# cluster-autoscaler-with-capi

Node autoscaling for Kubernetes clusters running as VMs on a home-lab hypervisor fleet
(Proxmox VE + vanilla KVM/libvirt), driven by **Cluster API** and **cluster-autoscaler** —
growing, in later phases, into a "poor man's Kubernetes-as-a-Service".

> Status: **Phase 1 in progress** — VM template built and smoke-tested; management cluster
> running (k3s + CAPI via cluster-api-operator, built by [ansible/mgmt.yml](ansible/mgmt.yml));
> first workload cluster `lab1` next. Versions verified 2026-09-24/26/27, see [docs/versions.md](docs/versions.md).

## Goals

- Workload clusters whose worker pool scales **0 → N → 0** on demand, with VMs created and
  destroyed on the hypervisors automatically.
- Everything declarative: clusters are CAPI objects in a management cluster; no hand-made VMs.
- Learn Cluster API internals (contracts, providers, reconcile flow) by assembling, then extending it.
- End state: self-service tenant clusters (hosted control planes + autoscaled VM workers).

## Non-goals (for now)

- HA management cluster, production SLAs, multi-site.
- GitOps / fleet management (may come later on top).
- Writing our own autoscaler — cluster-autoscaler's `clusterapi` provider does the job.

## Lab inventory

| Hypervisor type | Management API | CAPI infrastructure provider |
| --- | --- | --- |
| Proxmox VE (e.g. `pv1-1`, 192.168.0.8) | PVE REST API :8006 | CAPMOX (phase 1) |
| Ubuntu 24.04 + KVM/libvirt | libvirt RPC (`qemu+ssh`/`qemu+tls`) | none mature upstream → phase 2 |

VM network: `vmbr0` (VLAN-aware), VLAN 4, build host 192.168.4.181.

## Architecture (phase 1)

```mermaid
flowchart LR
  subgraph MGMT[mgmt cluster: k3s VM]
    CAPI[CAPI core + kubeadm bootstrap/CP]
    CAPMOX[CAPMOX]
    IPAM[IPAM in-cluster]
    CA[cluster-autoscaler]
  end
  PVE[Proxmox VE API]
  subgraph LAB1[workload cluster lab1]
    CP[control plane VM + kube-vip VIP]
    W[worker VMs - MachineDeployment 0..N]
  end
  CA -- scales MachineDeployment --> CAPI
  CAPI --> CAPMOX
  CAPMOX -- clone template, cloud-init ISO --> PVE
  PVE --> CP
  PVE --> W
  CA -- watches pending pods via lab1-kubeconfig --> LAB1
```

cluster-autoscaler runs in the management cluster in `kubeconfig-incluster` mode: it reads
pending pods/nodes from the workload cluster through the CAPI-generated kubeconfig secret and
changes `replicas` on MachineDeployments via the in-cluster management API.

## Roadmap

| Phase | Scope | Exit criteria | Doc |
| --- | --- | --- | --- |
| **1** | k3s mgmt cluster (manual) → CAPI + CAPMOX → workload cluster on Proxmox VMs → cluster-autoscaler | scale-up 1→3, scale-down to 0, scale-from-zero all work | [phase-1-proxmox-capi.md](docs/phase-1-proxmox-capi.md) |
| **2** | CAPI provider for vanilla KVM/libvirt hosts (evaluate CAPLV / KubeVirt / Metal3 / own provider) | worker MachineDeployment on Ubuntu KVM hosts, autoscaled | [phase-2-kvm-provider.md](docs/phase-2-kvm-provider.md) |
| **3** | Hosted control planes with Kamaji, tenant clusters on demand ("poor man's KaaS") | new tenant cluster from one manifest/ClusterClass, workers autoscaled | [phase-3-kamaji-kaas.md](docs/phase-3-kamaji-kaas.md) |

Phases 2 and 3 are independent and can be done in either order.

## Repository layout

```
.
├── README.md                     # this file
├── CLAUDE.md                     # context + rules for Claude Code sessions
├── CHANGELOG.md                  # milestones and significant changes, newest first
├── ansible/                      # mgmt.yml: management VM + k3s + cert-manager + CAPI operator/providers
├── .claude/
│   ├── agents/                   # upstream-researcher, cluster-inspector (read-only)
│   ├── commands/                 # /ship
│   └── cluster-inspector/        # RBAC, kubeconfig minting script, gitignored kubeconfigs/
├── docs/
│   ├── decisions.md              # decision log: alternatives, why, status
│   ├── future-tasks.md           # deferred work with context, newest first
│   ├── plans/                    # plans (plan mode), one file per plan
│   ├── plans-executions/         # per-plan execution logs with exact commands
│   ├── sessions/                 # research/design conversation summaries
│   ├── prompts/                  # prompts/specs that kicked off work
│   ├── reviews/                  # review findings
│   ├── versions.md               # pinned versions + compatibility reasoning
│   ├── phase-1-proxmox-capi.md   # runbook for phase 1
│   ├── image-builder-proxmox.md  # building the node VM template + fixes log
│   ├── phase-2-kvm-provider.md   # KVM/libvirt provider options
│   └── phase-3-kamaji-kaas.md    # hosted control planes / KaaS design notes
└── configs/
    ├── image-builder/            # packer var file for the Proxmox template
    ├── capi/                     # clusterctl config example
    ├── cluster-autoscaler/       # Helm values
    └── test/                     # workloads for scale tests
```

Secrets (PVE token secret, kubeconfigs) never go into the repo — see `.gitignore`.

## Key decisions so far

Short summary; the full log with alternatives and status is [docs/decisions.md](docs/decisions.md).

1. **CAPI v1.12.x, not the latest 1.14.x** — CAPMOX v0.9.x is only tested against CAPI 1.11/1.12.
   This caps workload Kubernetes at **1.35** and cluster-autoscaler at **1.35.x**.
2. **Management cluster = k3s on a Proxmox VM**, not kind — CAPI controllers and the autoscaler
   must run permanently.
3. **Node images via kubernetes-sigs/image-builder** (Ubuntu 24.04, Proxmox builder), overrides in
   a `PACKER_VAR_FILES` JSON instead of `PACKER_FLAGS`.
4. **CNI installed by Helm** (Cilium, `ipam.mode=kubernetes`), not via ClusterResourceSet flavors,
   to keep its version under our control.
5. **Scale-from-zero via capacity annotations** on the MachineDeployment — CAPMOX does not publish
   `status.capacity` on `ProxmoxMachineTemplate`.
6. **Management cluster from one idempotent Ansible playbook**, CAPI providers installed by
   **cluster-api-operator** instead of `clusterctl init` — re-runs are no-ops, upgrades are version bumps.