ArgoCD ApplicationSet 컨트롤러 심층 분석

ApplicationSet Controller
    |
    +-- Generator: Application 목록 생성을 위한 데이터 소스
    |
    +-- Template: Application 리소스의 템플릿
    |
    +-- Sync Policy: Application 생성/삭제/업데이트 정책

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: my-appset
  namespace: argocd
spec:
  generators:
    - list:
        elements:
          - cluster: staging
            url: https://staging.example.com
          - cluster: production
            url: https://production.example.com
  template:
    metadata:
      name: 'myapp-{{cluster}}'
    spec:
      project: default
      source:
        repoURL: https://github.com/org/myapp.git
        targetRevision: HEAD
        path: 'overlays/{{cluster}}'
      destination:
        server: '{{url}}'
        namespace: myapp

spec:
  generators:
    - list:
        elements:
          - cluster: staging
            url: https://staging.example.com
            revision: develop
          - cluster: production
            url: https://production.example.com
            revision: main

spec:
  generators:
    - clusters:
        selector:
          matchLabels:
            env: production
            region: ap-northeast-2

# 로컬 클러스터를 포함하려면 명시적으로 설정
spec:
  generators:
    - clusters:
        selector:
          matchLabels:
            env: production
        # 값이 비어있는 셀렉터는 모든 클러스터 매칭 (로컬 포함)

spec:
  generators:
    - git:
        repoURL: https://github.com/org/gitops-config.git
        revision: HEAD
        directories:
          - path: apps/*
          - path: apps/excluded-app
            exclude: true

gitops-config/
  apps/
    frontend/
      kustomization.yaml
    backend/
      kustomization.yaml
    database/
      kustomization.yaml

spec:
  generators:
    - git:
        repoURL: https://github.com/org/gitops-config.git
        revision: HEAD
        files:
          - path: 'clusters/*/config.json'

{
  "cluster": {
    "name": "production-east",
    "server": "https://prod-east.example.com",
    "environment": "production",
    "region": "us-east-1"
  }
}

template:
  metadata:
    name: 'app-{{cluster.name}}'
  spec:
    destination:
      server: '{{cluster.server}}'

spec:
  generators:
    - matrix:
        generators:
          # Generator 1: 클러스터 목록
          - clusters:
              selector:
                matchLabels:
                  env: production
          # Generator 2: 앱 디렉토리 목록
          - git:
              repoURL: https://github.com/org/apps.git
              revision: HEAD
              directories:
                - path: apps/*

(cluster=prod-east, path=apps/frontend)
(cluster=prod-east, path=apps/backend)
(cluster=prod-west, path=apps/frontend)
(cluster=prod-west, path=apps/backend)

spec:
  generators:
    - merge:
        mergeKeys:
          - server
        generators:
          # 기본 Generator: 모든 클러스터
          - clusters:
              values:
                replicas: '3'
                env: default
          # 오버라이드 Generator: 특정 클러스터 설정
          - list:
              elements:
                - server: https://production.example.com
                  values.replicas: '5'
                  values.env: production

spec:
  generators:
    - pullRequest:
        github:
          owner: myorg
          repo: myapp
          labels:
            - preview
        requeueAfterSeconds: 60
  template:
    metadata:
      name: 'preview-{{branch}}-{{number}}'
    spec:
      source:
        repoURL: https://github.com/myorg/myapp.git
        targetRevision: '{{head_sha}}'
        path: deploy/preview
      destination:
        server: https://kubernetes.default.svc
        namespace: 'preview-{{number}}'

spec:
  generators:
    - scmProvider:
        github:
          organization: myorg
          allBranches: false
        filters:
          - repositoryMatch: '^gitops-.*'
            pathsExist:
              - deploy/kustomization.yaml

template:
  metadata:
    name: 'app-{{cluster}}-{{path.basename}}'
    labels:
      env: '{{values.env}}'
  spec:
    source:
      repoURL: '{{url}}'
      path: '{{path}}'
    destination:
      server: '{{server}}'
      namespace: '{{namespace}}'

spec:
  goTemplate: true
  goTemplateOptions: ['missingkey=error']
  template:
    metadata:
      name: 'app-{{ .cluster | lower }}'
    spec:
      source:
        path: '{{ if eq .env "production" }}overlays/prod{{ else }}overlays/dev{{ end }}'

spec:
  strategy:
    type: RollingSync
    rollingSync:
      steps:
        - matchExpressions:
            - key: env
              operator: In
              values:
                - staging
          maxUpdate: 100% # staging 환경 먼저 전부 업데이트
        - matchExpressions:
            - key: env
              operator: In
              values:
                - production
          maxUpdate: 25% # production은 25%씩 업데이트

