Hey everyone! I'm working on a project that uses an autoscaling group of EC2 instances running a Python process. This process reads messages from an SQS FIFO queue, where it processes messages one at a time based on their group IDs. My autoscaling triggers are based on the queue size metric in CloudWatch.
The issue I'm facing is ensuring that the Python process completes processing a message before the instance gets shut down. I'm considering setting up a signal handler in my Python code, specifically for SIGINT, to indicate no more messages should be processed and allow the current message to finish before exiting the loop when an autoscaling down event occurs.
Here are my specific questions:
1. Are there any lifecycle events in EC2 or other mechanisms that can signal my Python process to finish before the instance is terminated, specifically during autoscaling down events?
2. If I transition to Docker and use Fargate, how would I implement a similar shutdown process?
3 Answers
Using lifecycle hooks is definitely the way to go! You can trigger a Lambda function when the instance is about to be terminated. This function can send a signal to your Python script, allowing it to complete its current task and exit safely.
It's a good practice to handle SIGTERM in your application to ensure it shuts down gracefully. For Fargate, when you terminate a task, it will send a SIGTERM signal which you can handle the same way.
You might want to use lifecycle hooks for the autoscaling group. This way, the ASG will wait for your hook to finish before it terminates the instance. Check out AWS's documentation on lifecycle hooks for more details on how to implement this!
Thanks! So, in Fargate, I can rely on SIGTERM to handle shutdowns gracefully while processing the last message?