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Kustomize Integration

Kustomize lets you manage variations of OpenMCF manifests without duplication. Instead of maintaining separate manifest files for dev, staging, and production, you maintain one base manifest and environment-specific overlays that patch the base.

For the conceptual overview of manifest sources (including Kustomize), see Manifests. For flag details, see CLI Reference.

manifests/database/
|-- base/
|   \-- database.yaml      # Shared configuration
\-- overlays/
    |-- dev/
    |-- staging/
    \-- prod/               # Environment-specific patches

OpenMCF integrates Kustomize as a Go library (sigs.k8s.io/kustomize), not as an external binary. The --kustomize-dir and --overlay flags trigger Kustomize to build the final manifest at deployment time.

Quick Start

1. Create Base Manifest

mkdir -p services/api/kustomize/base

services/api/kustomize/base/deployment.yaml:

apiVersion: kubernetes.openmcf.org/v1
kind: KubernetesDeployment
metadata:
  name: api
spec:
  container:
    image:
      repo: myapp/api
      tag: latest
    replicas: 1
    resources:
      limits:
        cpu: 500m
        memory: 512Mi

services/api/kustomize/base/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - deployment.yaml

2. Create Environment Overlay

services/api/kustomize/overlays/prod/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

patches:
  - path: patch.yaml

services/api/kustomize/overlays/prod/patch.yaml:

apiVersion: kubernetes.openmcf.org/v1
kind: KubernetesDeployment
metadata:
  name: api
spec:
  container:
    image:
      tag: v1.0.0
    replicas: 3
    resources:
      limits:
        cpu: 2000m
        memory: 4Gi

3. Deploy with OpenMCF

# Deploy to production
openmcf pulumi up \
  --kustomize-dir services/api/kustomize \
  --overlay prod

# Deploy to dev
openmcf pulumi up \
  --kustomize-dir services/api/kustomize \
  --overlay dev

What happens:

  1. OpenMCF runs kustomize build services/api/kustomize/overlays/prod
  2. Merges base + prod overlay into final manifest
  3. Validates the result
  4. Deploys using Pulumi or OpenTofu

Directory Structure

Standard Layout

<service-name>/kustomize/
|-- base/
|   |-- kustomization.yaml          # Base kustomization config
|   \-- <resource>.yaml             # Base resource definition
\-- overlays/
    |-- dev/
    |   |-- kustomization.yaml      # Dev environment config
    |   \-- patch.yaml              # Dev-specific patches
    |-- staging/
    |   |-- kustomization.yaml
    |   \-- patch.yaml
    \-- prod/
        |-- kustomization.yaml
        \-- patch.yaml

Example: Complete Service

backend/services/api/kustomize/
|-- base/
|   |-- kustomization.yaml
|   |-- deployment.yaml
|   \-- database.yaml
\-- overlays/
    |-- dev/
    |   |-- kustomization.yaml
    |   |-- deployment-patch.yaml
    |   \-- database-patch.yaml
    |-- staging/
    |   |-- kustomization.yaml
    |   |-- deployment-patch.yaml
    |   \-- database-patch.yaml
    \-- prod/
        |-- kustomization.yaml
        |-- deployment-patch.yaml
        \-- database-patch.yaml

Creating Patches

Strategic Merge Patches

The most common approach - specify only the fields you want to change:

Base:

apiVersion: kubernetes.openmcf.org/v1
kind: KubernetesPostgres
metadata:
  name: app-database
spec:
  container:
    replicas: 1
    resources:
      limits:
        cpu: 500m
        memory: 1Gi
    diskSize: 10Gi

Prod Patch (overlays/prod/patch.yaml):

apiVersion: kubernetes.openmcf.org/v1
kind: KubernetesPostgres
metadata:
  name: app-database
spec:
  container:
    replicas: 3              # Override
    resources:
      limits:
        cpu: 2000m           # Override
        memory: 4Gi          # Override
    diskSize: 100Gi          # Override

Result: Base + patch merged = 3 replicas, 2000m CPU, 4Gi memory, 100Gi disk.

