Declarative Setup App of Apps

In this lesson, you’ll learn how to extend ArgoCD’s declarative application approach by deploying multiple applications using the “app-of-apps” pattern. In this model, a single ArgoCD application manages other ArgoCD applications, streamlining the deployment and management of multiple services. The repository structure for this setup organizes multiple ArgoCD configurations into separate directories, each containing the manifest files for individual applications.

Multi-App ArgoCD Application

The primary multi-app ArgoCD application points to the Git repository and specifies the path containing the manifests that manage other ArgoCD applications. Its definition is shown below:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: app-of-apps
  namespace: argocd
spec:
  project: default
  source:
    repoURL: http://165.22.209.118:3000/siddharth/gitops-argocd.git
    targetRevision: HEAD
    path: ./declarative/multi-app
  destination:
    server: https://kubernetes.default.svc
    namespace: argocd
  syncPolicy:
    automated:
      prune: true
      selfHeal: true

The multi-app configuration retrieves manifests from a specific directory, providing a centralized configuration for managing nested applications.

App of Apps Configuration

The primary application references the “app-of-apps” directory, where multiple ArgoCD application manifests reside. The configuration for the app-of-apps is as follows:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: app-of-apps
  namespace: argocd
spec:
  project: default
  source:
    repoURL: http://165.22.209.118:3000/siddharth/gitops-argocd.git
    targetRevision: HEAD
    path: ./declarative/app-of-apps
  destination:
    server: https://kubernetes.default.svc
    namespace: argocd
  syncPolicy:
    automated:
      prune: true
      selfHeal: true

Inside the declarative/app-of-apps directory, you will find three ArgoCD application manifests:

Heliocentric App – Retrieves Kubernetes manifests from a specified manifest path.
Geocentric App – Points to a different manifest path.
Additional Applications – You can add more sub-applications to extend deployment capabilities further.

Heliocentric App Manifest

The following example shows the manifest for the Heliocentric application:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: heliocentric-app
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io
spec:
  project: default
  source:
    repoURL: http://165.22.209.118:3000/siddharth/gitops-argocd.git
    targetRevision: HEAD
    path: ./declarative/manifests/heliocentric-model
  destination:
    server: https://kubernetes.default.svc
    namespace: heliocentric
  syncPolicy:
    syncOptions:
      - CreateNamespace=true
    automated:
      prune: true
      selfHeal: true

Geocentric App Manifest

The Geocentric application manifest is configured similarly:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: geocentric-app
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io
spec:
  project: default
  source:
    repoURL: http://165.22.209.118:3000/siddharth/gitops-argocd.git
    targetRevision: HEAD
    path: ./declarative/manifests/geocentric-model
  destination:
    server: https://kubernetes.default.svc
    namespace: geocentric
  syncPolicy:
    syncOptions:
      - CreateNamespace=true
    automated:
      prune: true
      selfHeal: true

Kubernetes Application Manifests

Beyond the ArgoCD application manifests, the declarative directory also contains separate Kubernetes manifests for individual applications, including deployments and services. When you create the main app-of-apps ArgoCD application, it automatically triggers the creation of three more ArgoCD applications. For example, an alternative app-of-apps manifest with a different destination namespace might be defined as:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: app-of-apps
  namespace: argocd
spec:
  project: default
  source:
    repoURL: http://165.22.209.118:3000/siddharth/gitops-argocd.git
    targetRevision: HEAD
    path: ./declarative/app-of-apps
  destination:
    server: https://kubernetes.default.svc
    namespace: kubernetes
  syncPolicy:
    automated:
      prune: true
      selfHeal: true

Each nested application then deploys its respective Kubernetes resources based on its individual manifest.

Deployment Process

To deploy applications using the app-of-apps pattern, follow these steps:

Delete any previously deployed Geocentric model application if it exists, since it will be recreated under the new management pattern.
Navigate to the multi-app directory, which contains the app-of-apps.yml file.

Apply the manifest in the argocd namespace by running:

cd multi-app/
ll
# Ensure the app-of-apps.yml file is present here.
k -n argocd apply -f app-of-apps.yml

After deployment, the ArgoCD UI will display multiple applications:

app-of-apps (managing the nested applications)
geocentric-app
heliocentric-app
heliocentric-app with no Pluto (an alternative variant)

Ensure that no old configurations interfere with the new deployment by removing outdated applications before applying the new manifest.

Viewing the Applications in the ArgoCD UI

Within the ArgoCD dashboard, clicking on any sub-application (e.g., geocentric-app or heliocentric-app) provides detailed manifest information. Below is an example manifest snippet for a syncing application:

status:
  health:
    status: Healthy
  history:
    deployStartDate: '2022-09-23T20:05:21Z'
    deployEndDate: '2022-09-23T20:05:24Z'
    revision: e2edb3a016b752028c38adb898d34114c1ec6
    path: ./declarative/manifests/heliocentric-model
    repoURL: http://165.22.209.118:3000/siddharth/gitops-argocd.git
  operationState:
    finishedAt: '2022-09-23T20:05:24Z'
    message: successfully synced (all tasks run)
    initiatedBy:
      automated: true
    retry:
      limit: 5
    sync:
      prune: true
      revision: e2edb3a016b752028c38adb898d34114c1ec6
      syncOptions:
        - CreateNamespace=true
    phase: Succeeded
    startedAt: '2022-09-23T20:05:21Z'
    syncResult:
      resources:
        - group: 
            hookPhase: Succeeded
            kind: Namespace
            message: namespace/heliocentric created
            namespace: heliocentric
            status: Synced
            syncPhase: PreSync
            version: v1
        - group: 
            hookPhase: Running
            kind: Service
            message: service/heliocentric-model-svc created
            name: heliocentric-model-svc
            namespace: heliocentric
            status: Sync

Review a consolidated list of applications on the dashboard:

The image shows a dashboard interface of an application management tool, displaying the health and sync status of various applications in a tree structure. The main application is "app-of-apps," and it is connected to other applications like "geocentric-app" and "heliocentric-app."

