How to get stack output from AWS SAM?

I would like to perform automatic integration tests on my serverless projects. To do that, I need to get the api endpoints somehow. There is already the plugin serverless-stack-output for Serverless framework that serves the purpose. But I'm wondering how can I achieve similar thing by AWS SAM after I deploy my application?

Meanwhile, If I can somehow get my api's base url as well as individual endpoints, then I'm able to connect them and and perform tests against them.

Solution

As AWS SAM builds upon AWS CloudFormation you can use CloudFormation's Outputs-feature.

How to define such outputs is pretty straight forward. You can e.g. refer to the "hello world" template in the SAM-template-repository. The relevant section is the definition of the outputs:

Outputs:
  HelloWorldApi:
    Description: "API Gateway endpoint URL for Prod stage for Hello World function"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hello/"

You then still need a way to get the outputs after you deployed the CloudFormation stack. For that you can e.g. use the AWS CLI:

aws cloudformation describe-stacks --stack-name mystack \
    --query 'Stacks[0].Outputs[?OutputKey==`HelloWorldApi`].OutputValue' \
    --output text