Gotcha: Kubernetes ConfigMap updates don't trigger pod restart

Updating a ConfigMap doesn't automatically restart pods that use it, leaving them with stale configuration.

ConfigMap update propagation:

# Problem: Pod uses ConfigMap as env vars
# Updating ConfigMap does NOT restart the pod!

# Solution 1: Add ConfigMap hash as annotation
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  template:
    metadata:
      annotations:
        # Change this when ConfigMap changes -> triggers rollout
        configmap-hash: "abc123"  # Update manually or via CI
    spec:
      containers:
        - name: app
          envFrom:
            - configMapRef:
                name: myapp-config

# Solution 2: Use kubectl rollout restart
kubectl rollout restart deployment/myapp
# Triggers a rolling restart of all pods

# Solution 3: Volume-mounted ConfigMaps DO auto-update!
# (But only for volume mounts, NOT env vars)
spec:
  containers:
    - name: app
      volumeMounts:
        - name: config
          mountPath: /etc/config
  volumes:
    - name: config
      configMap:
        name: myapp-config
# Files in /etc/config update within ~60s
# But your app must watch for file changes!

# Solution 4: Immutable ConfigMaps (Kubernetes 1.21+)
apiVersion: v1
kind: ConfigMap
metadata:
  name: myapp-config-v2  # New name for each version
immutable: true
data:
  APP_MODE: production
# Update deployment to reference new ConfigMap name
# Old ConfigMap can be garbage collected

# Solution 5: Use Reloader (open source controller)
# https://github.com/stakater/Reloader
# Automatically restarts pods when ConfigMap/Secret changes
metadata:
  annotations:
    reloader.stakater.com/auto: "true"

Kubernetes doesn't restart pods when ConfigMaps change because it could cause unexpected downtime. The tradeoff is that pods can run with stale config until explicitly restarted.

Kubernetes configuration management