KUBERNETES: TỪ CƠ BẢN ĐẾN NÂNG CAO

Module 9: Cluster Management

xdev.asia

🎯 Mục tiêu bài học

Hiểu Cluster API — cách quản lý K8s clusters như K8s objects. Tìm hiểu ClusterClass, Machine management, và so sánh với các IaC approaches khác (Terraform, Crossplane).

1. Cluster API là gì?

Cluster API (CAPI) là Kubernetes project cho phép quản lý lifecycle của Kubernetes clusters sử dụng Kubernetes API — "Kubernetes để tạo Kubernetes".

Các khái niệm chính:

• Management Cluster: cluster chạy CAPI controllers, quản lý các workload clusters
• Workload Cluster: cluster được tạo và quản lý bởi CAPI
• Infrastructure Provider: AWS (CAPA), GCP (CAPG), Azure (CAPZ), vSphere (CAPV)
• Bootstrap Provider: kubeadm (KubeadmControlPlane), RKE2

2. CAPI Core Resources

# Cluster: đại diện cho một workload cluster
apiVersion: cluster.x-k8s.io/v1beta1
kind: Cluster
metadata:
  name: production-cluster
  namespace: default
spec:
  clusterNetwork:
    pods:
      cidrBlocks: ["10.0.0.0/16"]
    services:
      cidrBlocks: ["10.96.0.0/12"]
  # Reference tới infrastructure provider (AWS/GCP/etc)
  infrastructureRef:
    apiVersion: infrastructure.cluster.x-k8s.io/v1beta2
    kind: AWSCluster
    name: production-cluster
  # Reference tới control plane provider
  controlPlaneRef:
    apiVersion: controlplane.cluster.x-k8s.io/v1beta1
    kind: KubeadmControlPlane
    name: production-cluster-control-plane

# MachineDeployment: quản lý worker nodes (giống Deployment cho VMs)
apiVersion: cluster.x-k8s.io/v1beta1
kind: MachineDeployment
metadata:
  name: production-workers
spec:
  clusterName: production-cluster
  replicas: 3
  selector:
    matchLabels:
      cluster.x-k8s.io/cluster-name: production-cluster
  template:
    spec:
      bootstrap:
        configRef:
          apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
          kind: KubeadmConfigTemplate
          name: production-worker-config
      infrastructureRef:
        apiVersion: infrastructure.cluster.x-k8s.io/v1beta2
        kind: AWSMachineTemplate
        name: production-worker-machine
      version: "v1.32.0"

3. ClusterClass — Template cho Clusters

ClusterClass (CAPI v1.4+) cho phép định nghĩa template chuẩn để tạo nhiều clusters từ một spec:

apiVersion: cluster.x-k8s.io/v1beta1
kind: ClusterClass
metadata:
  name: aws-production-class
spec:
  controlPlane:
    ref:
      apiVersion: controlplane.cluster.x-k8s.io/v1beta1
      kind: KubeadmControlPlaneTemplate
      name: aws-cp-template
    machineInfrastructure:
      ref:
        apiVersion: infrastructure.cluster.x-k8s.io/v1beta2
        kind: AWSMachineTemplate
        name: aws-cp-machine-template
  infrastructure:
    ref:
      apiVersion: infrastructure.cluster.x-k8s.io/v1beta2
      kind: AWSClusterTemplate
      name: aws-cluster-template
  workers:
    machineDeployments:
    - class: default-worker
      template:
        bootstrap:
          ref:
            apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
            kind: KubeadmConfigTemplate
            name: worker-bootstrap
        infrastructure:
          ref:
            apiVersion: infrastructure.cluster.x-k8s.io/v1beta2
            kind: AWSMachineTemplate
            name: aws-worker-template
  # Variables có thể customize per-cluster
  variables:
  - name: region
    required: true
    schema:
      openAPIV3Schema:
        type: string
  - name: instanceType
    schema:
      openAPIV3Schema:
        type: string
        default: m5.xlarge

# Tạo cluster từ ClusterClass
apiVersion: cluster.x-k8s.io/v1beta1
kind: Cluster
metadata:
  name: team-alpha-cluster
spec:
  topology:
    class: aws-production-class
    version: v1.32.0
    controlPlane:
      replicas: 3
    workers:
      machineDeployments:
      - name: workers
        replicas: 5
    variables:
    - name: region
      value: ap-southeast-1
    - name: instanceType
      value: c5.2xlarge

