Delegating tasks to Fly Machines

Summary

Resource-intensive web tasks such as resizing high-resolution images can require substantially more memory or CPU than ordinary request handling, making an always-powerful web server inefficient. The article presents a framework- and language-agnostic delegation pattern using Fly Machines, the private network, and two process groups that run the same application with different Machine specifications. A Next.js route calls a wrapper that executes the task when FLY_PROCESS_GROUP is worker; otherwise, it sends a POST request to the identical endpoint through the worker’s internal hostname, returning the worker’s response. The example uses a lighter web group and a performance-4x worker group, with local development using separate ports and production routing over .internal addresses; the author calls the implementation naïve and suggests queues and worker timeouts to improve resilience and control worker availability.

Takeaways

1. 1

   The delegation wrapper checks FLY_PROCESS_GROUP to avoid forwarding when the request has already reached a worker.

2. 2

   Production requests reach the worker through a .internal hostname, while local development uses separate processes on ports 3000 and 3001.

3. 3

   The implementation is described as naïve; a queue could improve resilience, and timeouts could start or stop worker Machines as needed.