🤖 feat: add Argo CD single-apply ApplicationSet example (#75)

## Summary
Add a new Argo CD example that lets users bootstrap CloudNativePG +
coder-k8s + PostgreSQL + `CoderControlPlane` from a single
`ApplicationSet` manifest.

## Background
The repository already had a manual CloudNativePG example, but GitOps
users had to perform several separate install steps. This change adds a
one-apply Argo CD flow aligned with that example so evaluator clusters
can stand up quickly.

## Implementation
- Added `examples/argocd/` with:
  - `applicationset.yaml` (single resource to apply)
  - child Applications for:
    - CloudNativePG operator (Helm source)
- coder-k8s operator stack (`config/crd/bases`, `config/rbac`, `deploy`)
    - CloudNativePG-backed Coder resources (`examples/cloudnativepg`)
- Added sync-wave ordering between child Applications (`wave 0`
operators, `wave 1` app resources).
- Added resource-level Argo sync-wave annotations in
`examples/cloudnativepg/`:
  - namespace `wave 0`
  - CNPG `Cluster` `wave 1`
  - `CoderControlPlane` `wave 2`
- Updated README docs:
  - top-level `README.md` examples list now includes `examples/argocd/`
- `examples/cloudnativepg/README.md` now documents shared Argo sync-wave
behavior

## Validation
- `make verify-vendor`
- `make test`
- `make build`
- `make lint`
- `make docs-check`
- Parsed changed YAML files with `yaml.safe_load_all` to verify syntax.

## Risks
- The example references `targetRevision: main` for repository-backed
Applications, which is intentionally convenient for demos but not pinned
for reproducible production installs.
- The CloudNativePG chart target revision remains flexible by default;
users should pin versions for stricter reproducibility.

---

_Generated with [`mux`](https://github.com/coder/mux) • Model:
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Author: ThomasK33

README.md

@@ -74,6 +74,7 @@ make docs-serve
 ## Examples
 
 - [`examples/cloudnativepg/`](examples/cloudnativepg/) — Deploy a `CoderControlPlane` with a CloudNativePG-managed PostgreSQL backend.
+- [`examples/argocd/`](examples/argocd/) — Bootstrap CloudNativePG + `coder-k8s` + PostgreSQL + `CoderControlPlane` from one Argo CD `ApplicationSet`.
 
 - [`examples/aggregated/`](examples/aggregated/) - Reusable `CoderTemplate` manifests for aggregated API testing.
 

examples/argocd/README.md

@@ -0,0 +1,70 @@
+# Argo CD single-apply example (CloudNativePG + coder-k8s)
+
+This example bootstraps the full stack from one `ApplicationSet`.
+
+The generated Argo CD `Application` uses multiple sources to deploy:
+
+1. CloudNativePG operator (Helm chart)
+2. `coder-k8s` operator stack (`config/crd/bases`, `config/rbac`, `deploy`)
+3. CloudNativePG PostgreSQL `Cluster`
+4. `CoderControlPlane`
+
+## Prerequisites
+
+- A Kubernetes cluster
+- `kubectl` configured for that cluster
+- Argo CD installed (including the ApplicationSet controller)
+- Argo CD v2.6+ (required for `spec.sources` in the generated Application)
+
+## Apply one manifest
+
+```bash
+kubectl apply -f examples/argocd/applicationset.yaml
+```
+
+That creates:
+
+- `ApplicationSet` `coder-k8s-stack`
+- generated `Application` `coder-k8s-stack`
+
+## Ordering behavior
+
+This setup avoids app-of-apps ordering ambiguity by using a single generated `Application` with multiple sources.
+
+Resource-level sync waves provide dependency ordering for workload resources:
+
+- `examples/argocd/resources/00-coder-system-namespace.yaml` uses `wave -1`
+- `examples/cloudnativepg/00-namespace.yaml` uses `wave 0`
+- `examples/cloudnativepg/cnpg-cluster.yaml` uses `wave 1`
+- `examples/cloudnativepg/codercontrolplane.yaml` uses `wave 2`
+
+## Watch rollout
+
+```bash
+kubectl -n argocd get applications
+kubectl -n coder wait --for=condition=Ready cluster/coder-db --timeout=10m
+kubectl -n coder rollout status deployment/coder --timeout=10m
+```
+
+## Access Coder
+
+```bash
+kubectl -n coder port-forward svc/coder 3000:80
+```
+
+Open <http://localhost:3000/setup> and complete the setup flow.
+
+## Customization
+
+- This example tracks `https://github.com/coder/coder-k8s.git` at `main`.
+  Update `repoURL` and `targetRevision` in `examples/argocd/applicationset.yaml` if you want to pin to a tag or use a fork.
+- The CloudNativePG chart version is configurable with `cloudnativepgChartVersion`.
+  Pin it to an explicit chart version for reproducible environments.
+
+## Cleanup
+
+```bash
+kubectl -n argocd delete applicationset coder-k8s-stack
+```
+
+The generated `Application` includes `resources-finalizer.argocd.argoproj.io` so deleting the `ApplicationSet` cascades cleanup of managed resources. Depending on your storage class reclaim policy, PVCs from PostgreSQL may remain after cleanup.

