Applications typically require configuration settings and sensitive information like credentials to function properly. Kubernetes provides two resources specifically designed for this purpose: ConfigMaps for general configuration data and Secrets for sensitive information. In this section, we'll explore how to create, manage, and use these resources effectively.

Understanding ConfigMaps and Secrets

Before diving into the details, let's clarify the purpose of each resource:

ConfigMaps store non-confidential data in key-value pairs. They're ideal for environment-specific settings, configuration files, command-line arguments, etc.
Secrets store sensitive information like passwords, OAuth tokens, and SSH keys. They're similar to ConfigMaps but are specifically intended for confidential data.

Both resources separate configuration from application code, following the Twelve-Factor App methodology's principle of storing configuration in the environment.

Working with ConfigMaps

Let's explore how to create and use ConfigMaps to provide configuration to your applications.

Creating ConfigMaps

There are multiple ways to create ConfigMaps:

From Literal Values

kubectl create configmap app-config \
  --from-literal=APP_ENV=production \
  --from-literal=APP_DEBUG=false \
  --from-literal=APP_PORT=8080

From Files

# Create a properties file
echo "app.env=production" > app.properties
echo "app.debug=false" >> app.properties
echo "app.port=8080" >> app.properties

# Create ConfigMap from the file
kubectl create configmap app-config --from-file=app.properties

From a Directory

# Create a directory with configuration files
mkdir config
echo "This is a config file" > config/config.txt
echo "DB_HOST=localhost" > config/database.env

# Create ConfigMap from the directory
kubectl create configmap app-config --from-file=config/

Using YAML

For more control, you can define a ConfigMap in YAML:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  APP_ENV: production
  APP_DEBUG: 'false'
  APP_PORT: '8080'
  config.json: |
    {
      "database": {
        "host": "db.example.com",
        "port": 5432
      },
      "cache": {
        "enabled": true,
        "ttl": 300
      }
    }
  nginx.conf: |
    server {
      listen 80;
      server_name example.com;
      
      location / {
        proxy_pass http://backend;
      }
    }

Apply this configuration with:

kubectl apply -f app-config.yaml

Viewing ConfigMaps

List all ConfigMaps in the current namespace:

kubectl get configmaps

View the details of a specific ConfigMap:

kubectl describe configmap app-config

To see the actual values:

kubectl get configmap app-config -o yaml

Using ConfigMaps in Pods

ConfigMaps can be used in pods in several ways:

As Environment Variables

apiVersion: v1
kind: Pod
metadata:
  name: config-env-pod
spec:
  containers:
    - name: app
      image: busybox
      command: ['sh', '-c', 'echo $APP_ENV $APP_PORT && sleep 3600']
      env:
        - name: APP_ENV
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: APP_ENV
        - name: APP_PORT
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: APP_PORT

You can also load all keys from a ConfigMap as environment variables:

apiVersion: v1
kind: Pod
metadata:
  name: config-env-all-pod
spec:
  containers:
    - name: app
      image: busybox
      command: ['sh', '-c', 'env | grep APP && sleep 3600']
      envFrom:
        - configMapRef:
            name: app-config

As Files in a Volume

apiVersion: v1
kind: Pod
metadata:
  name: config-vol-pod
spec:
  containers:
    - name: app
      image: busybox
      command: ['sh', '-c', 'cat /config/config.json && sleep 3600']
      volumeMounts:
        - name: config-volume
          mountPath: /config
  volumes:
    - name: config-volume
      configMap:
        name: app-config

You can also mount specific keys:

volumes:
  - name: config-volume
    configMap:
      name: app-config
      items:
        - key: config.json
          path: app/config.json
        - key: nginx.conf
          path: nginx/nginx.conf

As Command-line Arguments

apiVersion: v1
kind: Pod
metadata:
  name: config-arg-pod
spec:
  containers:
    - name: app
      image: busybox
      command: ['echo']
      args: ['$(APP_PORT)']
      env:
        - name: APP_PORT
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: APP_PORT

Working with Secrets

Secrets are similar to ConfigMaps but are designed for confidential data. Kubernetes provides some additional protection for Secrets:

Secrets are stored in a temporary filesystem (tmpfs) in memory, not written to disk
Etcd encrypts Secrets (if encryption is enabled)
Access to Secrets can be restricted with RBAC

However, it's important to note that Secrets are encoded in base64, not encrypted by default. For true encryption at rest, you need to configure encryption.

