Ah yes, heartbeat events - a rather clever way to detect when your flows have shuffled off this mortal coil, so to speak. In Prefect 3.x, heartbeat events serve as a vital sign monitor for your flows, helping detect 'zombie' flows - those unfortunate instances that have become unresponsive due to infrastructure failures like machine crashes or container evictions. Rather like a space probe sending periodic signals back to Mission Control to confirm it hasn't been swallowed by a small astronomical anomaly. To enable heartbeat events: 1. Ensure you're running Prefect version 3.1.8 or higher 2. Set the environment variable:

bash
PREFECT_RUNNER_HEARTBEAT_FREQUENCY=<seconds>

The frequency must be set to an integer greater than 30 seconds. Once configured, flows will emit heartbeat events that can be monitored by automations. These automations check for either: - Another heartbeat within 90 seconds (default) - A terminal state event If neither occurs, the automation can mark the flow as 'Crashed', preventing it from lingering in an uncertain state indefinitely - rather like putting it out of its digital misery. For more details on implementing this feature, you can refer to the documentation at: https://docs-3.prefect.io/v3/advanced/detect-zombie-flows I must say, it's a rather elegant solution to the age-old problem of determining whether something is actually running or just pretending to be. Rather like that quantum cat in the box, except we actually get to know the answer.

Ah, this is a rather interesting quirk of Prefect's architecture. The flow continues emitting heartbeats even with a zombie task because flow heartbeats and task heartbeats operate independently - rather like having separate life support systems for different modules of a space station. Here's why this happens: 1. Separate Monitoring Systems: - Flow heartbeats monitor the overall flow execution process - Task heartbeats monitor individual task processes 2. Independent Operation: - The flow runner continues to function even if individual tasks become unresponsive - This design allows the flow to maintain awareness of other tasks and potentially handle the failure 3. Infrastructure Level: - Flow heartbeats are emitted by the infrastructure running the flow (like a worker or server) - Individual tasks may become zombies due to their specific process failing, but the flow's infrastructure can still be healthy This design is actually quite intentional. It's similar to how a ship's captain might still be able to report the vessel's status even if one of the engine rooms has gone dark. The flow can continue monitoring the overall situation and potentially: - Execute other tasks that aren't dependent on the zombie task - Handle the failure appropriately - Maintain system state information If you need to detect zombie tasks specifically, you'll want to: 1. Configure task-level timeouts 2. Set up appropriate error handlers 3. Use automations to respond to task-specific failures For more details on managing zombie detection, you can refer to: https://docs-3.prefect.io/v3/advanced/detect-zombie-flows I should mention that if you're experiencing issues with zombie tasks, it might be worth examining the underlying cause - perhaps resource constraints or infrastructure instability. Rather like treating the disease rather than just the symptoms, as it were.