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Argocd: ApplicationSet

Argocd: ApplicationSet
- ApplicationSet
- Common Commands

ApplicationSet

ApplicationSet
- a controller and CRD that automates the generation and management of multiple Argo CD Applications using a single, templated manifest.
- scales GitOps workflows by dynamically creating applications for numerous clusters, repositories, or environments (monorepos) without requiring a manual Application CRD for each one.
Use cases
- Use a single Kubernetes manifest to deploy into multiple Kubernetes clusters with Argo CD.
- Use a single Kubernetes manifest to deploy multiple applications from one or multiple Git repositories with Argo CD
How it works
- ApplicationSet controller:
  - only responsible of creating, updating and deleting application in ArgoCD namespace.
- ApplicationSet
  - not modify k8s resources.
  - Its Application controller responsibility to deploy resources into destination clusters.

Common Commands

Command	Description
`kubectl get appset -n argocd`	List ApplicationSets in the Argo CD namespace.
`kubectl get appset <name> -n argocd`	View one ApplicationSet.
`kubectl describe appset <name> -n argocd`	Show detailed status, events, and troubleshooting information.
`kubectl delete appset <name> -n argocd`	Delete an ApplicationSet. Usually also removes generated Applications.
`kubectl get applications -n argocd`	List Applications generated by the ApplicationSet.
`kubectl logs -n argocd deploy/argocd-applicationset-controller`	Check ApplicationSet controller logs.

Core Components

Template:
- A template of the standard Argo CD Application resource, containing placeholders like or .

Generator

Generator:
- Defines how to fill the template (e.g., pulling cluster names from ArgoCD secrets or directories from Git).
- responsible for dynamically creating application parameters, driving automation to deploy apps across multiple clusters or repositories.
Types of generators
- List generator
- Cluster generator
- Git generator
- Matrix generator
- Merge generator
- SCM provider generator
- Pull request generator
- Cluster Decision Resource generator

List generator

List generator:
- allows to target Argo CD Applications to clusters based on a fixed list of cluster name/URL values.
- any key/value element pair is supported.
- Clusters need to be pre-defined in ArgoCD.
Example

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: guestbook
spec:
  generators:
    - list:
      elements:
        - cluster: engineering-prod-1
          url: https://1.2.3.4
        - cluster: engineering-prod-2
          url: https://2.4.6.8
template:
  metadata:
    name: "-guestbook"
  spec:
    destination:
      server: ""
      namespace: guestbook
    source:
      repoURL: https://github.com/argoproj/argocd-example-apps.git
      targetRevision: HEAD
      path: guestbook/

Cluster Generator

The Cluster generator allows you to generate applications based on the list of clusters defined within Argo CD
The following parameter values to the Application template for each cluster:
- name
- nameNormalized (‘name’ but normalized to contain only lowercase alphanumeric characters, ‘-‘ or ‘.’)
- server
- metadata.labels. (for each label in the Secret)
- metadata.annotations. (for each annotation in the Secret)
Additional key/value pairs can be set manually via values field.
Example

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: guestbook
spec:
  generators:
    - cluster:
        selector: # the cluater with target labels
          matchLabels:
            env: staging
        values: # additional values
          revision: HEAD
    - cluster:
        selector: # the cluater with target labels
          matchLabels:
            env: production
        values: # additional values
          revision: stable

  template:
    metadata:
      name: "-guestbook"
    spec:
      destination:
        server: ""
        namespace: guestbook
      source:
        repoURL: https://github.com/argoproj/argocd-example-apps.git
        targetRevision: ""
        path: guestbook

Git Generator

Git generator:
- generates parameters based on files or folders that are contained within the Git repository defined within the applicationset resource.
Contains two subtypes:
- Git directory generator:
  - generates parameters using the directory structure of a specified Git repository.
- Git file generator:
  - generates parameters using the contents of JSON/YAML files found within a specified repository.

parameters are:

``: The directory paths within the Git repository that match the path wildcard.
``: For any directory path within the Git repository that matches the path wildcard, the right-most path name is extracted (e.g. /directory/directory2 would produce directory2).
``: This field is the same as path.basename with unsupported characters replaced with - (e.g. a path of /directory/directory_2, and path.basename of directory_2 would produce directory-2 here).

exclude feature

The Git directory generator will automatically exclude folders that begin with . (such as .git).
The Git directory generator also supports an exclude option in order to exclude directories.

Matrix generator: The Matrix generator may be used to combine the generated parameters of two separate generators. • Merge generator: The Merge generator may be used to merge the generated parameters of two or more generators. Additional generators can override the values of the base generator. • SCM Provider generator: The SCM Provider generator uses the API of an SCM provider (eg GitHub) to automatically discover repositories within an organization. • Pull Request generator: The Pull Request generator uses the API of an SCMaaS provider (eg GitHub) to automatically discover open pull requests within an repository. • Cluster Decision Resource generator: The Cluster Decision Resource generator is used to interface with Kubernetes custom resources that use custom resourcespecific logic to decide which set of Argo CD clusters to deploy to.

Lab: Deploy Applications with ApplicationSet

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet

metadata:
  name: guestbook-appset
  namespace: argocd

spec:
  goTemplate: true
  goTemplateOptions:
    - missingkey=error

  generators:
    - list:
        elements:
          - env: dev
            namespace: guestbook-dev
          - env: prod
            namespace: guestbook-prod

  template:
    metadata:
      name: "-guestbook"

    spec:
      project: default

      source:
        repoURL: https://github.com/argoproj/argocd-example-apps.git
        targetRevision: HEAD
        path: guestbook

      destination:
        server: https://kubernetes.default.svc
        namespace: ""

      syncPolicy:
        syncOptions:
          - CreateNamespace=true

kubectl apply -f demo_appset.yaml
# applicationset.argoproj.io/guestbook-appset created

argocd app sync dev-guestbook
argocd app sync prod-guestbook

argocd app list
# NAME                   CLUSTER                         NAMESPACE       PROJECT  STATUS  HEALTH   SYNCPOLICY  CONDITIONS  REPO                                                 PATH       TARGET
# argocd/dev-guestbook   https://kubernetes.default.svc  guestbook-dev   default  Synced  Healthy  Manual      <none>      https://github.com/argoproj/argocd-example-apps.git  guestbook  HEAD
# argocd/prod-guestbook  https://kubernetes.default.svc  guestbook-prod  default  Synced  Healthy  Manual      <none>      https://github.com/argoproj/argocd-example-apps.git  guestbook  HEAD