Reference API Gateway Models in CloudFormation

Michael Wittig – 02 Sep 2016

API Gateway Models are defined using JSON Schema. You can reference a Model inside another Model using the $ref field. If you are familiar with the OpenAPI Specification fka Swagger, you may have seen something like this:

{
  "$ref": "#/definitions/User"
}

To make model references work with API Gateway, you need to provide an absolute reference that is predefined by AWS: https://apigateway.amazonaws.com/restapis/$ApiId/models/$ModelName

Let’s translate this to a CloudFormation template:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Lambda and API Gateway",
  "Resources": {
    "RestApi": {
      "Type": "AWS::ApiGateway::RestApi",
      [...]
    },
    "UserModel": {
      "Type": "AWS::ApiGateway::Model",
      "Properties": {
        "ContentType": "application/json",
        "Name": "User",
        "RestApiId": {"Ref": "RestApi"},
        "Schema": {
          "$schema": "http://json-schema.org/draft-04/schema#",
          "type": "object",
          "title": "User",
          "additionalProperties": false,
          "properties": {
            "uid": {
              "type": "string"
            },
            "email": {
              "type": "string"
            },
            "phone": {
              "type": "string"
            }
          },
          "required": ["uid", "email", "phone"]
        }
      }
    },
    "UsersModel": {
      "Type": "AWS::ApiGateway::Model",
      "Properties": {
        "ContentType": "application/json",
        "Name": "Users",
        "RestApiId": {"Ref": "RestApi"},
        "Schema": {
          "$schema": "http://json-schema.org/draft-04/schema#",
          "type": "array",
          "title": "Users",
          "items": {
            "$ref": {"Fn::Join": ["", ["https://apigateway.amazonaws.com/restapis/", {"Ref": "RestApi"}, "/models/", {"Ref": "UserModel"}]]}
          }
        }
      }
    },
    "RestApi": {
      "Type": "AWS::ApiGateway::RestApi",
      "Properties": {
        "Name": "API Gateway ToDo"
      }
    }
  }
}

That’s it. Now you can build sophisticated API Gateway models that reference each other in CloudFormation.

Michael Wittig

I’ve been building on AWS since 2012 together with my brother Andreas. We are sharing our insights into all things AWS on cloudonaut and have written the book AWS in Action. Besides that, we’re currently working on bucketAV, HyperEnv for GitHub Actions, and marbot.

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Reference API Gateway Models in CloudFormation

Michael Wittig

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