k8s-starter-pack/docs/04-app-of-apps.md

# 04 — The app-of-apps pattern

This is the last manual step. After this, Git drives everything.

## The idea

An Argo CD `Application` is a resource that says "watch this path in this
Git repo, and keep the cluster matching what's there." The simplest
possible setup is one Application per app you want to run — but then every
new app means one more manual `kubectl apply`, which quietly puts you back
to making changes by hand.

**App-of-apps** fixes this by making Applications themselves something Argo
CD manages. One Application — the app-of-apps — watches a folder
([`apps/`](../apps)) full of *other* Application manifests. Add a new app by
adding a new file to that folder and pushing it — the app-of-apps notices
the new file and creates the Application it describes, which in turn
deploys the app. No `kubectl apply` required past this point, ever, for a
new app.

```
argocd/app-of-apps/app-of-apps.yaml   (you apply this ONE file, by hand, once)
        │
        │  watches apps/, non-recursively
        ├──────────────┬───────────────┐
        ▼               ▼               ▼
   apps/demo.yaml   apps/metallb.yaml   (more, later — just add a file)
        │               │
        ▼               ▼
   apps/demo/*.yaml  apps/metallb/*    (the actual manifests / Helm chart)
```

Three layers, each watching the next. You only ever touch the bottom two —
the app-of-apps is set-and-forget. Notice `apps/metallb.yaml` is already
here — see [`docs/05-metallb.md`](05-metallb.md) right after this one.

## Why `apps/` isn't recursive

Look at [`argocd/app-of-apps/app-of-apps.yaml`](../argocd/app-of-apps/app-of-apps.yaml)
— specifically `directory.recurse: false`. The `apps/` folder contains both
Application manifests (`apps/demo.yaml`, `apps/metallb.yaml`) *and*
subfolders holding the real workload manifests those Applications point to
(`apps/demo/*.yaml`, `apps/metallb/*`). Non-recursive means the
app-of-apps only ever looks at files directly inside `apps/`, never inside
its subfolders — so it only ever sees Application definitions, and leaves
the actual workload manifests to the Application that owns them. Without
this, the app-of-apps would try to apply raw Deployments and Helm chart
files itself, duplicating and conflicting with what those Applications are
already doing.

## Every Application needs its own `repoURL`

Applications don't inherit `repoURL` from whatever applied them — each one
declares its own source repo independently. That means the placeholder
`https://github.com/YOUR_GITHUB_USERNAME/...` needs fixing in *every* file
that has it, not just the one you apply by hand:

```sh
grep -rl YOUR_GITHUB_USERNAME .
```

You should see three files: `argocd/app-of-apps/app-of-apps.yaml`,
`apps/demo.yaml`, and `apps/metallb.yaml`. Edit `spec.source.repoURL` in
each to point at your fork.

## Steps

1. Fix `repoURL` in all three files (above).
2. Commit and push — this part matters more than it looks: the
   app-of-apps reads `apps/demo.yaml` and `apps/metallb.yaml` *from Git*,
   not from your local edits, so they have to be pushed before you apply
   anything.
   ```sh
   git add argocd/app-of-apps/app-of-apps.yaml apps/demo.yaml apps/metallb.yaml
   git commit -m "Point Applications at my fork"
   git push
   ```
3. Apply the app-of-apps — the one manifest you apply by hand:
   ```sh
   kubectl apply -f argocd/app-of-apps/app-of-apps.yaml
   ```
4. Watch it sync, then watch `demo` and `metallb` appear underneath it:
   ```sh
   argocd app list
   ```
   You should see `app-of-apps`, `demo`, and `metallb`, all `Synced` and
   `Healthy` within a minute or two (MetalLB's own install takes a little
   longer than the demo app).
5. Confirm the demo app is actually running:
   ```sh
   kubectl -n demo get pods,svc
   ```
   You'll notice the Service's `EXTERNAL-IP` column says `<pending>` —
   that's expected. The demo app is a `LoadBalancer` Service, and nothing
   hands those out real addresses on bare metal until MetalLB is
   configured, which is exactly the next doc.

If `app-of-apps`, `demo`, and `metallb` all show `Synced`/`Healthy`, the
loop — Git → Argo CD → cluster — is already proven end to end; you just
can't see the demo app in a browser yet.

> **Ask Claude:** "walk me through exactly what happened, in order, from the
> moment I ran `kubectl apply -f argocd/app-of-apps/app-of-apps.yaml` to
> these three Applications existing." Making sure you can narrate that
> chain yourself is the real checkpoint for this doc — everything from
> here on is a variation on it.

## Checklist

- [ ] `repoURL` fixed in all three files listed above
- [ ] Fix committed and pushed
- [ ] `app-of-apps` applied and shows `Synced`/`Healthy`
- [ ] `demo` and `metallb` Applications appeared automatically, both
      `Synced`/`Healthy`
- [ ] `kubectl -n demo get pods,svc` shows the demo app's Pod running
      (Service `EXTERNAL-IP` still `<pending>` — expected for now)

Continue to [`docs/05-metallb.md`](05-metallb.md) to give the demo app —
and Argo CD's own UI — a real address.