Logging

Logging is one option to understand what is going on inside your applications and the cluster at large. Basic logging in Kubernetes makes the output a container produces available through the kubectl tool. More advanced setups consider logs across nodes and store them in a central place, either within the cluster or via a dedicated (cloud-based) service.

Let’s create a pod called logme that runs a container writing to stdout and stderr:

$ kubectl apply -f https://github.com/openshift-evangelists/kbe/raw/main/specs/logging/pod.yaml

To view the five most recent log lines of the gen container in the logme pod, execute:

$ kubectl logs --tail=5 logme -c gen

Streaming functionality, similar to running tail -f, is available as well:

$ kubectl logs -f --since=10s logme -c gen

Note that if you didn’t specify --since=10s in the above command, you would have gotten all of the log lines from the start of the container.

You can also view logs of pods that have already completed their lifecycle. To demonstrate this, create a pod called oneshot that counts down from 9 to 1 and then exits:

$ kubectl apply -f https://github.com/openshift-evangelists/kbe/raw/main/specs/logging/oneshotpod.yaml

By using the -p option, you can print the logs for previous instances of the container in a pod:

$ kubectl logs -p oneshot -c gen

You can remove the created pods with:

$ kubectl delete pod/logme pod/oneshot

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