Simple API gateway with Mock response defined in SAM? - amazon-web-services

Question

I have a simple API gateway definition in AWS.
It has a single Method for "/" with a "GET" HTTP type.
I've updated the "Integration Request" to be a "Mock" (return a response purely with API Gateway mappings ...).
There's nothing fancy, all requests will be passed through.
For the response, I've updated the default Integration Response ( response status 200, no regex, model etc. Default mapping).
It has an "application/json" Mapping template, and in here i have just added the static text "hello world" (creative, i know).
Now, the question is, can i define this in a SAM template ?
I can readily find plenty of exmaples to create a lambda function behind this and have it do the response and all sorts of other things.
I can run the SAM cli locally to do "sam deploy" giving the sam template, and have a whole new AWS Stack created in my account, with the API Gateway created, the lambda python or javascript or etc uploaded to s3 and created and linked in to the API (through implicit sam definition, no external oas/swagger looked at yet) and roles etc created.
And it all works beautifully.
But if I want to do the same thing, but simpler - with just API gateway only and a mock integration response (no lambda) - what would the SAM template look like for that ?
As of yet, i am at a loss.
I can see from the serverless model that a lot of the integrations are supported in sam (x-amazon-apigateway-integration response).
I can see what the oas version looks like by using "api-gateway getexport" via the aws cli.
But I can not see a SAM template with implicit API creation that has no lambda linked in, just a simple Mock and static integration response.
Any help appreciated !!

Answer 1

SAM is a extension of Cloudformation, so yeah, it is possible, if you create a sam application and add the bellow template.yaml file, and run sam deploy --guided you will create what you need. In this case you will be running a simple cloudformation template that can be deployed with the following command:
aws cloudformation deploy --stack-name mock-api --template-file template.yaml
The main idea of SAM is facilitate the deploy of Serverless aplications, creating a possibility of invoke Lambda functions locally, improve debugging and so on, while provisioning your resources.
As we can see in the AWS documentation:
A serverless application is a combination of Lambda functions, event sources, and other resources that work together to perform tasks. Note that a serverless application is more than just a Lambda function—it can include additional resources such as APIs, databases, and event source mappings
So, if you are not using Lambda and you want provision your resources, you can simply use Cloudformation or another IaC tool as Terraform.
template.yml example (of what you need):
AWSTemplateFormatVersion: '2010-09-09'
Description: AWS API Gateway with a Mock Integration
Resources:
ApiGatewayRestApi:
Type: AWS::ApiGateway::RestApi
Properties:
ApiKeySourceType: HEADER
Description: An API Gateway with a Mock Integration
EndpointConfiguration:
Types:
- EDGE
Name: mock-api
ApiGatewayResource:
Type: AWS::ApiGateway::Resource
Properties:
ParentId: !GetAtt ApiGatewayRestApi.RootResourceId
PathPart: 'mock'
RestApiId: !Ref ApiGatewayRestApi
ApiGatewayMethod:
Type: AWS::ApiGateway::Method
Properties:
ApiKeyRequired: false
AuthorizationType: NONE
HttpMethod: POST
Integration:
ConnectionType: INTERNET
IntegrationResponses:
- ResponseTemplates:
application/json: "{\"message\": \"OK mock response\"}"
SelectionPattern: '2\d{2}'
StatusCode: 200
- ResponseTemplates:
application/json: "{\"message\": \"Internal Server Error mock response\"}"
SelectionPattern: '5\d{2}'
StatusCode: 500
PassthroughBehavior: WHEN_NO_TEMPLATES
RequestTemplates:
application/json: "{\"statusCode\": $input.json('$.statusCode'), \"message\": $input.json('$.message')}"
Type: MOCK
TimeoutInMillis: 29000
MethodResponses:
- ResponseModels:
application/json: !Ref ApiGatewayModel
StatusCode: 200
- ResponseModels:
application/json: !Ref ApiGatewayModel
StatusCode: 500
OperationName: 'mock'
ResourceId: !Ref ApiGatewayResource
RestApiId: !Ref ApiGatewayRestApi
ApiGatewayModel:
Type: AWS::ApiGateway::Model
Properties:
ContentType: 'application/json'
RestApiId: !Ref ApiGatewayRestApi
Schema: {}
ApiGatewayStage:
Type: AWS::ApiGateway::Stage
Properties:
DeploymentId: !Ref ApiGatewayDeployment
Description: Mock API Stage v0
RestApiId: !Ref ApiGatewayRestApi
StageName: 'v0'
ApiGatewayDeployment:
Type: AWS::ApiGateway::Deployment
DependsOn: ApiGatewayMethod
Properties:
Description: Mock API Deployment
RestApiId: !Ref ApiGatewayRestApi

Answer 2

To do this another way with SAM - i have
manually created a simple API gateway with a single GET and a mock response of static text in the integration response.
exported that with aws apigateway get-export
remove the servers and policy blocks (those i'll have in my sam template)
refer to the OAS spec in your SAM template in the API properties with DefinitionBody
upload the OAS spec
use SAM deploy
the SAM specifications.
For that approach thanks to valdeci for this answer, and Jens Eickmeyer for this post