Letterbox

An MMO typing simulator to demonstrate working with Docker and Kubernetes.

Letterbox provides a 80x24 textbox where users can type and see others while they type, in real time.

A presentation was done featuring Letterbox as a sample application, see under talk/.

Features

• Persist history
• Calculate snapshots to avoid recalculating years of small changes
• Horizontally scalable, events are broadcast via RabbitMQ
• Realtime updates to clients via WebSockets
• Uses Vanilla JS

Building

Letterbox uses Webpack to bundle its frontend code, which you can do by running:

npm run build

Running

Development

Letterbox requires MySQL and RabbitMQ to be running and configured. You can use .sh files under scripts/ to start them in Docker containers.

./scripts/start-docker-mysql.sh
./scripts/start-docker-rabbitmq.sh

Note: The MySQL database needs to be setup before running the application. You can either do this manually by using the PHPMyAdmin interface started by the script and copy the contents of scripts/database-setup.sql, or change the shell script to use the elementbound/letterbox-db image.

Next, configure Letterbox based on the .env.example file.

Once you are done, you can run Letterbox:

npm run start:dev

As you edit the backend code, the application will restart. Editing frontend code will trigger Webpack to rebuild the frontend bundle.

You can open Letterbox at http://localhost:3000/.

Locally

If you want to just see the application running, you can use Docker Compose:

docker-compose up

This will launch the application and all of its dependencies and should be up and running in a matter of seconds. You can open the application at http://localhost:3000/.

In Kubernetes

Aside from secrets, all resource descriptors are stored under kube/.

First, you'll need to create the namespaces:

kubectl apply -f kube/letterbox-namespace.yml
kubectl apply -f kube/letterbox-mq-namespace.yml

Prepare the secrets needed for RabbitMQ, in the letterbox-mq namespace:

Name	Contents
erlang-cookie	cookie=xleqtnracuavhilawxjecnttmtfanbrs
rabbitmq-admin	user=letterbox
	pass=vrlpvtrsefadeqof

Then create the RabbitMQ deployment:

kubectl apply -f kube/rabbitmq

Next, prepare the secrets for letterbox, in the letterbox namespace:

Name	Contents
letterbox-db-root	MYSQL_ROOT_PASSWORD=gcnfwtsstnpmhfwb
	DATABASE_PASSWORD=gcnfwtsstnpmhfwb
	DATABASE_USER=root
letterbox-mq-secret	url=amqp://letterbox:vrlpvtrsefadeqof@rabbitmq-client.letterbox-mq.svc.cluster.local:5672

Once done, create letterbox in the cluster:

kubectl apply -f kube

Once done, you should have a fully functioning letterbox deployment behind a loadbalancer. Use the loadbalancer's external IP to access your very own letterbox.

License

Unless otherwise noted, the contents of this repository are under the MIT license.

See LICENSE.