Creating Secrets

Like ConfigMaps, there are multiple ways to create Secrets:

From Literal Values

kubectl create secret generic db-credentials \
  --from-literal=username=admin \
  --from-literal=password=s3cr3t

From Files

# Create files with sensitive data
echo -n "admin" > username.txt
echo -n "s3cr3t" > password.txt

# Create Secret from files
kubectl create secret generic db-credentials \
  --from-file=username=username.txt \
  --from-file=password=password.txt

Using YAML

If you define Secrets in YAML, you need to encode values in base64:

echo -n "admin" | base64
# Output: YWRtaW4=

echo -n "s3cr3t" | base64
# Output: czNjcjN0

Then create the Secret definition:

apiVersion: v1
kind: Secret
metadata:
  name: db-credentials
type: Opaque
data:
  username: YWRtaW4=
  password: czNjcjN0

You can also use the stringData field, which accepts unencoded strings:

apiVersion: v1
kind: Secret
metadata:
  name: db-credentials
type: Opaque
stringData:
  username: admin
  password: s3cr3t

Secret Types

Kubernetes provides built-in types for common Secret use cases:

Opaque (default): Arbitrary user-defined data
kubernetes.io/tls: TLS certificate and private key
kubernetes.io/dockerconfigjson: Docker registry credentials
kubernetes.io/service-account-token: Service account token
kubernetes.io/basic-auth: Basic authentication credentials
kubernetes.io/ssh-auth: SSH credentials

For example, to create a TLS Secret:

kubectl create secret tls tls-secret --cert=path/to/tls.cert --key=path/to/tls.key

For Docker registry credentials:

kubectl create secret docker-registry regcred \
  --docker-server=registry.example.com \
  --docker-username=username \
  --docker-password=password \
  --docker-email=email@example.com

Viewing Secrets

List all Secrets in the current namespace:

kubectl get secrets

View the details of a specific Secret:

kubectl describe secret db-credentials

To see the actual values (they'll be base64 encoded):

kubectl get secret db-credentials -o yaml

To decode a specific value:

kubectl get secret db-credentials -o jsonpath='{.data.password}' | base64 --decode

Using Secrets in Pods

Secrets can be used in pods similarly to ConfigMaps:

As Environment Variables

apiVersion: v1
kind: Pod
metadata:
  name: secret-env-pod
spec:
  containers:
    - name: app
      image: postgres:13
      env:
        - name: POSTGRES_USER
          valueFrom:
            secretKeyRef:
              name: db-credentials
              key: username
        - name: POSTGRES_PASSWORD
          valueFrom:
            secretKeyRef:
              name: db-credentials
              key: password

You can also load all keys from a Secret:

envFrom:
  - secretRef:
      name: db-credentials

As Files in a Volume

apiVersion: v1
kind: Pod
metadata:
  name: secret-vol-pod
spec:
  containers:
    - name: app
      image: busybox
      command: ['sh', '-c', 'cat /etc/credentials/username && sleep 3600']
      volumeMounts:
        - name: secret-volume
          mountPath: /etc/credentials
  volumes:
    - name: secret-volume
      secret:
        secretName: db-credentials

Using Docker Registry Secrets

apiVersion: v1
kind: Pod
metadata:
  name: private-image-pod
spec:
  containers:
    - name: app
      image: registry.example.com/private/app:1.0
  imagePullSecrets:
    - name: regcred

Updating ConfigMaps and Secrets

When you update a ConfigMap or Secret, the changes are not automatically reflected in pods that already use them.

Environment Variables

Environment variables set from ConfigMaps or Secrets are only evaluated once at pod creation time. To pick up changes, you need to restart the pods.

Volume Mounts

For volume mounts, Kubernetes updates the mounted files within a few minutes. However, applications need to watch for changes or be restarted to detect them.

Updating Strategies

To update your applications when configurations change:

Use deployments with rolling updates:

spec:
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
      maxSurge: 1

Trigger updates by changing pod specifications:

# Create a new version of the ConfigMap
kubectl create configmap app-config-v2 --from-literal=APP_VERSION=2.0

# Update the deployment to use the new ConfigMap
kubectl set env deployment/app-deployment --from=configmap/app-config-v2

Use immutable ConfigMaps and version them:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config-v2
immutable: true
data:
  APP_VERSION: '2.0'

Managing Secrets Securely

While Kubernetes Secrets provide basic functionality for handling sensitive data, production environments often require additional security measures:

1. Enable Encryption at Rest

Configure encryption for etcd storage:

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - aescbc:
          keys:
            - name: key1
              secret: <base64-encoded-key>
      - identity: {}

2. Use External Secret Management Systems

Integration with external secret management tools provides enhanced security. Options include:

HashiCorp Vault: Use the Vault Operator or CSI driver
AWS Secrets Manager: Use External Secrets Operator or ASCP
Azure Key Vault: Use AKV Provider for Secrets Store CSI Driver
Google Secret Manager: Use Secret Manager Operator

Example with External Secrets Operator:

apiVersion: external-secrets.io/v1alpha1
kind: ExternalSecret
metadata:
  name: database-credentials
spec:
  refreshInterval: 1h
  secretStoreRef:
    name: vault-backend
    kind: ClusterSecretStore
  target:
    name: db-credentials
  data:
    - secretKey: username
      remoteRef:
        key: database/credentials
        property: username
    - secretKey: password
      remoteRef:
        key: database/credentials
        property: password

3. Implement RBAC Controls

Restrict access to Secrets with Role-Based Access Control:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: secret-reader
  namespace: default
rules:
  - apiGroups: ['']
    resources: ['secrets']
    verbs: ['get', 'list']
    resourceNames: ['db-credentials']
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: read-secrets
  namespace: default
subjects:
  - kind: User
    name: jane
    apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: Role
  name: secret-reader
  apiGroup: rbac.authorization.k8s.io

4. Use Sealed Secrets

Sealed Secrets (by Bitnami) allows you to encrypt your secrets so they can be safely stored in git:

# Install kubeseal
brew install kubeseal  # For macOS

# Encrypt a secret
kubectl create secret generic db-credentials \
  --from-literal=username=admin \
  --from-literal=password=s3cr3t \
  --dry-run=client -o yaml | \
  kubeseal --format yaml > sealed-secret.yaml

# Apply the sealed secret
kubectl apply -f sealed-secret.yaml

Common Patterns and Use Cases

Configuration Files for Applications

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  application.yml: |
    server:
      port: 8080
    spring:
      datasource:
        url: jdbc:postgresql://db:5432/app
        username: ${DB_USER}
        password: ${DB_PASSWORD}
      jpa:
        hibernate:
          ddl-auto: update
---
apiVersion: v1
kind: Deployment
metadata:
  name: app-deployment
spec:
  replicas: 3
  template:
    spec:
      containers:
        - name: app
          image: myapp:1.0
          volumeMounts:
            - name: config-volume
              mountPath: /app/config
          env:
            - name: DB_USER
              valueFrom:
                secretKeyRef:
                  name: db-credentials
                  key: username
            - name: DB_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: db-credentials
                  key: password
      volumes:
        - name: config-volume
          configMap:
            name: app-config

Feature Flags

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
data:
  ENABLE_NEW_UI: 'true'
  ENABLE_BETA_FEATURES: 'false'
  MAINTENANCE_MODE: 'false'
---
apiVersion: v1
kind: Deployment
metadata:
  name: app-deployment
spec:
  template:
    spec:
      containers:
        - name: app
          image: myapp:1.0
          envFrom:
            - configMapRef:
                name: feature-flags

Environment-Specific Configuration

Create a ConfigMap for each environment and select the appropriate one based on a label:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config-dev
  labels:
    env: dev
data:
  APP_ENV: development
  API_URL: http://api-dev
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config-prod
  labels:
    env: prod
data:
  APP_ENV: production
  API_URL: http://api
---
apiVersion: v1
kind: Deployment
metadata:
  name: app-deployment
spec:
  template:
    spec:
      containers:
        - name: app
          image: myapp:1.0
          envFrom:
            - configMapRef:
                name: app-config-prod # Change based on environment

Best Practices for ConfigMaps and Secrets

Separate configs by concern: Create different ConfigMaps and Secrets for different aspects of your application.
Version your configurations: Use naming conventions that include versions or timestamps.
Keep Secrets minimal: Store only what needs to be kept secret in Secrets; use ConfigMaps for everything else.
Consider the immutable flag: For configs that shouldn't change without redeployment.
Use projectioned volumes: When you need to combine multiple ConfigMaps or Secrets:

volumes:
  - name: all-config
    projected:
      sources:
        - configMap:
            name: app-config
        - secret:
            name: app-secrets
        - configMap:
            name: shared-config

Set up default values: Make your application resilient to missing configuration.
Validate configurations: Implement validation to catch misconfigurations early.
Document your configuration options: Create documentation for all available settings.
Audit Secret access: Monitor and log access to sensitive configuration.
Consider GitOps workflows: Use tools like Flux or ArgoCD with encrypted Secrets.

Using DigitalOcean for Secure Configuration Management

When running Kubernetes in a production environment, properly managing configurations and secrets becomes even more important. DigitalOcean Kubernetes provides a reliable platform with features that help with secure configuration management:

Integration with container registry for private images
Support for external secret management systems
Encrypted etcd for secure storage

In the next section, we'll explore persistent storage in Kubernetes, which allows your applications to store data beyond the container lifecycle.

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