JSON 6902 Patches

For more complex changes:

overlays/prod/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

patches:
  - target:
      kind: KubernetesPostgres
      name: app-database
    patch: |-
      - op: replace
        path: /spec/container/replicas
        value: 3
      - op: add
        path: /metadata/labels/environment
        value: production

Common Patterns

Pattern 1: Environment-Specific Resources

Different instance sizes per environment:

Dev (small, cheap):

spec:
  container:
    replicas: 1
    resources:
      limits:
        cpu: 500m
        memory: 512Mi

Prod (large, resilient):

spec:
  container:
    replicas: 5
    resources:
      limits:
        cpu: 2000m
        memory: 4Gi

Pattern 2: Environment-Specific Labels

Add labels for cost tracking:

overlays/prod/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

commonLabels:
  environment: production
  cost-center: engineering
  team: backend

Pattern 3: Environment-Specific Images

overlays/dev/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

images:
  - name: myapp/api
    newTag: latest          # Dev uses latest

patches:
  - path: dev-patch.yaml

overlays/prod/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

images:
  - name: myapp/api
    newTag: v1.2.3          # Prod uses specific version

patches:
  - path: prod-patch.yaml

Pattern 4: Shared Configuration + Environment Patches

base/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

commonLabels:
  app: api
  managed-by: openmcf

resources:
  - deployment.yaml
  - database.yaml
  - cache.yaml

Each resource in base defines shared configuration, overlays patch for environment needs.

Workflow Examples

Deploying to Multiple Environments

# Deploy to dev
openmcf pulumi up \
  --kustomize-dir services/api/kustomize \
  --overlay dev \
  --yes

# Test in dev...

# Deploy to staging
openmcf pulumi up \
  --kustomize-dir services/api/kustomize \
  --overlay staging \
  --yes

# Test in staging...

# Deploy to production (with review)
openmcf pulumi preview \
  --kustomize-dir services/api/kustomize \
  --overlay prod

# Review changes...

openmcf pulumi up \
  --kustomize-dir services/api/kustomize \
  --overlay prod

Combining Kustomize with --set Overrides

# Kustomize overlay + runtime override
openmcf pulumi up \
  --kustomize-dir services/api/kustomize \
  --overlay prod \
  --set spec.container.image.tag=v1.2.4

Order of precedence:

  1. Base manifest
  2. Overlay patches applied
  3. --set overrides applied last (highest priority)

Preview Built Manifest

# See what Kustomize generates (useful for debugging)
cd services/api/kustomize
kustomize build overlays/prod

# Or let OpenMCF build and show it
openmcf load-manifest \
  --kustomize-dir services/api/kustomize \
  --overlay prod

For using Kustomize in CI/CD pipelines with branch-based overlay selection, see CI/CD Integration.

Advanced Techniques

Multiple Bases

Useful for shared components:

common/
\-- base/
    |-- kustomization.yaml
    \-- shared-config.yaml

service-a/kustomize/
\-- overlays/
    \-- prod/
        |-- kustomization.yaml  # References ../../../common/base
        \-- patch.yaml

service-b/kustomize/
\-- overlays/
    \-- prod/
        |-- kustomization.yaml  # Also references ../../../common/base
        \-- patch.yaml

Components (Reusable Pieces)

components/monitoring/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1alpha1
kind: Component

patches:
  - path: add-monitoring.yaml

Use in overlay:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

components:
  - ../../../components/monitoring

Generating ConfigMaps from Files

overlays/prod/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

configMapGenerator:
  - name: app-config
    files:
      - config/prod.yaml
      - config/secrets.encrypted

Troubleshooting

Error: "no such file or directory"

Problem: Kustomize can't find referenced files.

Solution:

# Check file paths in kustomization.yaml
# Ensure paths are relative to kustomization.yaml location

# Verify structure
ls -R services/api/kustomize/

Error: "kustomization.yaml not found"

Problem: Missing kustomization.yaml in overlay.

Solution:

# Create kustomization.yaml
cat > services/api/kustomize/overlays/prod/kustomization.yaml <<EOF
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base
EOF

Patch Not Applied

Problem: Your patch isn't affecting the final output.

Solution:

# 1. Verify patch is listed in kustomization.yaml
cat overlays/prod/kustomization.yaml

# 2. Check patch targets correct resource
# - apiVersion must match
# - kind must match
# - metadata.name must match

# 3. Test kustomize build directly
cd services/api/kustomize
kustomize build overlays/prod

Wrong Overlay Applied

Problem: Deployed dev config to prod (or vice versa).

