<@ULVA73B9P> I'm running Prefect workers on AWS EC...
# ask-marvin
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@Marvin I'm running Prefect workers on AWS ECS with autoscaling enabled. When ECS autoscaling triggers a scale-in event, the tasks are terminated immediately without allowing the Prefect workers to finish their current flows. This causes zombie flows and data loss. Question: Does prefect worker have built-in graceful shutdown handling for SIGTERM signals? Can I use it to handle ECS task termination gracefully and avoid zombie flows?
m
thought for 47.9 seconds
Based on the research and GitHub issues, I can provide a comprehensive answer about Prefect worker shutdown handling in ECS: Yes, Prefect workers do have built-in graceful shutdown handling for SIGTERM signals. However, there are some important considerations for ECS environments: 1. Built-in SIGTERM Handling: - Prefect workers are designed to handle SIGTERM signals by initiating a graceful shutdown - When a SIGTERM is received, the worker: 1. Logs a shutdown message 2. Calls its internal stop method 3. Performs a clean exit procedure 2. ECS Configuration Requirements: To properly handle task termination in ECS, you need to configure two critical settings: - Set an appropriate
stopTimeout
in your ECS task definition (recommended 120-180 seconds) - Configure your ECS service's auto-scaling cool-down periods to allow for graceful termination 3. Best Practices for ECS:
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json
   {
     "containerDefinitions": [{
       "stopTimeout": 120,
       // other configuration...
     }]
   }
4. Additional Recommendations: - Monitor your worker logs for shutdown signals - Consider implementing health checks that respect the shutdown state - Use ECS capacity providers with appropriate termination protection settings However, there's an important caveat: While Prefect workers handle SIGTERM gracefully, the effectiveness depends on ECS giving enough time for the shutdown process. If ECS forcefully terminates the container before the graceful shutdown completes, you may still experience zombie flows. To fully protect against zombie flows, you should: 1. Ensure your ECS task definition includes adequate stop timeout values 2. Configure your auto-scaling policies with appropriate cool-down periods 3. Monitor for premature terminations and adjust timeouts as needed 4. Consider using ECS capacity providers that support managed termination protection If you're still experiencing issues after implementing these recommendations, you might want to: 1. Increase your ECS task definition's
stopTimeout
2. Review your auto-scaling policies to ensure they're not too aggressive 3. Implement additional monitoring to track when/how tasks are being terminated Would you like me to provide more specific details about any of these aspects or help with configuring your ECS task definitions?