And a detailed list view of applications:

The image shows a dashboard interface of Argo CD, displaying a list of applications with their health and sync status, along with options to sync, refresh, or delete each application.

Accessing the Deployed Kubernetes Applications

Each sub-application deploys its own set of Kubernetes resources, including services that expose the applications. Below are the configuration details for these services.

Geocentric Model Service

The Geocentric model service represents an Earth-centered view and is configured as follows:

apiVersion: v1
kind: Service
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: >
      {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app.kubernetes.io/instance":"geocentric-app"},"name":"geocentric-model-svc","namespace":"geocentric"}}
  labels:
    app.kubernetes.io/instance: geocentric-app
  name: geocentric-model-svc

Heliocentric Model Service

The Heliocentric application uses a NodePort to expose its service:

apiVersion: v1
kind: Service
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: >
      {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app.kubernetes.io/instance":"heliocentric-app"},"name":"heliocentric-model-svc","namespace":"heliocentric"},"spec":{"clusterIP":"10.183.221.139","clusterIPs":["10.183.221.139"],"externalTrafficPolicy":"Cluster","internalTrafficPolicy":"Cluster","ipFamilies":["IPv4"],"ipFamilyPolicy":"SingleStack","ports":[{"nodePort":31334,"port":80,"protocol":"TCP","targetPort":80}],"selector":{"app":"heliocentric-model"},"sessionAffinity":"None","type":"NodePort"}}
spec:
  clusterIP: 10.183.221.139
  clusterIPs:
    - 10.183.221.139
  externalTrafficPolicy: Cluster
  internalTrafficPolicy: Cluster
  ipFamilies:
    - IPv4
  ipFamilyPolicy: SingleStack
  ports:
    - nodePort: 31334
      port: 80
      protocol: TCP
      targetPort: 80
  selector:
    app: heliocentric-model
  sessionAffinity: None
  type: NodePort
  loadBalancer: {}

Heliocentric Model Service (No Pluto)

For users who prefer an application variant that excludes Pluto, use the configuration below:

apiVersion: v1
kind: Service
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: >
      {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app.kubernetes.io/instance":"heliocentric-model-no-pluto-app"},"name":"heliocentric-model-no-pluto-svc","resourceVersion":"1964046","uid":"73603805-36c2-4296-bd9c-2f14cac42080"}}
spec:
  clusterIP: 10.180.97.241
  externalIPs:
    - 10.180.97.241
  externalTrafficPolicy: Cluster
  internalTrafficPolicy: Cluster
  ipFamily:
    - IPv4
  ipFamilyPolicy: SingleStack
  ports:
    - name: nodePort
      port: 80
      protocol: TCP
      targetPort: 80
  selector:
    app: heliocentric-model-no-pluto
  sessionAffinity: None
  type: NodePort
status:
  loadBalancer: {}

Many users advocate that Pluto should not be classified as a planet due to its distant orbit and retrograde rotation, which is why an application variant excluding Pluto is provided.

All these applications are deployed using a single ArgoCD app-of-apps configuration. This pattern not only simplifies management but also enables centralized control over multiple applications from a single Git repository and ArgoCD instance. For more detailed information on ArgoCD and GitOps, consider exploring the following resources:

Happy deploying!

Introduction

GitOps Introduction

ArgoCD Basics

ArgoCD Intermediate

ArgoCD Advanced/Admin

ArgoCD with Jenkins CI Pipeline

Declarative Setup App of Apps

Multi-App ArgoCD Application

App of Apps Configuration

Heliocentric App Manifest

Geocentric App Manifest

Kubernetes Application Manifests

Deployment Process

Viewing the Applications in the ArgoCD UI

Accessing the Deployed Kubernetes Applications

Geocentric Model Service

Heliocentric Model Service

Heliocentric Model Service (No Pluto)

Watch Video

​Multi-App ArgoCD Application

​App of Apps Configuration

​Heliocentric App Manifest

​Geocentric App Manifest

​Kubernetes Application Manifests

​Deployment Process

​Viewing the Applications in the ArgoCD UI

​Accessing the Deployed Kubernetes Applications

​Geocentric Model Service

​Heliocentric Model Service

​Heliocentric Model Service (No Pluto)

Watch Video

Multi-App ArgoCD Application

App of Apps Configuration

Heliocentric App Manifest

Geocentric App Manifest

Kubernetes Application Manifests

Deployment Process

Viewing the Applications in the ArgoCD UI

Accessing the Deployed Kubernetes Applications

Geocentric Model Service

Heliocentric Model Service

Heliocentric Model Service (No Pluto)