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Example Voting App

Architecture

Architecture diagram

  • A Python webapp which lets you vote between two options
  • A Redis queue which collects new votes
  • A .NET 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

Setup environment

Create required accounts

  1. Create a Microsoft Azure account.
  2. Create a Docker Hub account.

Install Git

  1. Install Git.

Install docker client

  1. Download the docker client, extract the files and copy docker.exe to a separate folder.
  2. Download docker-compose, rename it to docker-compose.exe and copy to the same folder.
  3. Add the folder containing the docker binaries to PATH.

Install Putty

Download Putty

Install azure-cli

  1. Download python.
  2. Run the installation, and add python-2.7.13.amd64 and python-2.7.13.amd64/Scripts to PATH.
  3. Run pip install azure-cli.
  4. Login into Azure by running az login and following the procedure.

Create a Docker host

To be able to run the application we need first to set up a remote docker host. Open Git bash and execute the following commands.

  1. Set a namespace variable to isolate your resources from others:
export NAMESPACE=<your name>
  1. Create a resource group:
az group create --name $NAMESPACE --location westeurope
  1. Create a Virtual Machine:
az vm create --resource-group $NAMESPACE --name $NAMESPACE-docker --image UbuntuLTS --admin-username dev --admin-password DockerDocker-1

Note the public IP of the VM. Also note the user name and the password. 4. Open the required ports on the VM:

az vm open-port -g $NAMESPACE -n $NAMESPACE-docker --port 80 --priority 900
az vm open-port -g $NAMESPACE -n $NAMESPACE-docker --port 2375 --priority 800
az vm open-port -g $NAMESPACE -n $NAMESPACE-docker --port 5000-5001 --priority 700
  1. SSH into the VM to install and run the Docker daemon:
sudo apt install aufs-tools docker.io
systemctl stop docker
sudo dockerd -H tcp://127.0.0.1:2375
  1. To verify the installation, on your local machine run:
export DOCKER_HOST=tcp://<ip address of the VM:2375
docker run hello-world

Run the application

  1. Clone the project:
git clone https://github.com/ctco-dev/example-voting-app.git
  1. Navigate to the project folder and run the application:
cd example-voting-app
docker-compose up

Wait until everything is downloaded.

The voting application will be available at http://<your VM's IP>:5000 and the result application at http://<your VM's IP>:5001.

Change the application

The next step would be to change the application from a cat-dog vote to a Java-Node vote.

  1. Stop the running application by pressing Ctrl+C.
  2. Open vote/app.py and replace all occurrences of Cats with Java and Dogs with Node. Do the same for result/views/index.html.
  3. Start the application by running:
docker-compose up --build

Note the --build argument.

Refresh the application in your browser and make sure, that the changes have been applied correctly.

Set up Redis and PostgreSQL on Azure

Setup Redis

  1. Create a Redis instance:
az redis create --location westeurope --name $NAMESPACE-redis --resource-group $NAMESPACE --sku Basic --vm-size C0

Note the value of the hostName property. 2. Retrieve the password to Redis:

az redis list-keys --name $NAMESPACE-redis --resource-group $NAMESPACE

Note the value of the primaryKey property. 3. Create a .env in the root of your project with the following contents:

REDIS_HOST=<host name>
REDIS_PASSWORD=<primary key>
REDIS_PORT=6380

Setup PostgreSQL

  1. Create a PostgreSQL instance:
az postgres server create --resource-group $NAMESPACE --name $NAMESPACE-postgresql  --location westeurope --admin-user dev --admin-password Postgres-1 --performance-tier Basic --compute-units 50 --version 9.6 --ssl-enforcement Disabled

Note the value of the fullyQualifiedDomainName and name properties. 2. Allow to connect from any IP:

az postgres server firewall-rule create -g $NAMESPACE -s $NAMESPACE-postgresql -n allowall --start-ip-address 0.0.0.0 --end-ip-address 255.255.255.255
  1. Add the following contents to your .env file:
POSTGRES_HOST=<your fullyQualifiedDomainName>
POSTGRES_USER=dev@<your instance name>
POSTGRES_PASSWORD=Postgres-1

Test

Restart your applications to verify the changes.

Publish the application

To deploy the applications to Azure we need to publish the images to Docker Hub first.

  1. Login into Docker Hub by running:
docker login

Enter your user name and password. 2. Create a docker-compose.override.yml file:

version: "3"

services:
  vote:
    image: <docker user name>/voting-app-vote

  result:
    image: <docker user name>/voting-app-result

  worker:
    image: <docker user name>/voting-app-worker
  1. Publish the images:
docker-compose push

Deploy the application

Now it's time to deploy the applications to Azure.

  1. Create a service plan:
az appservice plan create --name $NAMESPACE-asp --resource-group $NAMESPACE --sku S1 --is-linux
  1. Create three applications and configure the required settings:
az webapp create --resource-group $NAMESPACE --plan $NAMESPACE-asp --name $NAMESPACE-vote \
    --deployment-container-image-name <docker user>/voting-app-vote
az webapp config appsettings set -g $NAMESPACE -n $NAMESPACE-vote --settings \
    REDIS_HOST=<insert value from .env> \
    REDIS_PASSWORD=<insert value from .env> \
    REDIS_PORT=6380
az webapp config set -g $NAMESPACE -n $NAMESPACE-vote --always-on true

az webapp create --resource-group $NAMESPACE --plan $NAMESPACE-asp --name $NAMESPACE-result \
    --deployment-container-image-name <docker user>/voting-app-result
az webapp config appsettings set -g $NAMESPACE- -n $NAMESPACE-result --settings \
   POSTGRES_USER=<insert value from .env> \
   POSTGRES_PASSWORD=<insert value from .env>
az webapp config set -g $NAMESPACE -n $NAMESPACE-result --always-on true

az webapp create --resource-group $NAMESPACE --plan $NAMESPACE-asp --name $NAMESPACE-worker \
    --deployment-container-image-name <docker user>/voting-app-worker
az webapp config appsettings set -g $NAMESPACE -n $NAMESPACE-worker --settings \
    REDIS_HOST=<insert value from .env> \
    REDIS_PASSWORD=<insert value from .env> \
    REDIS_PORT=6380 \
    POSTGRES_HOST=<insert value from .env> \
    POSTGRES_USER=<insert value from .env> \
    POSTGRES_PASSWORD=<insert value from .env> \
    WEBSITES_CONTAINER_START_TIME_LIMIT=600
az webapp config set -g $NAMESPACE -n $NAMESPACE-worker --always-on true
  1. After some time the two frontend applications will be available at <namespace>-vote.azurewebsites.net and <namespace>-result.azurewebsites.net

Clean up resources

Once you're done playing around with your application, cleanup all of the resources you've created in Azure:

az group delete --name $NAMESPACE

Note

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