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This is a sample template for hello-sam - Below is a brief explanation of what we have generated for you:

├──                   <-- This instructions file
├── hello_world                 <-- Source code for a lambda function
│   ├── app.js                  <-- Lambda function code
│   ├── package.json            <-- NodeJS dependencies
│   └── tests                   <-- Unit tests
│       └── unit
│           └── test_handler.js
└── template.yaml               <-- SAM template


Setup process

Installing dependencies

In this example we use npm but you can use yarn if you prefer to manage NodeJS dependencies:

cd hello_world
npm install
cd ../

Local development

Invoking function locally through local API Gateway

sam local start-api

If the previous command ran successfully you should now be able to hit the following local endpoint to invoke your function http://localhost:3000/hello

SAM CLI is used to emulate both Lambda and API Gateway locally and uses our template.yaml to understand how to bootstrap this environment (runtime, where the source code is, etc.) - The following excerpt is what the CLI will read in order to initialize an API and its routes:

        Type: Api # More info about API Event Source:
            Path: /hello
            Method: get

Packaging and deployment

AWS Lambda NodeJS runtime requires a flat folder with all dependencies including the application. SAM will use CodeUri property to know where to look up for both application and dependencies:

        Type: AWS::Serverless::Function
            CodeUri: hello_world/

Firstly, we need a S3 bucket where we can upload our Lambda functions packaged as ZIP before we deploy anything - If you don't have a S3 bucket to store code artifacts then this is a good time to create one:

aws s3 mb s3://BUCKET_NAME

Next, run the following command to package our Lambda function to S3:

sam package \
    --template-file template.yaml \
    --output-template-file packaged.yaml \

Next, the following command will create a Cloudformation Stack and deploy your SAM resources.

sam deploy \
    --template-file packaged.yaml \
    --stack-name hello-sam \
    --capabilities CAPABILITY_IAM

See Serverless Application Model (SAM) HOWTO Guide for more details in how to get started.

After deployment is complete you can run the following command to retrieve the API Gateway Endpoint URL:

aws cloudformation describe-stacks \
    --stack-name hello-sam \
    --query 'Stacks[].Outputs'


We use jest for testing our code and it is already added in package.json under scripts, so that we can simply run the following command to run our tests:

cd hello_world
npm run test


AWS CLI commands

AWS CLI commands to package, deploy and describe outputs defined within the cloudformation stack:

sam package \
    --template-file template.yaml \
    --output-template-file packaged.yaml \

sam deploy \
    --template-file packaged.yaml \
    --stack-name hello-sam \
    --capabilities CAPABILITY_IAM \
    --parameter-overrides MyParameterSample=MySampleValue

aws cloudformation describe-stacks \
    --stack-name hello-sam --query 'Stacks[].Outputs'

NOTE: Alternatively this could be part of package.json scripts section.

Bringing to the next level

Here are a few ideas that you can use to get more acquainted as to how this overall process works:

  • Create an additional API resource (e.g. /hello/{proxy+}) and return the name requested through this new path
  • Update unit test to capture that
  • Package & Deploy

Next, you can use the following resources to know more about beyond hello world samples and how others structure their Serverless applications:

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