ConfigMap

A ConfigMap in Kubernetes is an API object used to store non-confidential configuration data in key-value pairs, so you can separate configuration from application code.

It allows you to dynamically configure your applications without rebuilding container images.

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⚙️ Definition

A ConfigMap provides a way to inject configuration data into Pods — such as environment variables, command-line arguments, or configuration files.

ConfigMaps are ideal for settings, not secrets. (Sensitive data → use a Secret instead.)

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🧩 Why Use a ConfigMap

• Keeps your app code independent of environment-specific settings.
• Allows configuration changes without modifying or redeploying container images.
• Makes your system portable across environments (dev, test, prod).

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🧾 Example 1: Simple Key-Value ConfigMap

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  APP_MODE: "production"
  APP_PORT: "8080"
  LOG_LEVEL: "info"

You can create this from a file or literal values using kubectl:

kubectl create configmap app-config --from-literal=APP_MODE=production --from-literal=APP_PORT=8080

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🧾 Example 2: File-Based ConfigMap

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config-files
data:
  config.json: |
    {
      "debug": false,
      "maxConnections": 100
    }
  app.properties: |
    message=Welcome to Kubernetes

This allows you to mount configuration files directly inside your Pods.

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🧰 Using a ConfigMap in a Pod

1. As Environment Variables

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
spec:
  containers:
    - name: myapp
      image: nginx
      envFrom:
        - configMapRef:
            name: app-config

Result:
Inside the container:

$ echo $APP_MODE
production

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2. As Individual Environment Variables

env:
  - name: LOG_LEVEL
    valueFrom:
      configMapKeyRef:
        name: app-config
        key: LOG_LEVEL

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3. As Mounted Files

apiVersion: v1
kind: Pod
metadata:
  name: configmap-volume-pod
spec:
  containers:
    - name: myapp
      image: busybox
      command: ["cat", "/etc/config/app.properties"]
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        name: app-config-files

Result:
Files from the ConfigMap (config.json, app.properties) appear under /etc/config.

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🔄 Updating a ConfigMap

• If you update a ConfigMap, Pods won’t automatically reload the new values.
• You need to restart the Pods (or use a sidecar/reloader pattern) to apply the new config.

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🧠 Best Practices

Practice	Description
Keep secrets out	Don’t store passwords or tokens — use Secrets.
Use labels	Helps organize ConfigMaps for different apps/environments.
Small ConfigMaps	Avoid large files or binary data.
Version your ConfigMaps	Use naming conventions (e.g., app-config-v2).
Automate reload	Use tools like Reloader, Stakater, or custom scripts.

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📊 ConfigMap vs Secret

Feature	ConfigMap	Secret
Purpose	Non-sensitive config data	Sensitive data (passwords, tokens)
Storage	Plain text	Base64-encoded
Encryption	None by default	Supported via encryption at rest
Typical Use	App settings, URLs, ports	API keys, credentials

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🚀 Common Use Cases

• Environment-specific app settings (MODE=dev, API_URL=https://api.example.com)
• Configuration files (application.properties, .env, JSON, YAML)
• Command-line arguments or script parameters