Step 1: staging 레이블이 있는 모든 Application 동기화
  -> 모든 Application이 Healthy가 될 때까지 대기

Step 2: production 레이블이 있는 Application 중 25%만 동기화
  -> Healthy 확인 후 다음 25% 진행
  -> 모든 production Application이 완료될 때까지 반복

spec:
  generators:
    - clusterDecisionResource:
        configMapRef: my-placement-decision
        name: placement-decision
        requeueAfterSeconds: 180

반복:
  1. 모든 ApplicationSet 리소스 감시 (Informer)
  2. 각 ApplicationSet에 대해:
     a. Generator 실행하여 파라미터 집합 생성
     b. 템플릿을 렌더링하여 원하는 Application 목록 생성
     c. 현재 존재하는 Application 목록 조회
     d. 비교하여:
        - 새로 추가할 Application 생성
        - 변경된 Application 업데이트
        - 제거 대상 Application 삭제 (정책에 따라)
  3. requeueAfterSeconds 후 재실행

spec:
  generators:
    - pullRequest:
        github:
          owner: myorg
          repo: myapp
        requeueAfterSeconds: 60 # 60초마다 PR 상태를 다시 확인

spec:
  syncPolicy:
    preserveResourcesOnDeletion: false # ApplicationSet 삭제 시 Application도 삭제

spec:
  syncPolicy:
    preserveResourcesOnDeletion: true # ApplicationSet 삭제해도 Application 유지

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: platform-services
  namespace: argocd
spec:
  generators:
    - matrix:
        generators:
          - clusters:
              selector:
                matchLabels:
                  tier: production
          - git:
              repoURL: https://github.com/org/platform.git
              revision: HEAD
              directories:
                - path: services/*
  template:
    metadata:
      name: '{{name}}-{{path.basename}}'
    spec:
      project: platform
      source:
        repoURL: https://github.com/org/platform.git
        targetRevision: HEAD
        path: '{{path}}'
      destination:
        server: '{{server}}'
        namespace: '{{path.basename}}'
      syncPolicy:
        automated:
          prune: true
          selfHeal: true
        syncOptions:
          - CreateNamespace=true

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: preview-envs
  namespace: argocd
spec:
  generators:
    - pullRequest:
        github:
          owner: myorg
          repo: myapp
          labels:
            - deploy-preview
        requeueAfterSeconds: 30
  template:
    metadata:
      name: 'preview-{{number}}'
      annotations:
        preview-url: 'https://pr-{{number}}.preview.example.com'
    spec:
      project: previews
      source:
        repoURL: https://github.com/myorg/myapp.git
        targetRevision: '{{head_sha}}'
        path: deploy/preview
        helm:
          parameters:
            - name: ingress.host
              value: 'pr-{{number}}.preview.example.com'
            - name: image.tag
              value: '{{head_short_sha}}'
      destination:
        server: https://kubernetes.default.svc
        namespace: 'preview-{{number}}'
      syncPolicy:
        automated:
          prune: true
          selfHeal: true
        syncOptions:
          - CreateNamespace=true

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: app-with-overrides
  namespace: argocd
spec:
  generators:
    - merge:
        mergeKeys:
          - name
        generators:
          - clusters:
              values:
                replicas: '2'
                logLevel: info
          - list:
              elements:
                - name: production-cluster
                  values.replicas: '5'
                  values.logLevel: warn
  template:
    metadata:
      name: 'myapp-{{name}}'
    spec:
      project: default
      source:
        repoURL: https://github.com/org/myapp.git
        targetRevision: HEAD
        path: deploy
        helm:
          parameters:
            - name: replicas
              value: '{{values.replicas}}'
            - name: logLevel
              value: '{{values.logLevel}}'
      destination:
        server: '{{server}}'
        namespace: myapp

# ApplicationSet 상태 확인
kubectl get applicationset -n argocd

# ApplicationSet 상세 정보 확인
kubectl describe applicationset my-appset -n argocd

# ApplicationSet Controller 로그 확인
kubectl logs -n argocd deployment/argocd-applicationset-controller

# 생성된 Application 확인
argocd app list