Solution:

# Always verify overlay before deploying
openmcf pulumi preview \
  --kustomize-dir services/api/kustomize \
  --overlay prod  # Double-check this!

# Use explicit confirmation in CI/CD
if [ "$OVERLAY" != "prod" ]; then
  echo "Deploying to $OVERLAY"
  openmcf pulumi up --kustomize-dir ... --overlay $OVERLAY --yes
else
  echo "Production deployment - manual approval required"
  openmcf pulumi up --kustomize-dir ... --overlay $OVERLAY
fi

Best Practices

1. Keep Base Minimal

# ✅ Good: Base has common configuration
base/deployment.yaml:
  name: api
  container:
    image:
      repo: myapp/api
    # No environment-specific values

# ❌ Bad: Base has production values
base/deployment.yaml:
  name: api
  container:
    replicas: 10  # Production-specific, doesn't belong in base

2. One Overlay Per Environment

# Good
overlays/
|-- dev/
|-- staging/
\-- prod/

# Confusing
overlays/
|-- dev-us-west/
|-- dev-eu-central/
|-- staging-us-west/
\-- ... (too many combinations)

3. Use Descriptive Patch Names

# Good
overlays/prod/
|-- kustomization.yaml
|-- resources-patch.yaml          # Increases resources
|-- replicas-patch.yaml            # Scales replicas
\-- monitoring-patch.yaml          # Adds monitoring

# Bad
overlays/prod/
|-- kustomization.yaml
|-- patch1.yaml
|-- patch2.yaml
\-- patch3.yaml

4. Version Control Everything

# ✅ Good: All kustomize files in Git
git add services/api/kustomize/
git commit -m "feat: add production overlay for API"

# ❌ Bad: Generated files, temp files committed
git add services/api/kustomize/overlays/prod/output.yaml  # Generated

5. Test Overlays Before Deploying

# ✅ Good: Preview before applying
kustomize build overlays/prod | less  # Review output
openmcf pulumi preview --kustomize-dir ... --overlay prod

# ⚠️ Risky: Deploy without review
openmcf pulumi up --kustomize-dir ... --overlay prod --yes

Complete Example

Here's a complete real-world example:

Directory Structure

backend/services/api/kustomize/
|-- base/
|   |-- kustomization.yaml
|   |-- deployment.yaml
|   |-- database.yaml
|   \-- redis.yaml
\-- overlays/
    |-- dev/
    |   |-- kustomization.yaml
    |   |-- deployment-patch.yaml
    |   |-- database-patch.yaml
    |   \-- redis-patch.yaml
    \-- prod/
        |-- kustomization.yaml
        |-- deployment-patch.yaml
        |-- database-patch.yaml
        \-- redis-patch.yaml

Files

base/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

commonLabels:
  app: api
  managed-by: openmcf

resources:
  - deployment.yaml
  - database.yaml
  - redis.yaml

base/deployment.yaml:

apiVersion: kubernetes.openmcf.org/v1
kind: KubernetesDeployment
metadata:
  name: api
spec:
  container:
    image:
      repo: mycompany/api
      tag: latest
    replicas: 1
    resources:
      limits:
        cpu: 500m
        memory: 512Mi

overlays/prod/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

commonLabels:
  environment: production

images:
  - name: mycompany/api
    newTag: v1.0.0

patches:
  - path: deployment-patch.yaml
  - path: database-patch.yaml
  - path: redis-patch.yaml

overlays/prod/deployment-patch.yaml:

apiVersion: kubernetes.openmcf.org/v1
kind: KubernetesDeployment
metadata:
  name: api
spec:
  container:
    replicas: 5
    resources:
      limits:
        cpu: 2000m
        memory: 4Gi

Deployment

# Deploy to production
openmcf pulumi up \
  --kustomize-dir backend/services/api/kustomize \
  --overlay prod

What's Next

  • Writing Manifests — Manifest structure and best practices
  • CI/CD Integration — Kustomize with GitHub Actions and GitLab CI
  • Advanced Usage — Combining Kustomize with --set overrides
  • State Backends — Per-environment state configuration
  • Official Kustomize Docs — Kustomize reference documentation

Next article

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