API Gateway: Mapping Path Segments to SQS Message

Tue, Jun 29, 2021

Given an API Gateway endpoint such as POST - /{UserId}/{MessageId}/read and a requirement to push a message to SQS using just the values contained within the request path. We can create a Integration Request template that pulls these values and creates an SQS message with a JSON body containing these values.

Within the CloudFormation template where we have defined our API in Swagger/OpenAPI we can use the following request template to extract the UserId and MessageId and send a message to an SQS queue such as this:

{
  "UserId": "User1",
  "MessageId": "6c7c614a-eadc-4d5b-984b-49254627d275"
}

requestTemplates:
  application/json:
    Fn::Sub: |
      #set ($UserId = $input.params('UserId'))
      #set ($MessageId = $input.params('MessageId'))
      #set ($messageContent = "{ 'UserId': '$UserId', 'MessageId': '$MessageId' }")
      Action=SendMessage&QueueUrl=$util.urlEncode('${ReadMessageQueue}')&MessageBody=$messageContent

These templates are based on Apaches Velocity Template Language or VTL.

Just for completeness the full API Gateway resource definition in CloudFormation:

APIGateway:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Name: "Message System"
      EndpointConfiguration:
        Types:
          - REGIONAL
      Policy:
        - !Ref "AWS::NoValue"
      Body:
        swagger: '2.0'
        info:
          title: !Ref AWS::StackName
        paths:
          /{UserId}/{MessageId}/read:
            post:
              parameters:
                - in: path
                  name: UserId
                  required: true
                  type: string
                  description: User ID
                - in: path
                  name: MessageId
                  required: true
                  type: string
                  description: Message UUID
              consumes:
                - application/json
              produces:
                - application/json
              responses:
                '200':
                  description: 200 response
                  schema:
                    $ref: '#/definitions/Empty'
              x-amazon-apigateway-integration:
                credentials: !GetAtt APIGatewayRole.Arn
                uri: !Sub "arn:aws:apigateway:${AWS::Region}:sqs:path//"
                responses:
                  default:
                    statusCode: '200'
                requestParameters:
                  integration.request.header.Content-Type: '''application/x-www-form-urlencoded'''
                requestTemplates:
                  application/json:
                    Fn::Sub: |
                      #set ($UserId = $input.params('UserId'))
                      #set ($MessageId = $input.params('MessageId'))
                      #set ($messageContent = "{ 'UserId': '$UserId', 'MessageId': '$MessageId' }")
                      Action=SendMessage&QueueUrl=$util.urlEncode('${ReadMessageQueue}')&MessageBody=$messageContent                      
                passthroughBehavior: never
                httpMethod: POST
                type: aws
        definitions:
          Empty:
            type: object
            title: Empty Schema

API Gateway: Mapping Path Segments to SQS Message

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