# Amazon API Gateway REST API using Mapping templates for status code and parameter mapping with Lambda integration The SAM template deploys an Amazon API Gateway REST API endpoint along with a mapping template integrated with a Lambda function. Using this, we can perform parameter mappings; override parameters after standard API Gateway mappings have been applied; conditionally map parameters based on body content or other parameter values; programmatically create new parameters on the fly; and override status codes returned by your integration endpoint. Any type of request parameter, response header, or response status code may be overridden. More information can be found at: https://docs.amazonaws.cn/en_us/apigateway/latest/developerguide/apigateway-override-request-response-parameters.html Note: when deploying this pattern, *CAPABILITY_IAM* is required. Learn more about this pattern at [Serverless Land Patterns](https://serverlessland.com/patterns/apigw-mappingtemplate-lambda) Important: this application uses various AWS services and there are costs associated with these services after the Free Tier usage - please see the [AWS Pricing page](https://aws.amazon.com/pricing/) for details. You are responsible for any AWS costs incurred. No warranty is implied in this example. ## Requirements * [Create an AWS account](https://portal.aws.amazon.com/gp/aws/developer/registration/index.html) if you do not already have one and log in. The IAM user that you use must have sufficient permissions to make necessary AWS service calls and manage AWS resources. * [AWS CLI](https://docs.aws.amazon.com/cli/latest/userguide/install-cliv2.html) installed and configured * [Git Installed](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git) * [AWS Serverless Application Model](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-install.html) (AWS SAM) installed ## Deployment Instructions 1. Create a new directory, navigate to that directory in a terminal and clone the GitHub repository: ``` git clone https://github.com/aws-samples/serverless-patterns ``` 2. Change directory to the pattern directory: ``` cd apigw-mappingtemplate-lambda ``` 3. From the command line, use AWS SAM to deploy the AWS resources for the pattern as specified in the template.yml file: ``` sam deploy --guided --capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM ``` 4. During the prompts: * Enter a stack name * Select the desired AWS Region * Allow SAM to create roles with the required permissions if needed. Once you have run guided mode once, you can use `sam deploy` in future to use these defaults. 5. Note the outputs from the SAM deployment process. These contain the resource names and/or ARNs which are used for testing. ## Testing The stack will output the **api endpoint**. You can use *Postman* or *curl* to send a POST request to the API Gateway endpoint. ``` curl -X POST 'https://abc.execute-api.ap-southeast-2.amazonaws.com/dev/' ``` Even though the Lambda function is returning a 200 statuscode explictly, and the API Gateway recieves a 200 status from Lambda acknowledging the successful invocation. However, due to the involvment of Mapping templates we receive (i.e., over-ride) the status as 400, status code as 650, and body error as 'changed' from the orginal 200, 200 and 'error1' respectively. ## Cleanup 1. Delete the stack ```bash sam delete ``` 2. Confirm the stack has been deleted ```bash aws cloudformation list-stacks --query "StackSummaries[?contains(StackName,'STACK_NAME')].StackStatus" ``` ---- Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved. SPDX-License-Identifier: MIT-0