Pizzaville

An ordering system for a food fair: tills, kitchen screens, pickup boards, printers and a phone app for customers. When the internet went down, the selling didn't stop.

Django
Channels + Redis
Postgres
Vue 3
Docker
Cloudflare tunnel
Fly + Neon

Everything is on. Switch a part off.

Fig. 1The fair keeps selling with the cable unplugged.

Fig. 2One order, from phone to plate.

✓ PaidOrder number given.
? UnknownNo number given. Retrying is safe.
✕ Not paidNothing was created.

Fig. 3"Unknown" is a real answer.

Charged only once the order exists
Authorise the card, create the order at the fair, then capture. If the fair says no, the hold is voided: no refund to chase.
"Unknown" is a real answer
If the connection drops mid-sale, the app says it doesn't know. Retrying can't create a second order.
Screens for where they hang
A till at arm's length, a kitchen monitor at three metres, a pickup board at six.

orders in four nights: 9k+
from the customer web app: 4.8k+
nights: 4
downtime: 0