AWS SAM reference architecture with layers and shared local code

This project contains source code and supporting files for a serverless application that you can deploy with the SAM CLI. It includes the following files and folders.

• lambdas - Code for the application's Lambda functions.
• events - Invocation events that you can use to invoke the function.
• lambdas/*/tests - Unit tests for the application code.
• template.yaml - A template that defines the application's AWS resources.

The application uses several AWS resources, including Lambda functions, Layers, and an API Gateway API. These resources are defined in the template.yaml file in this project. You can update the template to add AWS resources through the same deployment process that updates your application code.

Deploy the sample application

The Serverless Application Model Command Line Interface (SAM CLI) is an extension of the AWS CLI that adds functionality for building and testing Lambda applications. It uses Docker to run your functions in an Amazon Linux environment that matches Lambda. It can also emulate your application's build environment and API.

To use the SAM CLI, you need the following tools.

• SAM CLI - Install the SAM CLI
• Node.js - Install Node.js 10, including the NPM package management tool.
• Docker - Install Docker community edition

To build and deploy your application for the first time, run the following in your shell:

sam build
sam deploy --guided

The first command will build the source of your application. The second command will package and deploy your application to AWS, with a series of prompts:

• Stack Name: The name of the stack to deploy to CloudFormation. This should be unique to your account and region, and a good starting point would be something matching your project name.
• AWS Region: The AWS region you want to deploy your app to.
• Confirm changes before deploy: If set to yes, any change sets will be shown to you before execution for manual review. If set to no, the AWS SAM CLI will automatically deploy application changes.
• Allow SAM CLI IAM role creation: Many AWS SAM templates, including this example, create AWS IAM roles required for the AWS Lambda function(s) included to access AWS services. By default, these are scoped down to minimum required permissions. To deploy an AWS CloudFormation stack which creates or modified IAM roles, the CAPABILITY_IAM value for capabilities must be provided. If permission isn't provided through this prompt, to deploy this example you must explicitly pass --capabilities CAPABILITY_IAM to the sam deploy command.
• Save arguments to samconfig.toml: If set to yes, your choices will be saved to a configuration file inside the project, so that in the future you can just re-run sam deploy without parameters to deploy changes to your application.

You can find your API Gateway Endpoint URL in the output values displayed after deployment.

Use the SAM CLI to build and test locally

Build your application with the sam build command.

aws-sam-layers-template$ sam build

The SAM CLI installs dependencies defined in each of the lambda function folders using each's package.json, creates a deployment package, and saves it in the .aws-sam/build folder.

Test a single function by invoking it directly with a test event. An event is a JSON document that represents the input that the function receives from the event source. Test events are included in the events folder in this project.

Run functions locally and invoke them with the sam local invoke command.

aws-sam-layers-template$ sam local invoke Func1 --event events/event.json
aws-sam-layers-template$ sam local invoke Func2 --event events/event.json

The SAM CLI can also emulate your application's API. Use the sam local start-api to run the API locally on port 3000.

aws-sam-layers-template$ sam local start-api
aws-sam-layers-template$ curl http://localhost:3000/func1
aws-sam-layers-template$ curl http://localhost:3000/func2

Debugging your lambda functions

Run one of the following commands.

aws-sam-layers-template$ sam local invoke Func1 --debug-port 5858 --event events/event.json
aws-sam-layers-template$ sam local invoke Func2 --debug-port 5858 --event events/event.json
aws-sam-layers-template$ sam local start-api --debug-port 5858

The above commands are also available via npm scripts:

aws-sam-layers-template$ npm run debug:func1
aws-sam-layers-template$ npm run debug:func2
aws-sam-layers-template$ npm run debug:api

Once the local invoke is ready, you can attach the debugger by going to the debug tab in VS Code, selecting Attach to Func1 or Attach to Func2, and clicking the play button. You will want to have a breakpoint set. When it hits your breakpoint, you should be able to debug the code.

If you're trying to debug using the api, then you'll have to trigger the event through a web browser (http://localhost:3000/func2) and attach using one of the attach commands Attach to Func1 or Attach to Func2.

Add a resource to your application

The application template uses AWS Serverless Application Model (AWS SAM) to define application resources. AWS SAM is an extension of AWS CloudFormation with a simpler syntax for configuring common serverless application resources such as functions, triggers, and APIs. For resources not included in the SAM specification, you can use standard AWS CloudFormation resource types.

Fetch, tail, and filter Lambda function logs

To simplify troubleshooting, SAM CLI has a command called sam logs. sam logs lets you fetch logs generated by your deployed Lambda function from the command line. In addition to printing the logs on the terminal, this command has several nifty features to help you quickly find the bug.

NOTE: This command works for all AWS Lambda functions; not just the ones you deploy using SAM.

aws-sam-layers-template$ sam logs -n Func1 --stack-name aws-sam-layers-template --tail
aws-sam-layers-template$ sam logs -n Func2 --stack-name aws-sam-layers-template --tail

Unit tests

Tests are defined in the lambdas/*/tests folders in this project. Use NPM to install the Mocha test framework and run unit tests.

aws-sam-layers-template$ npm run test

Cleanup

To delete the sample application that you created, use the AWS CLI. Assuming you used your project name for the stack name, you can run the following:

aws cloudformation delete-stack --stack-name aws-sam-layers-template

Resources

See the AWS SAM developer guide for an introduction to SAM specification, the SAM CLI, and serverless application concepts.

Next, you can use AWS Serverless Application Repository to deploy ready to use Apps that go beyond hello world samples and learn how authors developed their applications: AWS Serverless Application Repository main page