This one is genuinely for me. It runs the house I live in, and it has been up for a fortnight without anyone touching it.
The organ model
Eighteen single-file Python daemons, each hardened as a systemd unit and named after an organ. It sounds whimsical and it is, but it produces a useful property: every process does one thing, restarts independently, and can be reasoned about on its own. Two more run as timers rather than services, because a nightly backup and a disk-health check are events, not processes.
Between all eighteen there is exactly one third-party Python dependency —
tinytuya, which two of them import to talk to Tuya devices on the local
network. Everything else is the standard library. That is not asceticism for its
own sake. A dependency here is something that will eventually need updating on a
machine I would rather not think about, and the standard library is the only
thing I can be confident will still import in five years.
boiler-bot is the heart. It drives a Shelly 1 Mini Gen3 into an Alpha InTec
28XE combi with degree-day-gated comfort windows, optimum start, a frost stat,
anti-short-cycle protection, a maximum-on cap and a running cost figure. Those
last few are not features, they are safety paths: software that controls a gas
appliance needs to fail closed.
apollo-vitals is the hippocampus, writing five-minute samples to a CSV and
events to a JSONL file, so state survives a reboot. Around them sit air quality,
doorbell, TV, circadian lighting, presence, network watch, printer and a
watchdog.
What was hard
Memory. 955 MB is the entire budget and every organ shares it, so the interesting engineering is in deciding what happens when something wants more than exists.
Every unit runs under ProtectSystem=strict and ProtectHome=read-only with an
explicit list of the paths it is allowed to write, so a bug in one organ cannot
reach another's state. More usefully, each one carries a deliberate OOM score.
The organs that keep the house running sit at negative scores, which puts them
among the last things the kernel will reap. Anything merely useful sits positive
and volunteers to die first.
That ranking earns its keep. This website is now built on the same Pi, and a production build peaks around 800 MB of the 955 — close enough to the edge that without the ranking, publishing a new case study could plausibly turn the heating off. Instead the builder is the first thing the kernel kills and the house does not notice.
The unusual part
There is a mind/ directory holding an identity stack and memory index that a
resident AI boots from every session — so the context travels with the repository
rather than living in someone's chat history.
The newest organ is the one that publishes this site. The editor for louisreed.co.uk runs on the Pi alongside the boiler and the doorbell, which means the house now maintains the page describing it.