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Open sourcegobackendapisystem-design

Shillings

A Go backend that simulates a payment provider plus the surrounding identity and ledger primitives — split into independently scalable web and application layers that talk over a custom protocol.

Language
Go
Storage
MySQL + Redis
Edge
Nginx
Started
2022
Repository
shillings · mock payments backend

Shillings is a Go service that pretends to be a payment provider so you can test client integrations end-to-end without ever touching a real payments stack.

Architecture

The web layer and the application layer are deliberately separated so they can scale independently:

  • Web server — Handles incoming HTTP traffic, fronted by Nginx as a load balancer.
  • Application server — Owns business logic: authentication, payments, accounts.
  • MySQL — Stores user profiles, credentials, and the transaction ledger.
  • Redis — Caches user profiles for hot reads.
  • Protobuf — The two layers communicate over a custom protocol on top of Protobuf.

Everything ships as Docker images and comes up with a single make prod.

API surface

A minimal but realistic set of endpoints to integrate against:

  • POST /v1/signup and POST /v1/login — JWT-based auth.
  • GET /v1/account — current user profile and balance.
  • POST /v1/topup — credit the wallet.
  • POST /v1/pay — transfer between accounts.
  • GET /v1/transactions — paginated transaction history.

Why

Mostly to design and ship a cleanly-layered Go service end-to-end — schema, transport, deployment, the lot. Useful as a fixture for integration tests against a payments-like API without paying for sandbox access.