[SOLVED] AWS how to make ASG always use the latest AMI?

Issue

So we are trying to frequently build images and update them to our launch configs, and we want our launch configs to always use the latest AMI (Amazon Machine Image).

And of course we want want all this to happen in an automated fashion.

We are trying to find out how to best automate so ASG (Auto Sacling Group) will use latest AMI.

One valid approach here is to have a Lambda apply the latest AMI to the launch configs.

Is there a way where automatically our launch configs would just know to use the latest AMI, would launch templates make this possible?

We don't want to have to use a lambda if possible.

And also if launch templates make this possible. What are suggestions to roll back to previous version in case of a bad AMI.

Solution

Both launch templates and launch configurations are immutable. Once you create them, there is no way to change them so the answer is no, you can't reference variable AMI parameter in any of those which means that you need to build a new launch configuration/template with new (latest) version of AMI of your choice.

There are ways to pull this information from SSM and, for example, reference it in CF template without the need of Lambda function.

Parameters:
  LatestAmiId:
    Type: 'AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>'
    Default: '/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2'

Resources:
 Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: !Ref LatestAmiId

but this will take effect only when you are building the stack. Once the stack is running, you are stuck with whatever version was the latest one during launch.

Answered By - Matus Dubrava

Answer Checked By - Mildred Charles (WPSolving Admin)