Setting up a sample voting app using Docker

Docker Sample Voting app is a distributed application which uses a Postgres database and Redis message queue, with application components running in Python, .NET and Node.js containers. All the components of the app are published in public images on Docker Hub.

Voting app

In this lab you’ll learn how to set up a sample voting app using Docker Swarm. You’ll gain experience of working with Docker Compose and Docker Swarm

Init your swarm

Let’s create a Docker Swarm first. Open up the first instance and initiate Swarm mode cluster.

docker swarm init --advertise-addr $(hostname -i)

This node becomes a manager node. The output displays a command to add a worker node to this swarm as shown below:

Swarm initialized: current node (xf323rkhg80qy2pywkjkxqusp) is now a manager.

To add a worker to this swarm, run the following command:

    docker swarm join --token SWMTKN-1-41uv2d4keynz33b5z9nozygzfai4gpu7ufk33347i2vgfgtu1h-1vizoglo6pwz9w4hugim46ayl 192.168.0.18:2377

To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.

The above token ID is unique for every swarm mode cluster and hence might differ for your setup. From the output above, copy the join command (watch out for newlines).

Next, Open up the new instance and paste the below command. This should join the new node to the swarm mode cluster and this new node becomes a worker node. In my case, the command would look something like this:

 docker swarm join \
    --token SWMTKN-1-089phhmfamjor1o1qj8s0l4wdhyvegphg6vtt9p3s8c35upltk-eecvhhtz1f2vpjhvc70v6v
vzb \
    10.0.50.3:2377

Output:

$ docker swarm join --token SWMTKN-1-089phhmfamjor1o1qj8s0l4wdhyvegphg6vtt9p3s8c35upltk-eecvhh
tz1f2vpjhvc70v6vvzb 10.0.50.3:2377
This node joined a swarm as a worker.

Show members of swarm

Type the below command in the first terminal:

docker node ls

The output shows you both the manager and worker node indicating 2-node cluster:

ID                           HOSTNAME  STATUS  AVAILABILITY  MANAGER STATUS
xf323rkhg80qy2pywkjkxqusp *  node1     Ready   Active        Leader
za75md1p0hpc2qswefj8uyktk    node2     Ready   Active

2. Cloning the repository

The source code repo for the sample voting app includes a Docker Compose file to bring up required microservices. Start by cloning the repo:

git clone https://github.com/dockersamples/example-voting-app && cd example-voting-app

3. Running Voting App Compose file

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

4. Verifying the services

docker service ls

Wait for few seconds. Open up Swarm Visualizer tool

5. Accessing the voting app

The vote interface is then available on port 5000.

Click here to access the voting app

Voting app

6. Accessing the results

The vote interface results is then available on port 5001. Click here to access the results

Voting app

How does it work?

A front-end web app in Python or ASP.NET Core which lets you vote between two options
A Redis or NATS queue which collects new votes
A .NET Core, Java or .NET Core 2.1 worker which consumes votes and stores them in…
A Postgres or TiDB database backed by a Docker volume
A Node.js or ASP.NET Core SignalR webapp which shows the results of the voting in real time