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Setup for voting app example
multi-container, services, swarm mode, cluster, voting app, docker-stack.yml, docker stack deploy
Try it out and vote

Now that the app is up and running, let's try it out.

We will vote for cats and dogs, view the results, and monitor the manager and worker nodes, containers and services on a visualizer.

Vote for cats and dogs

Go to <MANAGER-IP>:5000 in a web browser to view the voting page from a user perspective.

Voting web page

Click on either cats or dogs to vote.

View the results tally

Now, go to <MANAGER-IP>:5001 in a web browser to view the voting results tally, as one might do in the role of poll coordinator. The tally is shown by percentage in the current configuration of the app. (The voting app sample accepts only one vote per client, so you won't be able to see your multiple votes.)

Results web page

Tip: To get the IP address of the manager, open a terminal window that is not ssh'ed into a virtual machine (or exit out of a current one), and type either docker-machine ip manager or docker-machine ls. Look back at Verify machines are running and get IP addresses) for examples.

Use the visualizer to monitor the app

Go to <MANAGER-IP>:8080 to get a visual map of how the application is deployed.

Visualizer web page

This surfaces some configuration and characteristics from docker-stack.yml, and you can see those strategies in action here. For example:

  • We have two nodes running: a manager and a worker.

  • The manager node is running the PostgreSQL container, as configured by setting [node.role == manager] as a constraint in the deploy key for the db service. This service must be constrained to run on the manager in order to work properly.

    node role manager

  • The manager node is also running the visualizer itself, as configured by setting [node.role == manager] as a constraint in the deploy key for the visualizer service. This service must be constrained to run on the manager in order to work properly. If you remove the constraint, and it ends up on a worker, the web page display will be blank.

    visualizer role manager

  • Two of the services are replicated:

    • vote (represented in the visualizer by vote_vote)
    • redis (represented in the visualizer by vote_redis)

    Both of these services are configured as replicas: 2 under the deploy key. In the current state of this app (shown in the visualizer), one of each of these containers is running on a manager and on a worker. However, since neither are explicitly constrained to either node in docker-stack.yml, all or some of these services could be running on either node, depending on workload and re-balancing choices we've left to the swarm orchestration.

    replicas

What's next?

In the next steps, we'll customize the app and redeploy it.