asyncio in Production: Never Block the Event Loop — TaskGroups, Cancellation and Bounded Concurrency

A practical asyncio guide for Python services in production: why blocking the event loop degrades the whole process without raising a single exception, how to catch it by measuring loop lag and with Python 3.14 introspection, structured concurrency with TaskGroup and handling ExceptionGroup via except*, the task the garbage collector makes vanish, timeouts with a deadline budget propagated across services, correct cancellation with cleanup and shield, bounded concurrency with semaphores and backpressured queues, synchronization primitives, and what changes with eager tasks, python -m asyncio pstree and free-threading. With production-ready code and a deployment checklist.