go-simple-websockets-chat-app

This is a golang implementation for the AWS example simple-websocket-chat-app. See https://github.com/aws-samples/simple-websockets-chat-app for the original implementation. There are three functions contained within the directories and a SAM template that wires them up to a DynamoDB table and provides the minimal set of permissions needed to run the app:

.
├── Makefile                    <-- Make to automate build
├── README.md                   <-- This instructions file
├── cmd
│   ├── connect
│   │   └── connect.go          <-- Lambda function code for connect
│   ├── disconnect
│   │   └── disconnect.go       <-- Lambda function code for disconnect
│   └── sendMessage
│       └── sendMessage.go      <-- Lambda function code for sendMessage
└── template.yaml               <-- SAM template for Lambda Functions and DDB

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 cmd/connect/connect ./cmd/connect/connect.go
	GOOS=linux GOARCH=amd64 go build -o cmd/disconnect/disconnect ./cmd/disconnect/disconnect.go
	GOOS=linux GOARCH=amd64 go build -o cmd/sendMessage/sendMessage ./cmd/sendMessage/sendMessage.go

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

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 go-simple-websockets-chat-app \
    --capabilities CAPABILITY_IAM

Testing

Install the wscat client.

npm install -g wscat

Now make a request to your depolyed API gateway

wscat -c wss://aabbccddee.execute-api.us-east-1.amazonaws.com/Prod/

This will present a terminal, where you can send messages that will be echo'd back. e.g.

connected (press CTRL+C to quit)
> {"message":"sendmessage", "data":"hello world"}
< {"message":"sendmessage", "data":"hello world"}

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 go-simple-websockets-chat-app \
    --query 'Stacks[].Outputs'

Appendix

Deleting Stack

aws cloudformation delete-stack --stack-name go-simple-websockets-chat-app

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