4. Cài đặt CAPI

# Cài clusterctl CLI
curl -L https://github.com/kubernetes-sigs/cluster-api/releases/latest/download/clusterctl-linux-amd64 -o /usr/local/bin/clusterctl
chmod +x /usr/local/bin/clusterctl
Init management cluster (ví dụ AWS provider)
export AWS_REGION=ap-southeast-1
export AWS_ACCESS_KEY_ID=...
export AWS_SECRET_ACCESS_KEY=...
export AWS_SESSION_TOKEN=...      # nếu dùng MFA
Prepare AWS credentials
clusterawsadm bootstrap iam create-cloudformation-stack
export AWS_B64ENCODED_CREDENTIALS=$(clusterawsadm bootstrap credentials encode-as-profile)
Init CAPI
clusterctl init --infrastructure aws
Verify
kubectl get pods -n capi-system
kubectl get pods -n capa-system   # AWS provider
Xem providers
clusterctl describe provider

5. Tạo và Quản lý Clusters

# Generate cluster manifest từ template
clusterctl generate cluster production-cluster \
  --infrastructure aws \
  --kubernetes-version v1.32.0 \
  --control-plane-machine-count 3 \
  --worker-machine-count 5 \
  > production-cluster.yaml
Apply
kubectl apply -f production-cluster.yaml
Theo dõi provisioning
clusterctl describe cluster production-cluster
kubectl get machines -A -w
Lấy kubeconfig của workload cluster
clusterctl get kubeconfig production-cluster > production.kubeconfig
Upgrade workload cluster
kubectl patch cluster production-cluster --patch '{"spec": {"topology": {"version": "v1.33.0"}}}' --type merge
Scale worker nodes
kubectl patch machinedeployment production-workers --patch '{"spec": {"replicas": 10}}' --type merge
Delete cluster (tất cả VMs, LBs sẽ được dọn dẹp)
kubectl delete cluster production-cluster

6. Crossplane — Control Plane Framework

Crossplane là alternative/complement cho CAPI — quản lý cloud resources (không chỉ clusters) bằng Kubernetes CRDs:

# Cài Crossplane
helm repo add crossplane-stable https://charts.crossplane.io/stable
helm install crossplane crossplane-stable/crossplane -n crossplane-system --create-namespace
Cài AWS provider
kubectl apply -f - <<EOF
apiVersion: pkg.crossplane.io/v1
kind: Provider
metadata:
name: provider-aws-ec2
spec:
package: xpkg.upbound.io/upbound/provider-aws-ec2:latest
EOF

# Tạo RDS instance bằng Crossplane
apiVersion: rds.aws.upbound.io/v1beta1
kind: Instance
metadata:
  name: my-postgres
spec:
  forProvider:
    region: ap-southeast-1
    instanceClass: db.t3.medium
    engine: postgres
    engineVersion: "16.3"
    allocatedStorage: 20
    username: admin
    skipFinalSnapshot: true
  writeConnectionSecretToRef:
    namespace: default
    name: my-postgres-conn     # K8s Secret với connection info

7. IaC Comparison 2026

Tool        Use Case                          Approach
──────────────────────────────────────────────────────────────
Terraform   Multi-cloud infra provisioning    HCL, state file
Pulumi      Infra as code với real languages  Python/TS/Go
CAPI        K8s cluster lifecycle             K8s API, GitOps-friendly
Crossplane  Cloud resources via K8s API       K8s API, Composition
Helm        K8s app deployment                Templates, values
Kustomize   K8s manifest overlay              Patch-based, no templates
2026 Trend: CAPI + Crossplane combination
- CAPI: quản lý cluster lifecycle
- Crossplane: quản lý cloud resources (RDS, S3, etc.) được tham chiếu bởi apps
- ArgoCD/Flux: deploy tất cả qua GitOps

Tóm tắt

• Cluster API: quản lý K8s cluster lifecycle bằng K8s objects
• ClusterClass: template chuẩn để tạo nhiều clusters consistent
• Management cluster + Workload clusters: tách biệt rõ ràng
• Crossplane: quản lý cloud resources (DB, storage, network) bằng K8s CRDs
• CAPI + Crossplane + ArgoCD: full GitOps platform engineering stack 2026