Applications in ArgoCD can be created by the UI, CLI, or by applying a manifest file in Kubernetes (declarative setup, mono application). Mono application is where an application is exported or written as a manifest file with the type of Application

App of apps

A pattern of deploying and managing a group of applications using a single top-level ArgoCD application which manages multiple mono applications then the mono applications execute the manifest files each with its own Git repository and path

Multiple interdependent applications, each with its own unique requirements and deployment process. Any changes made to the top level will trigger to all of the managed applications

Say the following example has the app-of-apps.yaml file the top level which executes the app1.yaml and app2.yaml mono apps, the mono apps then execute each of the targeted manifest files accordingly. It doesn’t has to be in the same repository or the same structure

Folder structure

Example
├───app-of-apps
│       app1.yaml
│       app2.yaml
├───manifests
│   ├───app1
│   │       deployment.yaml
│   │       service.yaml
│   └───app2
│           deployment.yaml
│           service.yaml
└───top-level
        app-of-apps.yaml

Top level file

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: app-of-apps
  namespace: argocd
spec:
  project: default
  source:
    repoURL: <Git_URL>
    targetRevision: HEAD
    # where the mono apps are located
    path: <./path/to/manifest>
  destination:
    server: <https://kubernetes.default.svc>
    namespace: argocd
  syncPolicy:
    automated:
      prune: true
      selfHeal: true

Mono app file

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: app1
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io
spec:
  project: default
  source:
    repoURL: <Git_URL>
    targetRevision: HEAD
    # where the manifest files (svc, deployment, etc..) are stored
    path: <./path/to/manifest>   
  destination:
    server: <https://kubernetes.default.svc>
    namespace: app1_ns
  syncPolicy:
    syncOptions:
      - CreateNamespace=true  
    automated:
      prune: true
      selfHeal: true

The top level file can be applied directly from the Git repo

kubectl apply -f <git_Repo_with_path_to_file_URL> -n argocd

# check applications created in kubernetes
kubectl get Application -n argocd # or -A

Helm charts

ArgoCD can be used to deploy Helm charts, can also automatically detect values of a chart and change it while creating an application

Alternatively can use command line to create the application and change values accordingly

argocd app create <helm_app_name> \\
--repo <Helm_repo_URL> \\
--path <./path> \\
--helm-set service.type=NodePort \\
--helm-set <paramater>.<key>=<value> \\
--dest-namespace default \\
--dest-server <https://kubernetes.default.svc>

Note: if you try to list installed helm charts using helm ls there will be no output because its a created application not a created chart