examples/argocd/applicationset.yaml

@@ -0,0 +1,60 @@
+apiVersion: argoproj.io/v1alpha1
+kind: ApplicationSet
+metadata:
+  name: coder-k8s-stack
+  namespace: argocd
+  labels:
+    app.kubernetes.io/part-of: coder-k8s-example
+spec:
+  goTemplate: true
+  goTemplateOptions:
+    - missingkey=error
+  generators:
+    - list:
+        elements:
+          - name: coder-k8s-stack
+            destinationServer: https://kubernetes.default.svc
+            destinationNamespace: cnpg-system
+            repoURL: https://github.com/coder/coder-k8s.git
+            targetRevision: main
+            cloudnativepgChartVersion: "*"
+  template:
+    metadata:
+      name: "{{ .name }}"
+      namespace: argocd
+      finalizers:
+        - resources-finalizer.argocd.argoproj.io
+      labels:
+        app.kubernetes.io/part-of: coder-k8s-example
+    spec:
+      project: default
+      sources:
+        - repoURL: https://cloudnative-pg.github.io/charts
+          chart: cloudnative-pg
+          targetRevision: "{{ .cloudnativepgChartVersion }}"
+          helm:
+            releaseName: cnpg
+        - repoURL: "{{ .repoURL }}"
+          targetRevision: "{{ .targetRevision }}"
+          path: examples/argocd/resources
+        - repoURL: "{{ .repoURL }}"
+          targetRevision: "{{ .targetRevision }}"
+          path: config/crd/bases
+        - repoURL: "{{ .repoURL }}"
+          targetRevision: "{{ .targetRevision }}"
+          path: config/rbac
+        - repoURL: "{{ .repoURL }}"
+          targetRevision: "{{ .targetRevision }}"
+          path: deploy
+        - repoURL: "{{ .repoURL }}"
+          targetRevision: "{{ .targetRevision }}"
+          path: examples/cloudnativepg
+      destination:
+        server: "{{ .destinationServer }}"
+        namespace: "{{ .destinationNamespace }}"
+      syncPolicy:
+        automated:
+          prune: true
+          selfHeal: true
+        syncOptions:
+          - CreateNamespace=true

examples/argocd/resources/00-coder-system-namespace.yaml

@@ -0,0 +1,8 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: coder-system
+  annotations:
+    argocd.argoproj.io/sync-wave: "-1"
+  labels:
+    app.kubernetes.io/part-of: coder-k8s-example

examples/cloudnativepg/00-namespace.yaml

@@ -2,5 +2,7 @@ apiVersion: v1
 kind: Namespace
 metadata:
   name: coder
+  annotations:
+    argocd.argoproj.io/sync-wave: "0"
   labels:
     app.kubernetes.io/part-of: coder-k8s-example

examples/cloudnativepg/README.md

@@ -46,6 +46,8 @@ kubectl apply -f examples/cloudnativepg/
 
 The namespace manifest is prefixed (`00-namespace.yaml`) so `kubectl apply -f` creates `coder` before namespaced resources.
 
+These manifests also include Argo CD sync-wave annotations so the same directory works with [`examples/argocd/`](../argocd/): namespace (`wave 0`) -> CloudNativePG `Cluster` (`wave 1`) -> `CoderControlPlane` (`wave 2`).
+
 Wait for PostgreSQL and verify the generated Secret:
 
 ```bash

examples/cloudnativepg/cnpg-cluster.yaml

@@ -3,6 +3,9 @@ kind: Cluster
 metadata:
   name: coder-db
   namespace: coder
+  annotations:
+    argocd.argoproj.io/sync-wave: "1"
+    argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true
 spec:
   instances: 1
   storage:

examples/cloudnativepg/codercontrolplane.yaml

@@ -3,6 +3,9 @@ kind: CoderControlPlane
 metadata:
   name: coder
   namespace: coder
+  annotations:
+    argocd.argoproj.io/sync-wave: "2"
+    argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true
 spec:
   replicas: 1
   service: