Format and Validate Kubernetes YAML Manifests

Kubernetes YAML Formatting

Kubernetes uses YAML as its primary configuration language. Every resource — Deployments, Services, ConfigMaps, Ingresses — is defined in YAML manifests. Proper formatting is essential because Kubernetes is strict about YAML structure.

Anatomy of a Kubernetes Manifest

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-server
  namespace: production
  labels:
    app: web-server
    tier: frontend
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-server
  template:
    metadata:
      labels:
        app: web-server
    spec:
      containers:
        - name: nginx
          image: nginx:1.25
          ports:
            - containerPort: 80
          resources:
            requests:
              memory: "64Mi"
              cpu: "250m"
            limits:
              memory: "128Mi"
              cpu: "500m"

Common Formatting Issues

1. Inconsistent indentation — Mixing 2-space and 4-space indentation within a single manifest
2. Tab characters — Kubernetes rejects YAML with tabs; only spaces are allowed
3. Trailing whitespace — Can cause unexpected diffs in version control
4. Missing --- separators — Multi-resource files need document separators between resources
5. Quoted vs. unquoted values — Resource limits like "250m" need quotes to avoid being parsed as numbers

Multi-Resource Files

Kubernetes manifests often contain multiple resources in a single file, separated by ---:

apiVersion: v1
kind: Service
metadata:
  name: web-server
spec:
  selector:
    app: web-server
  ports:
    - port: 80
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-server
# ...

A YAML formatter must handle multi-document files correctly, formatting each document independently while preserving the --- separators.

Best Practices

• Use 2-space indentation (Kubernetes ecosystem standard)
• Always quote string values that look like numbers or booleans
• Use --- to separate multiple resources
• Run kubectl apply --dry-run=client after formatting to validate