Cluster Bare Autoscaler

Introduction

Cluster Bare Autoscaler (CBA) automatically adjusts the size of a bare-metal Kubernetes cluster by powering nodes off or on based on real-time resource usage, while safely cordoning and draining nodes before shutdown.

This project is similar to the official Kubernetes Cluster Autoscaler, but with key differences:

• CBA does not terminate or bootstrap instances.
• Instead, it powers down and wakes up bare-metal nodes using mechanisms like Wake-on-LAN, or other pluggable power controllers.
• Nodes are cordoned and drained safely before shutdown.

CBA uses a chainable strategy model for deciding when to scale down a node. Strategies can be enabled individually or used together:

• Resource-aware strategy — checks CPU and memory requests and usage.
• Load average strategy — evaluates /proc/loadavg via a per-node metrics DaemonSet.

It is especially suited for self-managed data centers, homelabs, or cloud-like bare-metal environments.

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Features

• ✅ Pluggable scale-down and scale-up strategies
  • Multi-strategy chaining with short-circuit logic
  • Dry-run mode for testing (--dry-run)
• ✅ Resource-aware scale-down
  • Considers CPU and memory requests
  • Optionally uses live usage metrics
• ✅ Load average-aware scale-down and scale-up using /proc/loadavg
  • Supports aggregation modes: average, median, p75, p90
  • Separate thresholds for scale-up and scale-down decisions
  • CLI dry-run overrides:
    • --dry-run-cluster-load-down
    • --dry-run-cluster-load-up
• ✅ MinNodeCount-based scale-up to maintain minimum node count
• ✅ Cooldown tracking
  • Global cooldown period
  • Per-node boot/shutdown cooldowns
• ✅ Node eligibility filtering
  • Ignores nodes with label cba.dev/was-powered-off: true
  • Respects .Disabled flag in config.yaml
• ✅ Safe cordon and drain using Kubernetes eviction API
• ✅ Wake-on-LAN support for powering on bare-metal machines

Additional, optional services

• ✅ Metrics DaemonSet for per-node load average via /proc/loadavg
• ✅ Power-off DaemonSet for secure node shutdown via systemd socket activation
• ✅ Wake-on-LAN agent (wol-agent) for powering nodes via HTTP-triggered magic packets

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Quickstart

1. Label your managed nodes
   Apply a label to every node you want the autoscaler to manage:

   kubectl label node <node-name> cba.dev/is-managed=true

2. (Optional) Manually annotate MAC addresses
   This is needed if you use Wake-on-LAN (WOL) and cannot rely on auto-discovery:

   kubectl annotate node <node-name> cba.dev/mac-address-override=aa:bb:cc:dd:ee:ff

   If not manually annotated, MACs will be discovered from the node's local poweroff daemon Pod (via /mac) and stored in cba.dev/mac-address.

3. Install the autoscaler with Helm

   helm install cba cluster-bare-autoscaler/cluster-bare-autoscaler      -n <namespace>      -f values.yaml

4. Observe behavior in dry-run mode (optional)
   Run with --dry-run to observe decision logic without powering nodes.

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Node Definitions (via Annotations)

CBA automatically discovers nodes based on labels and manages them based on annotations.

• Required Label:
  Nodes must be labeled to be considered managed:
  cba.dev/is-managed: "true"

• Optional Exclusion Label:
  Add this label to skip specific nodes from scaling:
  cba.dev/disabled: "true"

• Annotations:

  Key	Purpose
  cba.dev/mac-address	Auto-discovered MAC address for WOL
  cba.dev/mac-address-override	Manually specified MAC (takes precedence)
  cba.dev/was-powered-off	Marked by autoscaler after shutdown

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Metrics

The autoscaler exposes Prometheus metrics on port :9090 at the /metrics endpoint.
Metrics include evaluation counts, shutdown attempts/successes, eviction failures, and per-node powered-off status.

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Installation

Using Helm

helm install cba cluster-bare-autoscaler/cluster-bare-autoscaler   -n <namespace>   -f values.yaml

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Configuration

All configuration is passed via a ConfigMap in YAML form.
The root config keys are defined in the values.yaml.

See the example config.yaml for details.

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Development

Build the binary

make build_binary

Run tests

make test

Build container image (multi-arch with ko)

make build_image
make publish_image

Run locally

go run main.go --config=./config.yaml --dry-run

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Roadmap & TODO

See TODO.md for the current feature backlog and development roadmap.

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License

MIT