Add InstanceName parameter

[fd-jonathanlinn]

Adds the ability to customise the Name tag on the EC2 instances spawned by the ASG, defaults to "buildkite-agent" for backwards compatibility.

Might want to add a MinLength/MaxLength to this, happy to do so based on preferences.

[moskyb]

re: min and max length, i think we're fine to leave it as is and have that end of things enforced by EC2 - i'm sure that there are reasonable limits in place there. Given that the failure dynamics are largely the same - the cfn stack won't launch in either case - i don't think there's much point in enforcing it on our end 🤷

again though, keen to hear your thoughts on this :)

[fd-jonathanlinn]

Yeah agreed on length we could remove those, was mostly trying to play it safe. If we end up referencing StackName it's a moot point since it won't launch like you said

[ChrisLane]

Thanks @fd-jonathanlinn! Somehow I didn't see your mention of my issue but I'm glad to see that I can do this now.

@moskyb could https://buildkite.com/docs/agent/v3/elastic-ci-aws/parameters be updated please?
I notice this option isn't mentioned in the docs and since I build the stack using AWS CDK, I don't often get to see the actual template parameters in CloudFormation UI.