How do ConfigMaps work and how do updates propagate?

ConfigMaps decouple configuration from images. You can create them from literals, files or directories, then reference keys individually or mount the whole object as a volume. This lets the same image run in different environments with different settings.

• Environment variables are read at container start and do not update in place
• Mounted ConfigMap volumes are updated by kubelet, usually within a minute or so
• Applications must watch the files to pick up changes
• subPath mounts do not receive updates
• immutable: true prevents changes and reduces API server load

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  LOG_LEVEL: info
  feature-flags.json: |
    {"newCheckout": true}
---
apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
    - name: app
      image: registry.example.com/app:3.0.1
      envFrom:
        - configMapRef:
            name: app-config
      volumeMounts:
        - name: config
          mountPath: /etc/app
  volumes:
    - name: config
      configMap:
        name: app-config

For most stateless services, changing configuration means rolling the Deployment so pods restart with the new values. If you need live reload, mount files and implement a watcher. Never assume an environment variable changed because the ConfigMap changed.