r12d

Problem

QR codes are everywhere, and most QR services make money by tracking whoever scans them. For a household labelling storage boxes, or a small business tagging equipment, that’s a bad trade. They need durable codes, an inventory behind them, and a way for an honest finder to report something lost. They don’t need an ad-tech profile of every scan.

Approach

One Django service with two faces, picked by the request’s host:

1. 01

   Sticker scan

   r12d.ch/<code>

   ↓→

2. 02

   Public host

   short codes, lost & found, marketing

   ↓→

3. 03

   Anonymous daily count

   no IP, no UA, no per-scan row

   ↓→

4. 04

   App host

   inventory, photos, CRM, loans

• No visitor tracking, by construction. No IP address, user agent or per-scan row is ever stored. Scans become anonymous daily counts. The public host sets no cookies for anonymous visitors, and the app server runs without an access log. A dedicated test suite guards everything the app can enforce.
• Workspaces as the tenancy boundary. Every query goes through one membership check, and child objects are always looked up scoped to that workspace, never by a bare ID. Non-members get a 404, not a 403, so the app doesn’t confirm that something exists.
• Permanent codes. A printed sticker can’t be recalled, so short codes are generated once and never reused. A code is deactivated, never deleted.

Hard parts

• Two hosts, one URL config. In production each host knows only its own routes, so a link that crosses hosts has to be built explicitly. Single-host tests miss that kind of bug, so a split-mode test exists for every cross-host path. That’s how a 500 error on every lost-and-found report was caught in review, before it shipped.
• Back office off the internet. The admin is reachable only over a private network. Ingress routes by Host header, so even an internal-looking hostname would be publicly reachable. The app rejects admin requests on every other host.

Outcome

• Live at r12d.ch, with the product on its own host.
• Privacy is a set of tested rules, not a promise on a marketing page.
• Ships through the same review-app → dev → prod pipeline as everything else on the homelab.

Stack