Exploring the Hello World app

Hello World App Structure

To better understand what has been created and how these pieces glue together, let’s analyze whats each file of our sample app doing:

    ├── events                          <-- Folder for mock event payloads
    │   ├── event.json                  <-- Mock payload for local/unit testing
    ├── hello-world                     <-- source code of our function
    │   ├── tests                       <-- Parent folder for all tests
    │   │   ├── unit                    <-- Parent folder for all unit tests
    │   │   │   ├── test-handler.js     <-- Unit test for the lambda functions
    │   ├── app.js                      <-- Lambda function itself
    │   ├── package.json                <-- Node.js dependencies
    ├── template.yaml                   <-- SAM definition file

As we start thinking on how complex and big a microservice project can get, doesn’t this structure seem a lit bit too messy to manage in a real sized project? Why don’t we come up with our own best practices for our organization during this workshop?

SAM Template

When we are developing Serverless applications using AWS SAM, the template.yaml file becomes the heart of our application and specifies all resources that are to be provisioned.

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31 
Description: >

  Sample SAM Template for sample-app
# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
    Timeout: 3

    Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
      CodeUri: hello-world/
      Handler: app.lambdaHandler
      Runtime: nodejs12.x
          Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
            Path: /hello
            Method: get

  # ServerlessRestApi is an implicit API created out of Events key under Serverless::Function
  # Find out more about other implicit resources you can reference within SAM
  # https://github.com/awslabs/serverless-application-model/blob/master/docs/internals/generated_resources.rst#api
    Description: "API Gateway endpoint URL for Prod stage for Hello World function"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hello/"
    Description: "Hello World Lambda Function ARN"
    Value: !GetAtt HelloWorldFunction.Arn
    Description: "Implicit IAM Role created for Hello World function"
    Value: !GetAtt HelloWorldFunctionRole.Arn

As you can see, its syntax is extremely similar to AWS CloudFormation, except for the Globals sections which allows you to define global settings for AWS Lambda, Amazon API Gateway API’s and Amazon DynamoDB Tables, and the AWS::Serverless resources you can now create. To get started with SAM in your template, you have to add the Transform: AWS::Serverless-2016-10-31 clause in the beginning of your template.