kacerrandClaude Opus 5.5
5fd998c5f9
Phase 1-3 runbooks and design notes, version pins, config templates, project-history conventions, cluster-inspector read-only credentials setup. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
116 lines
5.7 KiB
Markdown
116 lines
5.7 KiB
Markdown
# cluster-autoscaler-with-capi
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Node autoscaling for Kubernetes clusters running as VMs on a home-lab hypervisor fleet
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(Proxmox VE + vanilla KVM/libvirt), driven by **Cluster API** and **cluster-autoscaler** —
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growing, in later phases, into a "poor man's Kubernetes-as-a-Service".
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> Status: **Phase 1 in progress** — VM template built and smoke-tested; management cluster
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> and first workload cluster next. Versions verified 2026-09-24/26, see [docs/versions.md](docs/versions.md).
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## Goals
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- Workload clusters whose worker pool scales **0 → N → 0** on demand, with VMs created and
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destroyed on the hypervisors automatically.
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- Everything declarative: clusters are CAPI objects in a management cluster; no hand-made VMs.
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- Learn Cluster API internals (contracts, providers, reconcile flow) by assembling, then extending it.
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- End state: self-service tenant clusters (hosted control planes + autoscaled VM workers).
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## Non-goals (for now)
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- HA management cluster, production SLAs, multi-site.
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- GitOps / fleet management (may come later on top).
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- Writing our own autoscaler — cluster-autoscaler's `clusterapi` provider does the job.
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## Lab inventory
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| Hypervisor type | Management API | CAPI infrastructure provider |
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| --- | --- | --- |
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| Proxmox VE (e.g. `pv1-1`, 192.168.0.8) | PVE REST API :8006 | CAPMOX (phase 1) |
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| Ubuntu 24.04 + KVM/libvirt | libvirt RPC (`qemu+ssh`/`qemu+tls`) | none mature upstream → phase 2 |
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VM network: `vmbr0` (VLAN-aware), VLAN 4, build host 192.168.4.181.
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## Architecture (phase 1)
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```mermaid
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flowchart LR
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subgraph MGMT[mgmt cluster: k3s VM]
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CAPI[CAPI core + kubeadm bootstrap/CP]
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CAPMOX[CAPMOX]
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IPAM[IPAM in-cluster]
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CA[cluster-autoscaler]
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end
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PVE[Proxmox VE API]
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subgraph LAB1[workload cluster lab1]
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CP[control plane VM + kube-vip VIP]
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W[worker VMs - MachineDeployment 0..N]
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end
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CA -- scales MachineDeployment --> CAPI
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CAPI --> CAPMOX
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CAPMOX -- clone template, cloud-init ISO --> PVE
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PVE --> CP
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PVE --> W
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CA -- watches pending pods via lab1-kubeconfig --> LAB1
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```
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cluster-autoscaler runs in the management cluster in `kubeconfig-incluster` mode: it reads
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pending pods/nodes from the workload cluster through the CAPI-generated kubeconfig secret and
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changes `replicas` on MachineDeployments via the in-cluster management API.
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## Roadmap
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| Phase | Scope | Exit criteria | Doc |
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| --- | --- | --- | --- |
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| **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) |
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| **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) |
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| **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) |
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Phases 2 and 3 are independent and can be done in either order.
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## Repository layout
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```
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.
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├── README.md # this file
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├── CLAUDE.md # context + rules for Claude Code sessions
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├── CHANGELOG.md # milestones and significant changes, newest first
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├── .claude/
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│ ├── agents/ # upstream-researcher, cluster-inspector (read-only)
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│ ├── commands/ # /ship
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│ └── cluster-inspector/ # RBAC, kubeconfig minting script, gitignored kubeconfigs/
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├── docs/
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│ ├── decisions.md # decision log: alternatives, why, status
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│ ├── plans/ # plans (plan mode), one file per plan
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│ ├── plans-executions/ # per-plan execution logs with exact commands
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│ ├── sessions/ # research/design conversation summaries
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│ ├── prompts/ # prompts/specs that kicked off work
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│ ├── reviews/ # review findings
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│ ├── versions.md # pinned versions + compatibility reasoning
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│ ├── phase-1-proxmox-capi.md # runbook for phase 1
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│ ├── image-builder-proxmox.md # building the node VM template + fixes log
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│ ├── phase-2-kvm-provider.md # KVM/libvirt provider options
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│ └── phase-3-kamaji-kaas.md # hosted control planes / KaaS design notes
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└── configs/
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├── image-builder/ # packer var file for the Proxmox template
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├── capi/ # clusterctl config example
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├── cluster-autoscaler/ # Helm values
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└── test/ # workloads for scale tests
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```
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Secrets (PVE token secret, kubeconfigs) never go into the repo — see `.gitignore`.
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## Key decisions so far
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Short summary; the full log with alternatives and status is [docs/decisions.md](docs/decisions.md).
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1. **CAPI v1.12.x, not the latest 1.14.x** — CAPMOX v0.9.x is only tested against CAPI 1.11/1.12.
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This caps workload Kubernetes at **1.35** and cluster-autoscaler at **1.35.x**.
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2. **Management cluster = k3s on a Proxmox VM**, not kind — CAPI controllers and the autoscaler
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must run permanently.
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3. **Node images via kubernetes-sigs/image-builder** (Ubuntu 24.04, Proxmox builder), overrides in
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a `PACKER_VAR_FILES` JSON instead of `PACKER_FLAGS`.
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4. **CNI installed by Helm** (Cilium, `ipam.mode=kubernetes`), not via ClusterResourceSet flavors,
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to keep its version under our control.
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5. **Scale-from-zero via capacity annotations** on the MachineDeployment — CAPMOX does not publish
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`status.capacity` on `ProxmoxMachineTemplate`.
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