| Feature | Fly V2 | Fly V3 | | :--- | :--- | :--- | | Syntax | Callback-based ( callback(err, res) ) | Async/Await | | State | Volatile (lost on restart) | Persistent (disk-backed) | | Concurrency | Manual Promise.all | Built-in Fly.parallelMap | | Error Handling | .catch() blocks | Try/Catch with automatic retries |
async function handle(event) if (event.type === "TRANSACTION") return await processTx(event.data);
async function resilientCall(fn, retries = 5) for (let i = 0; i < retries; i++) try return await fn(); catch (err) if (i === retries - 1) throw err; const delay = Math.pow(2, i) * 1000; await Fly.sleep(delay);
// Bad: Sequential for (const item of list) await process(item);
// State persistence state consecutive_failures = 0
Fly V3 scripts support pre- and post-execution hooks. These are used for logging, rate limiting, or modifying payloads before they reach the main handler. 4. The Termination Routine Graceful shutdown is critical. This block ensures that all open file handles are closed and pending tasks are flushed before the script exits. Writing Your First Fly V3 Script: A Step-by-Step Guide Let’s assume you want to build a monitoring script that checks the health of three servers and restarts a service if latency exceeds a threshold. Step 1: Environment Setup Ensure the Fly V3 CLI is installed on your machine:
Fly V3 scripts operate in hostile environments (network flaps, API throttling). Implement exponential backoff natively:
Whether you are automating a crypto trading strategy, orchestrating a cloud infrastructure, or simply scraping data for a personal project, mastering the Fly V3 script will make you more efficient and your systems more robust.
