Before a single line of strategy logic runs, an algorithmic trader needs a reliable way to get market data in and orders out. This plumbing — the data pipeline and API integration — is unglamorous but is where the majority of live-trading bugs and outages actually originate.
REST vs. WebSocket
| REST | WebSocket | |
|---|---|---|
| Pattern | Request → response, one-off | Persistent connection, server pushes updates |
| Typical use | Placing orders, fetching historical bars, account state | Live price ticks, order book updates, order fill notifications |
| Latency | Higher — new connection/auth overhead per call | Low — connection stays open |
| Failure mode | Times out cleanly, easy to retry | Silent disconnects — needs heartbeat/reconnect logic |
Designing a Resilient Pipeline
- 1.Ingest — a WebSocket listener for live prices, with automatic reconnect and gap detection.
- 2.Normalize — convert vendor-specific formats (timestamps, symbol names) into one internal schema.
- 3.Store — append to a time-series database or partitioned files (e.g. Parquet) for later backtesting.
- 4.Validate — flag missing bars, duplicate ticks, and out-of-order timestamps before they reach strategy logic.
- 5.Serve — expose clean, validated data to backtesting and live strategy modules through one consistent interface.
Most broker and data-vendor APIs cap requests per second or per minute. A poorly written polling loop that hammers a REST endpoint can get your API key temporarily banned mid-session — exactly when you need live data most. Always implement exponential backoff and respect documented limits.
Order API Essentials
- ▸Idempotency keys — attach a unique client order ID so a retried request never double-submits an order.
- ▸Always reconcile — after every order action, query the broker's actual position/order state rather than trusting your local cache.
- ▸Sandbox first — every serious broker API offers a paper-trading endpoint; test the full pipeline there before touching real funds.
async function fetchWithBackoff(url, opts, attempt = 0) {
try {
const res = await fetch(url, opts);
if (res.status === 429) throw new Error('rate limited');
return res;
} catch (e) {
if (attempt >= 5) throw e;
await sleep(2 ** attempt * 500);
return fetchWithBackoff(url, opts, attempt + 1);
}
}The Bottom Line
Data pipelines and API integration rarely get credit when they work and get all the blame when they don't. Treat them with the same rigor as the trading logic itself — a great strategy fed stale or corrupted data will trade just as badly as a bad strategy.