Gebos/README.md

Gebos

IoT telemetry stack on bare-metal NixOS.

This repo is a monorepo containing all code, NixOS modules, host configurations, and CI/CD pipelines for the project. Everything is one flake.nix.

Architecture

Three hosts (see issue #21 for the full design discussion):

Host	Role	Public hostname	Private IP
mqtt-ingest	EMQX broker + Go MQTT→Postgres ingester	ingest.gebos.online	10.0.0.4
db-host	Postgres 17 + TimescaleDB (telemetry+auth)	db.gebos.online (SSH only)	10.0.0.2
app-host	Caddy + Kong + Supabase (compose) + SPA	app.gebos.online, api.gebos.online	10.0.0.3

Public REST surface is PostgREST + SQL /rpc/ functions, fronted by Kong, TLS-terminated by Caddy. Supabase Studio is bound to 127.0.0.1 on app-host — reach it with ssh -L 3000:127.0.0.1:3000 app-host.

Networking

There is no private DNS. Each host has a public hostname (used for deploy-rs SSH access from the Gitea runner, which is not on the private network, plus TLS ingress where applicable), and a static 10.0.0.0/8 IP used for all host-to-host traffic:

• db.gebos.online is for SSH/deploy only — Postgres is never exposed publicly.
• app-host and mqtt-ingest reach Postgres at 10.0.0.2:5432 over the private network.
• db-host only accepts Postgres (port 5432) from 10.0.0.0/8 (firewall rule in nix/hosts/db-host.nix).

MQTT ingest path

How a sender device's telemetry reaches Postgres, and the reasoning behind each choice. The device firmware is the fixed end of this contract, so the rest of the stack is built to match it rather than the other way around.

device ──MQTTS:8883──▶ EMQX (native TLS) ──MQTT:1883 loopback──▶ ingester ──▶ Postgres
         acrios/<IMSI>/<metric>            authn + ACL              IMSI→tenant

Broker: EMQX in the official container, deny-by-default auth

EMQX runs as the official emqx/emqx image via oci-containers with host networking (nix/modules/gebos-emqx.nix). Authentication uses the built-in database, seeded from a users.csv rendered by sops-nix (services.gebos.secrets.emqx) and bootstrapped on first start; the bootstrap only inserts users that don't exist yet, so a password rotation means deleting the user (dashboard or emqx ctl) and restarting to re-import. Authorization is a static acl.conf with no_match = deny. Passwords are plaintext in the CSV because the file is already an encrypted secret at rest and 0400 at runtime.

There are three broker users: ingester (subscribes the device tree), admin (break-glass, is_superuser — bypasses the ACL), and bender (the shared device account, below).

Topic scheme: the device's acrios/<IMSI>/… is the source of truth

Senders publish to acrios/<IMSI>/<metric> — mqtt_topic_base plus the SIM's IMSI plus the metric name. We adopted that namespace verbatim rather than reshaping it into the t/<tenant>/d/<device>/… form the schema originally imagined, because the firmware can't emit our tenant_id/device_id UUIDs — it only knows its IMSI. So the IMSI is the natural device key, and the ingester (subscribed to acrios/#) will resolve IMSI → (tenant_id, device_id) via a device registry before inserting into public.telemetry. That registry table and the ingester's topic parsing are still TODO — the ingester is currently a stub.

Device auth: shared user now (Option A), per-device later (Option B)

The sender logs in with a single shared account (bender), authorized to publish/subscribe under acrios/#. Tenant isolation is therefore enforced downstream by the ingester's IMSI registry, not at the broker — any device could publish under any IMSI. That's an accepted trade-off for a small trusted fleet, and it gets data flowing without per-device provisioning.

The production answer (Option B, a TODO in nix/modules/gebos-emqx.nix) is one broker user per device with username == IMSI, scoped to acrios/${{username}}/# so the broker itself prevents a device from spoofing another's IMSI. It's not wired up because it needs a firmware change (mqtt_user = <IMSI>) and a per-device password provisioning flow. Note the firmware's client-id (acrcv-<IMSI>) carries a prefix the topic doesn't, so per-device scoping must key on username, not ${{clientid}}.

TLS: EMQX terminates natively, certs via ACME HTTP-01

EMQX terminates TLS itself on :8883; the plain MQTT listener stays on loopback for the co-located ingester. Certificates come from security.acme using the HTTP-01 challenge: lego's built-in standalone server answers on :80 (nothing else listens there — no Caddy on this host), so no DNS API secrets are needed. mqtt-ingest opens 80 + 8883 only. The cert's postRun hook installs fullchain.pem/privkey.pem at fixed paths in the broker state dir, and EMQX re-reads the PEMs from disk (~every 120 s), so renewals hot-reload without a restart or dropped connections. The key is RSA (keyType = "rsa2048") because embedded sender TLS stacks often can't do ECDSA. Caddy remains only on app-host (stock build, HTTP sites).

