Introduction to ConfigMaps

Hardcoding configuration parameters into container images is an anti-pattern: it forces you to rebuild images when changing trivial settings (like API endpoints or feature flags) across development, staging, and production.

A ConfigMap allows you to externalize configuration values, storing them as key-value pairs directly in the cluster registry (etcd). ConfigMaps have a maximum object size limit of 1MB and are designed for non-sensitive data.

ConfigMap Creation Patterns

You can create ConfigMaps imperatively using the CLI or declaratively using YAML manifests:

# Create ConfigMap from literal values
kubectl create configmap app-env --from-literal=API_ENDPOINT=https://api.prod.com
Create ConfigMap from a local file
kubectl create configmap app-settings --from-file=config.properties

Mounting ConfigMaps into Workloads

Kubernetes supports two primary methods for injecting ConfigMaps into containers:

• Environment Variables: Maps ConfigMap keys directly to environment variables inside the container, making them accessible to application startup logic.
• Volume Mounts: Mounts ConfigMap keys as files inside a directory. Each key becomes a filename, and its value becomes the file content.

YAML Manifest Examples

Here is a ConfigMap configuration and a Pod that mounts it as both environment variables and files:

# 1. ConfigMap Manifest
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  APP_COLOR: "blue"
  properties_file: |
    database.timeout=30
    database.pool.size=10
2. Pod Manifest Mounting ConfigMap
apiVersion: v1
kind: Pod
metadata:
  name: web-app-pod
spec:
  containers:
  - name: app-container
    image: nginx:alpine
    # Method A: Inject as Environment Variable
    env:
    - name: THEME_COLOR
      valueFrom:
        configMapKeyRef:
          name: app-config
          key: APP_COLOR
    # Method B: Mount as Files in a Volume
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: app-config