Maxwell MorrisandClaude Sonnet 5
92c3ad3191
A teaching-first, single-cluster GitOps setup: Talos Linux + Argo CD with an app-of-apps layout, MetalLB pre-installed for real LoadBalancer IPs on bare metal, a demo app, and a progressive docs/ walkthrough with a CLAUDE.md tutor persona and guided bootstrap checklist. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
120 lines
5.1 KiB
Markdown
120 lines
5.1 KiB
Markdown
# 04 — The app-of-apps pattern
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This is the last manual step. After this, Git drives everything.
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## The idea
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An Argo CD `Application` is a resource that says "watch this path in this
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Git repo, and keep the cluster matching what's there." The simplest
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possible setup is one Application per app you want to run — but then every
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new app means one more manual `kubectl apply`, which quietly puts you back
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to making changes by hand.
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**App-of-apps** fixes this by making Applications themselves something Argo
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CD manages. One Application — the app-of-apps — watches a folder
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([`apps/`](../apps)) full of *other* Application manifests. Add a new app by
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adding a new file to that folder and pushing it — the app-of-apps notices
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the new file and creates the Application it describes, which in turn
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deploys the app. No `kubectl apply` required past this point, ever, for a
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new app.
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```
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argocd/app-of-apps/app-of-apps.yaml (you apply this ONE file, by hand, once)
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│
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│ watches apps/, non-recursively
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├──────────────┬───────────────┐
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▼ ▼ ▼
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apps/demo.yaml apps/metallb.yaml (more, later — just add a file)
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│ │
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▼ ▼
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apps/demo/*.yaml apps/metallb/* (the actual manifests / Helm chart)
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```
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Three layers, each watching the next. You only ever touch the bottom two —
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the app-of-apps is set-and-forget. Notice `apps/metallb.yaml` is already
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here — see [`docs/05-metallb.md`](05-metallb.md) right after this one.
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## Why `apps/` isn't recursive
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Look at [`argocd/app-of-apps/app-of-apps.yaml`](../argocd/app-of-apps/app-of-apps.yaml)
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— specifically `directory.recurse: false`. The `apps/` folder contains both
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Application manifests (`apps/demo.yaml`, `apps/metallb.yaml`) *and*
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subfolders holding the real workload manifests those Applications point to
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(`apps/demo/*.yaml`, `apps/metallb/*`). Non-recursive means the
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app-of-apps only ever looks at files directly inside `apps/`, never inside
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its subfolders — so it only ever sees Application definitions, and leaves
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the actual workload manifests to the Application that owns them. Without
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this, the app-of-apps would try to apply raw Deployments and Helm chart
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files itself, duplicating and conflicting with what those Applications are
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already doing.
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## Every Application needs its own `repoURL`
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Applications don't inherit `repoURL` from whatever applied them — each one
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declares its own source repo independently. That means the placeholder
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`https://github.com/YOUR_GITHUB_USERNAME/...` needs fixing in *every* file
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that has it, not just the one you apply by hand:
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```sh
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grep -rl YOUR_GITHUB_USERNAME .
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```
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You should see three files: `argocd/app-of-apps/app-of-apps.yaml`,
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`apps/demo.yaml`, and `apps/metallb.yaml`. Edit `spec.source.repoURL` in
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each to point at your fork.
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## Steps
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1. Fix `repoURL` in all three files (above).
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2. Commit and push — this part matters more than it looks: the
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app-of-apps reads `apps/demo.yaml` and `apps/metallb.yaml` *from Git*,
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not from your local edits, so they have to be pushed before you apply
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anything.
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```sh
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git add argocd/app-of-apps/app-of-apps.yaml apps/demo.yaml apps/metallb.yaml
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git commit -m "Point Applications at my fork"
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git push
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```
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3. Apply the app-of-apps — the one manifest you apply by hand:
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```sh
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kubectl apply -f argocd/app-of-apps/app-of-apps.yaml
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```
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4. Watch it sync, then watch `demo` and `metallb` appear underneath it:
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```sh
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argocd app list
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```
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You should see `app-of-apps`, `demo`, and `metallb`, all `Synced` and
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`Healthy` within a minute or two (MetalLB's own install takes a little
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longer than the demo app).
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5. Confirm the demo app is actually running:
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```sh
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kubectl -n demo get pods,svc
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```
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You'll notice the Service's `EXTERNAL-IP` column says `<pending>` —
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that's expected. The demo app is a `LoadBalancer` Service, and nothing
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hands those out real addresses on bare metal until MetalLB is
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configured, which is exactly the next doc.
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If `app-of-apps`, `demo`, and `metallb` all show `Synced`/`Healthy`, the
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loop — Git → Argo CD → cluster — is already proven end to end; you just
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can't see the demo app in a browser yet.
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> **Ask Claude:** "walk me through exactly what happened, in order, from the
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> moment I ran `kubectl apply -f argocd/app-of-apps/app-of-apps.yaml` to
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> these three Applications existing." Making sure you can narrate that
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> chain yourself is the real checkpoint for this doc — everything from
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> here on is a variation on it.
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## Checklist
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- [ ] `repoURL` fixed in all three files listed above
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- [ ] Fix committed and pushed
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- [ ] `app-of-apps` applied and shows `Synced`/`Healthy`
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- [ ] `demo` and `metallb` Applications appeared automatically, both
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`Synced`/`Healthy`
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- [ ] `kubectl -n demo get pods,svc` shows the demo app's Pod running
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(Service `EXTERNAL-IP` still `<pending>` — expected for now)
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Continue to [`docs/05-metallb.md`](05-metallb.md) to give the demo app —
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and Argo CD's own UI — a real address.
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