Add AWS ECS to cloud platforms

[vpavic]

This commit adds support for detecting AWS ECS to CloudPlatform. The detection is based on presence of AWS_EXECUTION_ENV environment variable with value starting with AWS_ECS.

Related resources:

• https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-environment-variables.html
• https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars.html

[wilkinsona]

Thanks for the suggestion. What about EC2 (and any other deployment option other than ECS and Lambda that there may be now or in the future)? AWS feels rather broad to me.

[vpavic]

If EC2 is the underlying ECS runtime, that gets picked up using AWS_EXECUTION_ENV (see the first link). If you're referring to the bare EC2, I think you have to make a call to instance metadata service. But that's a plain VM you need to manage manually either way, so I'm not sure it qualifies as a true cloud platform.

AWS as CloudPlatform option might be broad, but as a developer you probably just want to reliably figure out you're running on AWS so that you prepare some group of configuration properties using spring.config.activate.on-cloud-platform. I'm not sure what would be a use case for a more precise detection.

[wilkinsona]

We need to consider more than spring.config.activate.on-cloud-platform. For example, there's @ConditionalOnCloudPlatform as well. If the platform's named AWS, I think it sets the expectation that @ConditionOnCloudPlatform(CloudPlatform.AWS) would match whenever the app is deployed to AWS. That isn't the case and, therefore, I think the proposed name is misleading.

[vpavic]

I see. In that case, I can update this PR to focus on ECS - that can be detected quite accurately (using AWS_EXECUTION_ENV value) and is also the most popular option on AWS for running Spring Boot applications (see #47483).

I'm not sure detecting AWS Lambda using similar mechanism is worth it, as lambdas are quite coupled to the runtime either way.