: elasticsearch
template:
metadata:
labels:
name: elasticsearch
spec:
containers:
- name: elasticsearch
image: elasticsearch:7.10.1
ports:
- containerPort: 9200
- containerPort: 9300
I run the command kubectl apply -f es.yml to deploy the elasticsearch cluster.
$ kubectl get pod
NAME READY STATUS RESTARTS AGE
elasticsearch-fb9b44948-bchh2 1/1 Running 5 6m23s
The elasticsearch pod keep restarting every a few minutes. When I run kubectl describe pod command, I can see these events:
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 7m11s default-scheduler Successfully assigned default/elasticsearch-fb9b44948-bchh2 to minikube
Normal Pulled 3m18s (x5 over 7m11s) kubelet Container image "elasticsearch:7.10.1" already present on machine
Normal Created 3m18s (x5 over 7m11s) kubelet Created container elasticsearch
Normal Started 3m18s (x5 over 7m10s) kubelet Started container elasticsearch
Warning BackOff 103s (x11 over 5m56s) kubelet Back-off restarting failed container
The last event is Back-off restarting failed but I don't know why it restarts the pod. Is there any way I can check why it keeps restarting?

Answer 1

The first step (kubectl describe pod) you've already done. As a next step I suggest checking container logs: kubectl logs <pod_name>. 99% you get the reason from logs in this case (I bet on bootstrap check failure).
When neither describe pod nor logs do not have anything about the error, I get into the container with 'exec': kubectl exec -it <pod_name> -c <container_name> sh. With this you'll get a shell inside the container (of course if there IS a shell binary in it) ans so you can use it to investigate the problem manually. Note that to keep failing container alive you may need to change command and args to something like this:
command:
- /bin/sh
- -c
args:
- cat /dev/stdout
Be sure to disable probes when doing this. A container may restart if liveness probe fails, you will see that in kubectl describe pod if it happen. Since your snippet doesn't have any probes specified, you can skip this.

Answer 2

Checking logs of the pod using kubectl logs podname gives clue about what could go wrong.
ERROR: [2] bootstrap checks failed
[1]: max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]
[2]: the default discovery settings are unsuitable for production use; at least one of [discovery.seed_hosts, discovery.seed_providers, cluster.initial_master_nodes] must be configured
ERROR: Elasticsearch did not exit normally - check the logs at /usr/share/elasticsearch/logs/docker-cluster.log
Check this post for a solution