Some EC2 Time Out During Maintenance Window Execution

Hello,

Here are a few ideas to help you debug the issue:

• What do the logs say?
• Is the SSM Agent running and up-to-date on the failed instances? Checks the logs of the agent as well with the following command: journalctl -u amazon-ssm-agent
• Are all the instances in the same VPC, subnets, and using the same security groups? It's not mandatory, but it can help you understand why some instances timed out while others didn't. For example, the successful EC2 instances might have a port open that is not open on the failed ones.

Look for differences between the successful and failed instances.

Hope this helps 😊

The issue you're experiencing with some EC2 instances timing out during the maintenance window execution for patching tasks is not uncommon. There are several potential reasons why this might occur:

1. Connectivity Issues: Some instances may have lost connection to Systems Manager during the patching operation. This can happen due to network interruptions or if the Systems Manager Agent (SSM Agent) on the instance encounters problems.

2. Instance Availability: Some of the EC2 instances might have been offline or stopped during the maintenance window operation.

3. Resource Constraints: If the instances that timed out have less resources (CPU, memory) compared to the successful ones, they might take longer to complete the patching process.

4. Patch Complexity: The instances that timed out might require more complex or numerous patches, causing the process to exceed the timeout limit.

5. Instance Workload: If the failing instances were under heavy load during the patching process, it could slow down the patching operation.

To address this issue, you can try the following:

1. Increase the timeout: The current timeout of 10800 seconds (3 hours) might not be sufficient for all instances. Consider increasing this value.

2. Check instance health: Ensure all target instances are online and functioning correctly before the maintenance window starts.

3. Review SSM Agent: Make sure the SSM Agent is up-to-date and running properly on all instances.

4. Examine logs: Look at the Systems Manager logs on the failed instances to identify any specific issues that might have caused the timeout.

5. Stagger patching: If resource contention is an issue, consider creating multiple maintenance windows to patch smaller groups of instances at a time.

6. Manual patching: For the instances that failed, you can manually run the maintenance window tasks on these resources.

If the problem persists, you might want to investigate the specific characteristics of the failing instances (e.g., their size, workload, or network configuration) to identify any patterns that could explain the timeouts.
Sources
Troubleshooting maintenance windows - AWS Systems Manager
Patching schedules using maintenance windows - AWS Systems Manager