macexporter

A small Prometheus exporter for macOS hosts. Exposes the metrics that the official Prometheus node_exporter and Apple's tooling don't make easy to surface together — CPU package power, CPU usage, real "memory used" (excluding reclaimable cache), and per-interface byte counters — over a single endpoint.

Built for headless Mac mini server racks; works on any macOS host.

Metrics

Name	Type	Source	Notes
dormlab_cpu_power_watts	gauge	powermetrics --samplers cpu_power	Requires running as root. Set --no-power to skip.
dormlab_cpu_usage_ratio	gauge	top -l 1 -n 0 (user + sys)	0..1
dormlab_memory_used_bytes	gauge	top PhysMem (wired + compressor)	Excludes reclaimable file-backed cache. Matches Activity Monitor's headroom view.
dormlab_memory_total_bytes	gauge	sysctl hw.memsize
dormlab_network_rx_bytes_total{iface}	counter	netstat -ibn Ibytes	Loopback skipped, deduplicated per iface.
dormlab_network_tx_bytes_total{iface}	counter	netstat -ibn Obytes	Same.
dormlab_nodeexporter_up{version}	gauge	always 1	Liveness for up{} queries.

Architecture

A background tokio task runs all four shell-out collectors concurrently (tokio::join!) every --refresh-secs seconds and updates a shared Prometheus Registry. The axum HTTP handler reads from the registry — no subprocesses run inside a request, so the /metrics scrape is fast and predictable even when powermetrics takes ~500 ms to sample.

Counters stay honest across rapid scrapes by tracking the previous absolute kernel value per interface and feeding inc_by(delta) to Prometheus, so rate() queries work normally and counter resets (iface reload, host reboot) are absorbed via saturating_sub.

Endpoints

• GET /metrics — Prometheus text exposition.
• GET /healthz — 200 ok if the process is alive.
• GET / — landing page with links to the above.

Build

cargo build --release --target aarch64-apple-darwin

Produces a single ~1.8 MB binary at target/aarch64-apple-darwin/release/dormlab-nodeexporter. No runtime dependencies — it shells out to powermetrics, top, sysctl, and netstat, all bundled with macOS.

cargo test --release --target aarch64-apple-darwin

CLI

Usage: dormlab-nodeexporter [OPTIONS]

Options:
      --bind <BIND>                   [env: DORMLAB_BIND=] [default: 0.0.0.0:9101]
      --refresh-secs <REFRESH_SECS>   [env: DORMLAB_REFRESH_SECS=] [default: 5]
      --no-power                      [env: DORMLAB_NO_POWER=]
  -h, --help                          Print help
  -V, --version                       Print version

Set RUST_LOG=dormlab_nodeexporter=debug for verbose logs.

Deploy as a LaunchDaemon

powermetrics requires root. Drop the included dev.dormlab.nodeexporter.plist into /Library/LaunchDaemons/ and bootstrap it:

sudo install -m 755 target/aarch64-apple-darwin/release/dormlab-nodeexporter \
  /usr/local/sbin/dormlab-nodeexporter
sudo install -m 644 dev.dormlab.nodeexporter.plist \
  /Library/LaunchDaemons/dev.dormlab.nodeexporter.plist
sudo launchctl bootstrap system /Library/LaunchDaemons/dev.dormlab.nodeexporter.plist

Logs go to /var/log/dormlab-nodeexporter.log.

Prometheus scrape config

scrape_configs:
  - job_name: macos-host
    static_configs:
      - targets:
          - mac-1.example.com:9101
          - mac-2.example.com:9101

The exporter listens on 0.0.0.0:9101 by default. Restrict at the firewall or with --bind 127.0.0.1:9101 plus a Tailscale / SSH tunnel if you care.

Why not the upstream node_exporter?

The Prometheus project's node_exporter works on macOS via a Darwin collector, but it's missing power metrics (no powermetrics integration) and its memory accounting reports the kernel's "active" pages rather than the user-meaningful "wired + compressor" view. This exporter intentionally covers a smaller surface — just the four things you usually want from a macOS host — and keeps the binary tiny.

License

MIT — see LICENSE.