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Kustomization

Table of Contents​

  1. Concept
  2. Create a Kustomization
  3. Advanced options
  4. Dependencies
  5. Health Checks
  6. Hands-on exercises

1 - Concept​

What is a Flux Kustomization?​

A Flux Kustomization applies Kubernetes manifests from a source (GitRepository).

warning

Do not confuse it with Kustomize's kustomization.yaml. The Flux Kustomization is a CRD that uses the Kustomize Controller.

Workflow​

  1. The Source Controller downloads the repo
  2. The Kustomize Controller reads the specified path
  3. It applies the manifests with kubectl apply
  4. It checks the health of the resources
  5. It loops according to the interval

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2 - Create a Kustomization​

Basic YAML​

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: my-app
  namespace: flux-system
spec:
  interval: 5m
  path: ./apps/my-app
  prune: true
  sourceRef:
    kind: GitRepository
    name: my-repo
  targetNamespace: default

Via CLI​

flux create kustomization my-app \
  --source=GitRepository/my-repo \
  --path="./apps/my-app" \
  --prune=true \
  --interval=5m \
  --target-namespace=default

With Kustomize overlays​

# Structure du repo
apps/my-app/
├── base/
│   ├── kustomization.yaml
│   ├── deployment.yaml
│   └── service.yaml
└── overlays/
    ├── dev/
    │   └── kustomization.yaml
    └── prod/
        └── kustomization.yaml
# Flux Kustomization pour prod
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: my-app-prod
  namespace: flux-system
spec:
  interval: 5m
  path: ./apps/my-app/overlays/prod
  prune: true
  sourceRef:
    kind: GitRepository
    name: my-repo

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3 - Advanced options​

Prune (automatic deletion)​

spec:
  prune: true  # Supprime les ressources orphelines

Force (recreate if necessary)​

spec:
  force: true  # Recréer au lieu de patcher

Variable substitution​

spec:
  postBuild:
    substitute:
      ENVIRONMENT: production
      REPLICAS: "5"
    substituteFrom:
      - kind: ConfigMap
        name: cluster-config
      - kind: Secret
        name: cluster-secrets
# Dans le manifest
apiVersion: apps/v1
kind: Deployment
spec:
  replicas: ${REPLICAS}
  template:
    spec:
      containers:
        - name: app
          env:
            - name: ENV
              value: ${ENVIRONMENT}

Inline patches​

spec:
  patches:
    - patch: |
        apiVersion: apps/v1
        kind: Deployment
        metadata:
          name: my-app
        spec:
          replicas: 3
      target:
        kind: Deployment
        name: my-app

Images​

spec:
  images:
    - name: nginx
      newName: my-registry/nginx
      newTag: v1.2.3

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4 - Dependencies​

dependsOn​

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: app
  namespace: flux-system
spec:
  dependsOn:
    - name: infrastructure  # Déployer infra d'abord
    - name: secrets
  interval: 5m
  path: ./apps/my-app
  sourceRef:
    kind: GitRepository
    name: my-repo

Deployment order​

# infrastructure.yaml
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: infrastructure
spec:
  path: ./infrastructure
  ...
---
# database.yaml
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: database
spec:
  dependsOn:
    - name: infrastructure
  path: ./apps/database
  ...
---
# backend.yaml
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: backend
spec:
  dependsOn:
    - name: database
  path: ./apps/backend
  ...

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5 - Health Checks​

healthChecks​

spec:
  healthChecks:
    - apiVersion: apps/v1
      kind: Deployment
      name: my-app
      namespace: default
  timeout: 3m

wait​

spec:
  wait: true  # Attendre que toutes les ressources soient prêtes
  timeout: 5m

Retry​

spec:
  retryInterval: 1m  # Réessayer si échec

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6 - Hands-on exercises​

Exercise 1: Deploy podinfo​

# 1. Créer la source
flux create source git podinfo \
  --url=https://github.com/stefanprodan/podinfo \
  --branch=master

# 2. Créer la Kustomization
flux create kustomization podinfo \
  --source=GitRepository/podinfo \
  --path="./kustomize" \
  --prune=true \
  --interval=5m \
  --target-namespace=default

# 3. Vérifier
flux get kustomizations
kubectl get pods

Exercise 2: Declarative YAML​

# podinfo.yaml
apiVersion: source.toolkit.fluxcd.io/v1
kind: GitRepository
metadata:
  name: podinfo
  namespace: flux-system
spec:
  interval: 1m
  url: https://github.com/stefanprodan/podinfo
  ref:
    branch: master
---
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: podinfo
  namespace: flux-system
spec:
  interval: 5m
  path: ./kustomize
  prune: true
  sourceRef:
    kind: GitRepository
    name: podinfo
  targetNamespace: default

Quiz​

Q1. What does prune: true do?

Answer

prune: true automatically deletes the Kubernetes resources that are no longer present in Git. If you delete a file from the repo, the corresponding resource will be deleted from the cluster.

Q2. How do you ensure that an app is deployed after the database?

Answer

Use dependsOn:

spec:
  dependsOn:
    - name: database

The Kustomization waits for database to be Healthy before deploying.

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Key takeaways​

  • Flux Kustomization ≠ Kustomize's kustomization.yaml
  • sourceRef points to a GitRepository
  • path indicates the path in the repo
  • prune: true to clean up orphans
  • dependsOn for deployment order
  • Variables with postBuild.substitute

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