API Gateway with CORS enabled for a Lambda proxy integration

This pattern creates an API Gateway REST API with Lambda proxy integration and CORS enabled.

Learn more about this pattern at Serverless Land Patterns: https://serverlessland.com/patterns/apigw-lambda-cors-proxy-sam-python

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 for details. You are responsible for any AWS costs incurred. No warranty is implied in this example.

Requirements

• Create an AWS account 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 installed and configured
• Git Installed
• AWS Serverless Application Model (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 _patterns-model
   

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
   

4. During the prompts:

   • Enter a stack name
   • Enter the desired AWS Region
   • Allow SAM CLI to create IAM roles with the required permissions.

   Once you have run sam deploy --guided mode once and saved arguments to a configuration file (samconfig.toml), 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.

How it works

A REST API is created that has a GET method with a Lambda non-proxy integration and an OPTIONS method with a Lambda proxy integration. CORS is enabled for both GET and OPTIONS method, but the headers 'Access-Control-Allow-Methods', 'Access-Control-Allow-Headers', 'Access-Control-Allow-Origin' are returned by the backend Lambda function for the OPTIONS method since it is a proxy integration."

Testing

Once you make requests to the API i.e. curl https://{api-id}.execute-api.{region}.amazonaws.com/prod/helloworld, you will receive a 'Hello from Lambda!' in response. You can test your API's CORS configuration by invoking your API, and checking the CORS headers in the response. The following curl command sends an OPTIONS request to a deployed API i.e. curl -v -X OPTIONS https://{api_id}.execute-api.{region}.amazonaws.com/prod/helloworld You can also use AWS SAM to view the logs, specifying the log group name, for example: sam logs --cw-log-group apigw-cors-proxy

Cleanup

1. Delete the stack

   aws cloudformation delete-stack --stack-name STACK_NAME

2. Confirm the stack has been deleted

   aws cloudformation list-stacks --query "StackSummaries[?contains(StackName,'STACK_NAME')].StackStatus"

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