SAM - Creating a new API Gateway with an existing Custom Domain

Question

We are exploring using SAM for deployment and we want to use a single custom domain (e.g. `api.example.com`) and create a base path per microservice (e.g. `api.example.com/svcA` and `api.example.com/svcB`). Each microservice is its own project/repo and we want to keep it that way.   
  
In working with SAM we found that it will always try to create the custom domain instead of using an existing one. This causes microservices to be undeployable because they try to create a custom domain that already exists.  
  
Is it possible to do what I want? Is there an example of how to accomplish this?

Answer

This ended up being very easy to accomplish. I had been focused on the custom domain part so much I overlooked that I could simply create a BasePathMapping. The following worked fine for me:

```
  BasePath:
    Type: AWS::ApiGateway::BasePathMapping
    Properties:
      BasePath: my-service
      DomainName: !Ref DomainName # I pass this in as a parameter per environment.
      RestApiId: !Ref MainApi  # This is my AWS::Serverless::Api resource
      Stage: default
```

Edited by: StealthSid2 on Jul 16, 2020 12:12 PM

SAM - Creating a new API Gateway with an existing Custom Domain

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