To better understand what has been created and how these pieces glue together, let’s analyze whats each file of our sample app doing:
sample-app
├── 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?
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-app
Sample SAM Template for sample-app
# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
Globals:
Function:
Timeout: 3
Resources:
HelloWorldFunction:
Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
Properties:
CodeUri: hello-world/
Handler: app.lambdaHandler
Runtime: nodejs12.x
Events:
HelloWorld:
Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
Properties:
Path: /hello
Method: get
Outputs:
# 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
HelloWorldApi:
Description: "API Gateway endpoint URL for Prod stage for Hello World function"
Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hello/"
HelloWorldFunction:
Description: "Hello World Lambda Function ARN"
Value: !GetAtt HelloWorldFunction.Arn
HelloWorldFunctionIamRole:
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.