feat: custom domains Api Gateway support

[praneetap]

Issue #, if available:
#1125, #1126, #1127, #783
Description of changes:
Adding basic custom domains handling to SAM. This only creates ApiGateway resources with a single basepath mapping to '/'
I found that I don't need to edit the swagger, APIGateway does this for me automatically when I create the BasePath Mappings.
Description of how you validated changes:
Tested deploying on CFN

Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #1144 into develop will increase coverage by 0.11%.
The diff coverage is 96.66%.

@@             Coverage Diff             @@
##           develop    #1144      +/-   ##
===========================================
+ Coverage    94.36%   94.47%   +0.11%     
===========================================
  Files           71       71              
  Lines         3621     3677      +56     
  Branches       713      726      +13     
===========================================
+ Hits          3417     3474      +57     
+ Misses         104      103       -1     
  Partials       100      100

Impacted Files	Coverage Δ
samtranslator/translator/verify_logical_id.py	100% <ø> (ø)	⬆️
samtranslator/plugins/globals/globals_plugin.py	100% <ø> (ø)	⬆️
samtranslator/plugins/globals/globals.py	99.02% <ø> (ø)	⬆️
samtranslator/model/apigateway.py	97.9% <100%> (+0.11%)	⬆️
samtranslator/model/sam_resources.py	95.56% <100%> (+0.07%)	⬆️
samtranslator/model/api/api_generator.py	96.51% <95.34%> (-0.21%)	⬇️
samtranslator/plugins/api/implicit_api_plugin.py	98.59% <0%> (+2.11%)	⬆️

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[jlhood]

Really excited to see movement on custom domain support! Lots of questions around edge case behavior. I don't think a single happycase test is sufficient here.

Also, are you planning to add an example as part of this PR?

[Jacco]

Just a note: I have a template with two AWS::Serverless::Api that share the same AWS::ApiGateway::DomainName each with a different AWS::ApiGateway::BasePathMapping.

I guess this solution does not support that?

Also found that using custom domains the AWS::ApiGateway::BasePathMapping needs a DepensOn on de Stage generated by AWS::Serverless::Api for succesful deploying

DependsOn:
  - BackofficeAPIStage

[praneetap]

@Jacco thanks for the feedback!

Just a note: I have a template with two AWS::Serverless::Api that share the same AWS::ApiGateway::DomainName each with a different AWS::ApiGateway::BasePathMapping.

I guess this solution does not support that?

No unfortunately this doesn't support referencing an existing DomainName. Sounds like this would be good to have.

Also found that using custom domains the AWS::ApiGateway::BasePathMapping needs a DepensOn on de Stage generated by AWS::Serverless::Api for succesful deploying

DependsOn:
  - BackofficeAPIStage

BasePathMapping references Api.Stage (this is a referable property exposed by SAM), which creates the necessary dependency chain. The BasePathMapping resource looks like this -

MyApiBasePathMapping:
    Type: AWS::ApiGateway::BasePathMapping
    Properties:
      DomainName: !Ref APIDomainName
      RestApiId: !Ref MyApi
      BasePath: one
      Stage: !Ref MyApi.Stage ## this creates the dependency

[keetonian]

Overall, looks good. This might be a silly question, but can you have multiple AWS::ApiGateway::DomainName resources that all have the same domain name + certificate but different logical Id's?

[praneetap]

Overall, looks good. This might be a silly question, but can you have multiple AWS::ApiGateway::DomainName resources that all have the same domain name + certificate but different logical Id's?

No, you can only create one ApiGateway DomainName per domain "www.example.com". CloudFormation deploy fails if you try to create another ApiGateway DomainName resource for an existing domain.

Addressed requested changes