Simple Stock Market

A simplified, highly available stock exchange REST API.

Stack

• API: Node.js + TypeScript (Express)
• State: Redis - shared across all instances
• Load balancer: Nginx - least_conn + automatic failover
• Orchestration: Docker Compose - 3 independent API replicas

Atomic buy/sell operations are implemented as a Redis Lua script to prevent race conditions under concurrent load.

Prerequisites

Docker must be installed and running. No other runtime is required.

Start

Linux / macOS

chmod +x start.sh
./start.sh 3000

Windows

start.cmd 3000

The API is available at http://localhost:3000.

To stop: docker-compose down

High Availability

Three API instances run behind Nginx. When /chaos kills one instance:

• Nginx detects the failure via proxy_next_upstream and retries on a healthy instance
• Docker restarts the killed container automatically (restart: unless-stopped)
• All state lives in Redis, so any instance can serve any request Killing one instance does not interrupt the service.

API

Bank

GET /stocks

Returns current bank inventory.

{ "stocks": [{ "name": "Apple", "quantity": 100 }] }

POST /stocks

Replaces the entire bank state.

{ "stocks": [{ "name": "Apple", "quantity": 100 }, { "name": "Google", "quantity": 50 }] }

Returns 200 Bank state updated.

Wallets

POST /wallets/{wallet_id}/stocks/{stock_name}

Buy or sell one unit of a stock. Creates the wallet if it does not exist.

Body:

{ "type": "buy" }

| Status | Reason | | 200 | Success | | 400 | No stock in bank (buy) / no stock in wallet (sell) | | 404 | Stock does not exist in the bank |

GET /wallets/{wallet_id}

Returns full wallet state.

{ "id": "alice", "stocks": [{ "name": "Apple", "quantity": 3 }] }

GET /wallets/{wallet_id}/stocks/{stock_name}

Returns a single quantity number.

3

Audit Log

GET /log

Returns all successful trade operations in order of occurrence. Bank resets are not logged.

{
  "log": [
    { "type": "buy",  "wallet_id": "alice", "stock_name": "Apple" },
    { "type": "sell", "wallet_id": "bob",   "stock_name": "Apple" }
  ]
}

Chaos

POST /chaos

Kills the instance that served the request. The remaining two instances continue handling traffic.