Repo layout

flake.nix
frontend/                # Vite + React SPA
ingester/                # Go MQTT → Postgres
nix/
  modules/               # NixOS modules (one per service)
  hosts/                 # nixosConfigurations: mqtt-ingest, db-host, app-host
  supabase/              # vendored Supabase docker-compose, db init SQL
  dev/                   # process-compose for local development
  deploy.nix             # deploy-rs node map
.gitea/workflows/        # CI + CD

Local development

nix run .#dev

Brings the full stack up on one machine via process-compose-flake (Postgres, Supabase compose, Kong, Caddy, ingester, Vite dev server). NixOS required.

Deployment

There are two distinct phases. Initial provisioning turns a blank box into a NixOS host (nixos-anywhere, run once per machine). Updates push new closures to a host that already runs NixOS (deploy-rs, run on every change).

SSH key setup (do this first)

Both phases authenticate over SSH with ~/.ssh/larsnolden, which is passphrase-protected. Load it into an ssh-agent once so the deploy tools can reuse it without prompting:

eval (ssh-agent -c)        # bash/zsh: eval "$(ssh-agent -s)"
ssh-add ~/.ssh/larsnolden  # enter the passphrase once
ssh-add -l                 # confirm the key is loaded

This is required for deploy-rs, not just a convenience: with magicRollback = true (see nix/deploy.nix) activation opens two concurrent SSH connections — the activation command and a rollback waiter. Without an agent, both race to read the passphrase from the terminal, one loses, and the deploy fails with Permission denied (publickey,keyboard-interactive) even though manual SSH and the copy step work. The agent serves the key to every connection, so no prompt is needed.

Initial provisioning (nixos-anywhere)

deploy-rs only updates a machine that already runs NixOS — it copies a prebuilt closure and activates it. A fresh box (e.g. a stock Debian image with only a root user) has no Nix store and no NixOS generation to switch to, so deploy-rs fails with nix-store: command not found. Use nixos-anywhere to install NixOS over SSH first; after that, deploy-rs takes over for all subsequent deploys.

nixos-anywhere SSHes in as root, kexecs into an in-memory NixOS installer, partitions and formats the disk per the host's disko config, installs nixosConfigurations.<host>, and reboots into NixOS. This wipes the target disk.

Prerequisites, per host, before running it:

1. A real disk layout. Hosts currently import the fictional nix/hosts/placeholder-hardware.nix (it only exists so nix flake check evaluates). Replace that import with a disko config describing the actual disk device (/dev/sda vs /dev/vda/nvme) and firmware (UEFI vs legacy BIOS). disko replaces the hand-generated hardware-configuration.nix.
2. Root SSH access to the box. The deploy user and its authorized keys are created by nix/hosts/common.nix during the install, so deploy-rs access works automatically once NixOS is up.
3. Host secrets key present so sops-nix can decrypt at first boot — see nix/secrets/README.md. Otherwise services that read /run/secrets/* (e.g. the ingester) fail to start after reboot.

Then, from the repo root:

# installs NixOS onto the target, wiping its disk
nix run github:nix-community/nixos-anywhere -- \
  --flake .#mqtt-ingest root@ingest.gebos.online

Repeat with .#db-host root@db.gebos.online and .#app-host root@app.gebos.online. Provision db-host first if you intend to deploy updates immediately afterward (see the ordering note below). Once a host has rebooted into NixOS, never run nixos-anywhere against it again — use deploy-rs.

Updates (deploy-rs)

deploy-rs from a Gitea Actions runner on push to main. Closures are built once, copied to each host, activated with auto-rollback. Order: db-host → app-host → mqtt-ingest.

Running it by hand needs the key loaded into an ssh-agent first — see SSH key setup above.

nix run github:serokell/deploy-rs -- .#db-host       # one host
nix run github:serokell/deploy-rs -- .                # all hosts

Secrets

sops-nix + age. Single encrypted file at nix/secrets/secrets.yaml; each host decrypts only the keys it needs at activation, rendered into a tmpfs env file consumed by systemd EnvironmentFile=. Plaintext never enters the Nix store. See nix/secrets/README.md for bootstrap and rotation.

Local dev needs no secrets bootstrap — nix run .#dev, go run ./ingester, and npm --prefix frontend run dev all default to the local dev stack values defined in nix/dev/process-compose.nix.