sam-app

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

.
├── Makefile                    <-- Make to automate build
├── README.md                   <-- This instructions file
├── hello-world                 <-- Source code for a lambda function
│   ├── main.go                 <-- Lambda function code
│   └── main_test.go            <-- Unit tests
└── template.yaml

Requirements

• AWS CLI already configured with Administrator permission
• Docker installed
• Golang

Setup process

Installing dependencies

In this example we use the built-in go get and the only dependency we need is AWS Lambda Go SDK:

go get -u github.com/aws/aws-lambda-go/...

NOTE: As you change your application code as well as dependencies during development, you might want to research how to handle dependencies in Golang at scale.

Building

Golang is a statically compiled language, meaning that in order to run it you have to build the executable target.

You can issue the following command in a shell to build it:

GOOS=linux GOARCH=amd64 go build -o hello-world/hello-world ./hello-world

NOTE: If you're not building the function on a Linux machine, you will need to specify the GOOS and GOARCH environment variables, this allows Golang to build your function for another system architecture and ensure compatibility.

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:

...
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

Packaging and deployment

AWS Lambda Python 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:

...
    FirstFunction:
        Type: AWS::Serverless::Function
        Properties:
            CodeUri: hello_world/
            ...

First and foremost, 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 \
    --output-template-file packaged.yaml \
    --s3-bucket REPLACE_THIS_WITH_YOUR_S3_BUCKET_NAME

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

sam deploy \
    --template-file packaged.yaml \
    --stack-name sam-app \
    --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 sam-app \
    --query 'Stacks[].Outputs'

Testing

We use testing package that is built-in in Golang and you can simply run the following command to run our tests:

go test -v ./hello-world/

Appendix

Golang installation

Please ensure Go 1.x (where 'x' is the latest version) is installed as per the instructions on the official golang website: https://golang.org/doc/install

A quickstart way would be to use Homebrew, chocolatey or your linux package manager.

Homebrew (Mac)

Issue the following command from the terminal:

brew install golang

If it's already installed, run the following command to ensure it's the latest version:

brew update
brew upgrade golang

Chocolatey (Windows)

Issue the following command from the powershell:

choco install golang

If it's already installed, run the following command to ensure it's the latest version:

choco upgrade golang

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 \
    --s3-bucket REPLACE_THIS_WITH_YOUR_S3_BUCKET_NAME

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

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

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:

• AWS Serverless Application Repository