Example Voting App

A simple distributed application running across multiple Docker containers.

Getting started

Download Docker Desktop for Mac or Windows. Docker Compose will be automatically installed. On Linux, make sure you have the latest version of Compose.

Linux Containers

The Linux stack uses Python, Node.js, and Java, with Redis for messaging and Postgres for storage.

Run in this directory:

docker-compose up

The app will be running at http://localhost:5000, and the results will be at http://localhost:5001.

Alternately, if you want to run it on a Docker Swarm, first make sure you have a swarm. If you don't, run:

docker swarm init

Once you have your swarm, in this directory run:

docker stack deploy --compose-file docker-stack.yml vote

Run the app in Kubernetes

The folder k8s-manifest contains the resources of the Voting App's services.

First create the vote namespace

kubectl create namespace vote

Run the following command to create the deployments and services objects:

$ kubectl apply -f k8s-manifests/
deployment "db" created
service "db" created
deployment "redis" created
service "redis" created
deployment "result" created
service "result" created
deployment "vote" created
service "vote" created
deployment "worker" created

The vote interface is then available on port 31000 on each host of the cluster, the result one is available on port 31001.

Architecture

• A frontend web app in Python which lets you vote between two options
• A Redis queue which collects new votes
• A Java worker which consumes votes and stores them in…
• A Postgres database backed by a Docker volume
• A Node.js webapp which shows the results of the voting in real time

Notes

The voting application only accepts one vote per client. It does not register votes if a vote has already been submitted from a client.

This isn't an example of a properly architected perfectly designed distributed app... it's just a simple example of the various types of pieces and languages you might see (queues, persistent data, etc), and how to deal with them in Docker at a basic level.