50. Capstone: designing a Node backend for a dApp

A production-grade Node backend for a dApp typically layers several of this track's topics: an Express-style API with validated routes (topics 25-27), configuration driven by environment variables per chain (topics 7, 24, 44), an indexer polling or subscribing to chain data into a database (topics 29-30, 43), caching for hot reads (topic 33), structured logging and health checks (topics 28, 46), and graceful shutdown plus retry/backoff around every external call (topics 32, 35).

js
async function main() {
  const config = loadConfig();       // fail fast if misconfigured
  const db = await connectDb(config.databaseUrl);
  const app = buildApp({ db, config });
  const server = app.listen(config.port);

  startIndexer({ db, rpcUrl: config.rpcUrl }).catch((err) => log("error", "indexer crashed", { err: err.message }));

  process.on("SIGTERM", async () => {
    server.close();
    await db.close();
    process.exit(0);
  });
}

main().catch((err) => { console.error("fatal startup error:", err); process.exit(1); });

None of these pieces is exotic in isolation — the skill this capstone tests is composing them into a service that stays correct and observable under real network conditions: slow RPC nodes, restarts, and traffic spikes.

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