Kubernetes ConfigMaps

What Is a ConfigMap?

A ConfigMap stores non-sensitive configuration data so applications can read settings at runtime instead of hardcoding them into images.

Create a ConfigMap from Literals

kubectl create configmap app-config   --from-literal=APP_ENV=dev   --from-literal=LOG_LEVEL=info

Create a ConfigMap from a File

kubectl create configmap nginx-config --from-file=nginx.conf

Create a ConfigMap from YAML

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  APP_ENV: dev
  LOG_LEVEL: info

Use as Environment Variables with envFrom

apiVersion: v1
kind: Pod
metadata:
  name: env-config-demo
spec:
  containers:
    - name: app
      image: busybox:1.36
      command: ['sh', '-c', 'env | grep APP_ && sleep 3600']
      envFrom:
        - configMapRef:
            name: app-config

Use a Single Key with valueFrom

apiVersion: v1
kind: Pod
metadata:
  name: single-key-demo
spec:
  containers:
    - name: app
      image: busybox:1.36
      command: ['sh', '-c', 'echo $LOG_LEVEL && sleep 3600']
      env:
        - name: LOG_LEVEL
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: LOG_LEVEL

Use as Mounted Files

apiVersion: v1
kind: Pod
metadata:
  name: file-config-demo
spec:
  volumes:
    - name: config-volume
      configMap:
        name: app-config
  containers:
    - name: app
      image: busybox:1.36
      command: ['sh', '-c', 'ls /config && sleep 3600']
      volumeMounts:
        - name: config-volume
          mountPath: /config

Inspect ConfigMaps

kubectl get cm
kubectl describe cm app-config

Why Two Consumption Patterns Exist

Environment variables are simple for app settings. Mounted files are better when the app expects actual config files.