Need to configure serverless resource output to get api gateway api id - aws-api-gateway

Question

I have a serverless project that is creating an API Gateway API amongst other things. One of the functions in the project needs to generate a URL for an API endpoint.
My plan is to get the API ID using a resource output in serverless.yml then create the URL and pass it through to the lambda function as an env parameter.
My problem/question is how to get the API ID as a cloud formation output in serverless.yml?
I've tried:
resources:
Outputs:
RESTApiId:
Description: The id of the API created in the API gateway
Value:
Ref: name-of-api
but this give the error:
The CloudFormation template is invalid: Unresolved resource dependencies [name-of-api] in the Outputs block of the template

Answer 1

You can write something like this in the serverless.yml file:
provider:
region: ${opt:region, 'eu-west-1'}
stage: ${opt:stage, 'dev'}
environment:
REST_API_URL:
Fn::Join:
- ""
- - "https://"
- Ref: "ApiGatewayRestApi"
- ".execute-api."
- ${self:provider.region}
- Ref: "AWS::URLSuffix"
- "/"
- ${self:provider.stage}"
Now you can call serverless with optional commandline options --stage and/or --region to override the defaults defined above, e.g:
serverless deploy --stage production --region us-east-1
In your code you can then use the environment variable REST_API_URL
node.js:
const restApiUrl = process.env.REST_API_URL;
python:
import os
rest_api_url = os.environ['REST_API_URL']
Java:
String restApiUrl = System.getenv("REST_API_URL");

Answer 2

The serverless framework has a documentation page on how they generate names for resources.
See. AWS CloudFormation Resource Reference
So the generated RestAPI resource is called ApiGatewayRestApi.

Answer 3

Unfortunately, the documentation doesn't mention it:
resources:
Outputs:
apiGatewayHttpApiId:
Value:
Ref: HttpApi
Export:
Name: YourAppHttpApiId