auto-apps

As of today, there is no formal support for the app of apps pattern, and the ArgoCD ecosystem lacks a construct where Applications can inherit easily from other Applications.

auto-apps is a stupid simple cli intended to bridge the gap until ApplicationSets are officially supported in ArgoCD. It is designed to fill a gap in the ArgoCD app of apps pattern, where multiple applications are bootstrapped from a single "umbrella" application.

Features

Application auto discovery

Starting from a given spec.source.path, autoapps will traverse a git repository looking for:

• valid *.yaml or *.yml
• manifests of type: argoproj.io/v1alpha1 and kind: Application
• manifests with an annotation present of autoapps

Simple Application templating

Using custom argocd tooling, Applications can utilize the spec.source.plugin spec to template child groups of Applications.

autoapps uses fasttemplate to perform its substitution. Since ArgoCD currently only supports specifying environment variables within plugins, autoapps accepts two forms of substitution:

AUTOAPPS_ prefixed:

Variables prefixed with AUTOAPPS_ are valid candidates for templating, and will have their prefix stripped before templating. For example:

# Parent Application
...
spec:
  source:
    plugin:
      name: autoapps
      env:
      - name: AUTOAPPS_foo
        value: bar
...

# Child Application
...
spec:
  source:
    path: {{foo}}
...

Identifying valid variables for templating via AUTOAPPS_ prefix protects abuse against using protected or private system environment variables as template values. However, one of the restrictions of this means you're limited to valid environment variable names.

Builtin ArgoCD variables:

ArgoCD uses a couple builtin environment variables at runtime that are useful:

# Parent Application
...
spec:
  source:
    plugin:
      name: autoapps
...

# Child Application
...
spec:
  source:
    targetRevision: {{ARGOCD_APP_SOURCE_TARGET_REVISION}}
...

Examples

Consider the following app of apps structure:

# Application A syncs Application B and C, which subsequently deploy manifests
          +---+
          | B | --> App B Manifests
+---+     +---+
| A | --> 
+---+     +---+
          | C | --> App C Manifests
          +---+

If you want B and C to dynamically inherit values completely encapsulated within A's manifests:

The "umbrella" application:

# Application A CRD (umbrella app)
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: umbrella
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io
spec:
  project: core

  source:
    repoURL: https://github.com/joshrwolf/core-bootstrap
    targetRevision: HEAD
    path: "."   # Leverage `autoapps` traversal discovery

    plugin:
      env:
      - name: FOO
        value: bar

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

The subsequent "child" application

# Application B CRD (child app)
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: mocha
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io
  annotations:
    argocd.argoproj.io/sync-wave: "1"
spec:
  project: {{ARGOCD_PROJECT}}

  source:
    repoURL: {{project_repo}}
    targetRevision: {{ARGOCD_APP_SOURCE_TARGET_REVISION}}    # leverage standard build environment variables
    path: apps/istio

  destination:
    server: https://kubernetes.default.svc
    namespace: istio-system

While the above is doable with any of the other templating tools, autoapps keeps the configuration entirely within the Application CRD, enables runtime configuration, and simplifies "glue" templating with auto discovery of Applications.

Dynamically skipping/ignoring applications

autoapps will skip any applications which are annotated as follows:

# NOTE: Portions of the complete spec are skipped below for brevity
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: mocha
  annotations:
    autoapps-skip-discovery: "true"
...

To make this dynamic, you can leverage variable substitution from the parent application as follows:

# Parent Application
...
spec:
  source:
    plugin:
      name: autoapps
      env:
      - name: AUTOAPPS_skip_mocha
        value: "true"
...

# Child Application
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: mocha
  annotations:
    autoapps-skip-discovery: "{{skip_mocha}}"
...