kubectl logs

Learn to view Pod logs with kubectl logs.

kubectl logs

The first step of troubleshooting is the logs. kubectl logs shows a container's stdout/stderr output; you can select the pod by name or through its owner (deploy/web):

kubectl logs web-7c5b9f6d8-abcde
kubectl logs deploy/web                 # one pod of the deployment
kubectl logs -f deploy/web --since=10m  # live, last 10 minutes
kubectl logs api-xyz -c log-gonderici   # multi-container pod
kubectl logs api-xyz --previous         # the previous, crashed container

When are logs lost?

The kubelet keeps logs on the node and rotates them. When a pod is deleted or moved to another node, its logs go too. That is why in production logs are sent to a central system (in the advanced section: Fluentd, Elasticsearch, Loki). For short-lived problems, --previous still gives the last log of the previous container.

kubectl logs -l app=api --all-containers --prefix --tail=20
kubectl logs api-xyz --timestamps | grep -i error

Exercise Scan the logs

Write three commands: show the last 20 lines of all pods labelled app=api with prefixes; show the previous container log of api-5d8f7c9b4-qrstu; follow the last 10 minutes of deploy/web live.

Show example solution

kubectl logs -l app=api --tail=20 --prefix
kubectl logs api-5d8f7c9b4-qrstu --previous
kubectl logs -f deploy/web --since=10m

Test yourself

What does kubectl logs deploy/web show when there are several replicas?
- It errors
- The log of only one of the pods
- The logs of all pods
- The deployment events
Show answer

The log of only one of the pods — For all replicas, -l app=web --prefix is used.

Get the logs of all containers.

kubectl logs api-xyz ____

Show answer

kubectl logs api-xyz --all-containers

Match.

-f

Follow live
-c

Pick a container
--previous

Crashed one's log
--prefix

Pod name prefix

Next lesson: kubectl exec

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