Understanding Kubernetes ConfigMap

Local Setup (Docker Desktop)

If you are using Docker Desktop and Kubernetes won’t start, common fixes include:

• Adding Chinese images mirrors.
• Using helper scripts to pull the required K8s images locally.

Verify your setup:

$ kubectl get nodes
$ kubectl cluster-info

Pods and Services

A Pod is the smallest deployable unit. Let’s start an Nginx deployment:

$ kubectl create deployment nginx --image=nginx
$ kubectl expose deployment nginx --port=80 --type=LoadBalancer
$ curl 127.0.0.1:80

ConfigMap: Decoupling Config from Code

A ConfigMap stores non-confidential data in key-value pairs. This allows you to change environment variables or configuration files without rebuilding the container image.

Creation

From literal values:

$ kubectl create configmap settings --from-literal=mode=prod

From a file:

$ kubectl create configmap app-config --from-file=config.yaml

Usage in a Pod

1. Environment Variables

env:
  - name: APP_MODE
    valueFrom:
      configMapKeyRef:
        name: settings
        key: mode

2. Mounted Volumes The ConfigMap content appears as files within the container.

volumeMounts:
  - name: config-volume
    mountPath: /etc/config
volumes:
  - name: config-volume
    configMap:
      name: app-config

Probes: Health and Readiness

A Readiness Probe tells K8s when a container is ready to start accepting traffic. If the probe fails, the Pod is removed from service endpoints.

Example: File-based Probe

readinessProbe:
  exec:
    command: ["cat", "/tmp/ready"]
  initialDelaySeconds: 5
  periodSeconds: 5

Traffic will only flow into the Pod after you manually create the file: $ kubectl exec -it [POD] -- touch /tmp/ready

Summary

ConfigMaps are essential for building portable, “write once, run anywhere” cloud-native applications. They separate the concern of how to run (Deployment) from how to configure (ConfigMap).