What Is a ConfigMap in Kubernetes?

Detailed Answer

A ConfigMap is a Kubernetes API object that stores non-confidential configuration data as key-value pairs. It allows you to keep configuration separate from your container images, making applications portable across environments (dev, staging, production).

Creating a ConfigMap

From a YAML manifest:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
  namespace: default
data:
  DATABASE_HOST: "postgres.default.svc.cluster.local"
  DATABASE_PORT: "5432"
  LOG_LEVEL: "info"
  MAX_CONNECTIONS: "100"
  app.properties: |
    server.port=8080
    server.context-path=/api
    spring.profiles.active=production

From the command line:

# From literal values
kubectl create configmap app-config \
  --from-literal=DATABASE_HOST=postgres.default.svc.cluster.local \
  --from-literal=LOG_LEVEL=info

# From a file
kubectl create configmap nginx-config --from-file=nginx.conf

# From a directory
kubectl create configmap config-bundle --from-file=./config-dir/

Consuming ConfigMaps as Environment Variables

apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
    - name: app
      image: myapp:v2
      env:
        # Single key from ConfigMap
        - name: DATABASE_HOST
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: DATABASE_HOST
        # Another key
        - name: LOG_LEVEL
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: LOG_LEVEL
      resources:
        requests:
          cpu: "250m"
          memory: "256Mi"

Or inject all keys at once:

spec:
  containers:
    - name: app
      image: myapp:v2
      envFrom:
        - configMapRef:
            name: app-config

Consuming ConfigMaps as Volumes

apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
    - name: app
      image: myapp:v2
      volumeMounts:
        - name: config-volume
          mountPath: /etc/app/config
          readOnly: true
      resources:
        requests:
          cpu: "250m"
          memory: "256Mi"
  volumes:
    - name: config-volume
      configMap:
        name: app-config

Each key in the ConfigMap becomes a file in /etc/app/config/:

• /etc/app/config/DATABASE_HOST (contains "postgres.default.svc.cluster.local")
• /etc/app/config/LOG_LEVEL (contains "info")
• /etc/app/config/app.properties (contains the multiline properties)

Selecting Specific Keys

Mount only certain keys as files:

volumes:
  - name: config-volume
    configMap:
      name: app-config
      items:
        - key: app.properties
          path: application.properties

This creates a single file at /etc/app/config/application.properties.

Update Behavior

| Consumption Method | Auto-Updates? | Notes | |---|---|---| | Environment variable | No | Pod restart required | | Volume mount | Yes | Updated within kubelet sync period (default ~60s) | | SubPath volume mount | No | SubPath breaks the symlink-based update mechanism |

Limitations

• Size limit: ConfigMaps cannot exceed 1 MiB
• Namespace-scoped: Cannot be shared across namespaces
• No encryption: Data is stored in plaintext in etcd — do not store secrets
• No templating: Values are static strings — no variable interpolation