Updating the AMI used for ECS EC2 Machines

Updating the AMI for your EC2-backed ECS clusters and transitioning from Launch Configurations to Launch Templates is a relatively straightforward process, but it does require careful planning and execution.

To update your ECS clusters to use the latest Amazon ECS-optimized AMI and switch to Launch Templates, you can follow these general steps:

1. Create a new Launch Template: This will replace your existing Launch Configuration. In the Launch Template, you can specify the latest Amazon ECS-optimized AMI, which includes the most up-to-date versions of Amazon Linux, Docker, ecs-init, and the Amazon ECS container agent.

2. Update your Auto Scaling Group: Modify your Auto Scaling Group to use the new Launch Template instead of the old Launch Configuration.

3. Perform an instance refresh: This process will gradually replace your existing EC2 instances with new ones based on the updated Launch Template. The instance refresh helps you to relaunch EC2 instances in the Auto Scaling Group using the new Launch Template that references the latest version of the Amazon ECS optimized AMI.

Regarding the security group, when you create a new Launch Template, you have the option to specify the security group. You can indeed set it to use the existing security group that your instances are currently using. This way, you maintain the same network security settings for your new instances.

It's important to note that updating your instances will cause running tasks to be stopped and replaced. To minimize disruption, you should consider using Amazon ECS's managed instance draining feature. This feature automatically drains tasks from EC2 instances that are set to be terminated, preventing new task launches on these instances and proactively replacing existing tasks onto new hosts.

When planning this update, also consider the following:

1. Test the process in a non-production environment first.
2. Ensure your new AMI is compatible with your existing workloads.
3. Plan for potential downtime or service interruptions during the update process.
4. Monitor the update process closely to ensure tasks are properly drained and restarted on new instances.

By following these steps and considerations, you can successfully update your ECS clusters to use the latest AMI and transition to Launch Templates.
Sources
Amazon ECS enables easier EC2 capacity management, with managed instance draining | Containers
Community | Easier EC2 instance maintenance with managed draining for Amazon ECS capacity providers
Amazon ECS-optimized Linux AMIs - Amazon Elastic Container Service