Challenge, Easy,  on  Kubernetes

Resolve ContainerCreating Issue Caused by Missing ConfigMap

Omkar Shelke
by  Omkar Shelke

Scenario

A Deployment named web-hydrogen is running in the hydrogen namespace with 2 replicas, but both Pods are stuck in ContainerCreating state and never reach Running. Users trying to reach the application get nothing — the NodePort doesn't respond.

The Deployment mounts a ConfigMap as a volume to serve a static HTML page, but that ConfigMap was never created. The source file for the page is already on dev-machine:

/home/laborant/web-hydrogen.html

Task

  1. Create a ConfigMap named configmap-web-hydrogen-html in the hydrogen namespace from /home/laborant/web-hydrogen.html, storing its content under the key index.html
  2. Make sure the existing Pods actually pick up the fix — check whether they recover automatically or need to be restarted
  3. Confirm the application responds successfully on NodePort 30099
# Test application
curl http://cplane-01:30099
Hint 1 — Diagnose the Stuck Pods

Check the Pod status and look at the events to find the exact failure reason:

kubectl get pods -n hydrogen
kubectl describe pod -n hydrogen -l app=web-hydrogen

Look in the Events section near the bottom of the describe output, and check the Volumes section to see what resource the Pod is trying to mount.

Documentation

Hint 2 — Create the ConfigMap from a File with a Custom Key

Use kubectl create -h and kubectl create configmap -h to discover how to create a ConfigMap from a file while setting a custom key name — the key does not have to match the source filename.

The file /home/laborant/web-hydrogen.html needs to become a ConfigMap named configmap-web-hydrogen-html in the hydrogen namespace, with its content stored under the key index.html.

Documentation

Hint 3 — Existing Pods May Not Recover on Their Own

Creating the ConfigMap does not always make the already-stuck Pods recover immediately — kubelet retries failed mounts on a backoff schedule, which can take a while. If the Pods don't transition to Running shortly after the ConfigMap is created, force a fresh rollout:

kubectl rollout restart deployment web-hydrogen -n hydrogen

Once running, verify the Service has endpoints and the app responds:

kubectl get endpoints web-hydrogen-service -n hydrogen
curl http://cplane-01:30099

Documentation

Test Cases

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