> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Demo Docker Stack

> This demonstrates how to deploy, verify, and scale services using Docker Stacks in a Swarm cluster.

In this lesson, we'll deploy the Example Voting App using Docker Stacks on a Swarm cluster. We start by upgrading our Compose file to version 3, deploy it as a stack, verify running services, and then scale the voting service.

## 1. Prepare the Docker Compose File (Version 3)

Below is the upgraded Compose file in version 3 format. Save this as `docker-stack.yml` on your Swarm manager:

```yaml theme={null}
version: '3'
services:
  redis:
    image: redis
  db:
    image: postgres:9.4
  vote:
    image: dockersamples/examplevotingapp_vote
    ports:
      - "5000:80"
  worker:
    image: dockersamples/examplevotingapp_worker
  result:
    image: dockersamples/examplevotingapp_result
    ports:
      - "5001:80"
```

The `dockersamples` images are available on Docker Hub.

<Frame>
  ![The image shows a Docker Hub profile page for "dockersamples," displaying a list of public repositories with details such as stars and pull counts.](https://kodekloud.com/kk-media/image/upload/v1752873922/notes-assets/images/Docker-Certified-Associate-Exam-Course-Demo-Docker-Stack/dockersamples-docker-hub-profile.jpg)
</Frame>

<Callout icon="lightbulb" color="#1CB2FE">
  Make sure Docker Swarm is initialized on your manager node:

  ```bash theme={null}
  docker swarm init
  ```
</Callout>

## 2. Deploy the Stack

1. SSH into your Swarm manager and create a project directory:
   ```bash theme={null}
   mkdir ~/voting-app-stack && cd ~/voting-app-stack
   ```
2. Place the `docker-stack.yml` file in this directory.
3. Deploy the stack:
   ```bash theme={null}
   docker stack deploy voting-app-stack --compose-file docker-stack.yml
   ```
   You should see output similar to:
   ```Docker Compose theme={null}
   Creating network voting-app-stack_default
   Creating service voting-app-stack_redis
   Creating service voting-app-stack_db
   Creating service voting-app-stack_vote
   Creating service voting-app-stack_worker
   Creating service voting-app-stack_result
   ```

Verify all services are up:

```bash theme={null}
docker service ls
```

| Service Name             | Replicas | Image                                         |
| ------------------------ | -------- | --------------------------------------------- |
| voting-app-stack\_redis  | 1/1      | redis:latest                                  |
| voting-app-stack\_db     | 1/1      | postgres:9.4                                  |
| voting-app-stack\_vote   | 1/1      | dockersamples/examplevotingapp\_vote:latest   |
| voting-app-stack\_worker | 0/1      | dockersamples/examplevotingapp\_worker:latest |
| voting-app-stack\_result | 1/1      | dockersamples/examplevotingapp\_result:latest |

## 3. Inspect Running Tasks

On any manager or worker node, list the active containers to ensure tasks are distributed:

```bash theme={null}
docker ps
```

Example output:

```text theme={null}
CONTAINER ID  IMAGE                                           NAMES
3940e228ce02  dockersamples/examplevotingapp_result:latest    voting-app-stack_result.1.abcde
9348d1d3d7f5  postgres:9.4                                    voting-app-stack_db.1.fghij
```

## 4. Access the Voting Application

Open a browser and navigate to:

* Voting interface: http\://\<manager-ip>:5000
* Results dashboard: http\://\<manager-ip>:5001

<Frame>
  ![The image shows a web page titled "Cats vs Dogs!" with options to vote for either "CATS" or "DOGS," and the "CATS" option is selected.](https://kodekloud.com/kk-media/image/upload/v1752873923/notes-assets/images/Docker-Certified-Associate-Exam-Course-Demo-Docker-Stack/cats-vs-dogs-vote-selected.jpg)
</Frame>

## 5. Scale the Voting Service

To handle higher traffic, update `docker-stack.yml` by adding the `deploy.replicas` setting under the `vote` service:

```yaml theme={null}
services:
  vote:
    image: dockersamples/examplevotingapp_vote
    ports:
      - "5000:80"
    deploy:
      replicas: 2
```

Redeploy the updated stack:

```bash theme={null}
docker stack deploy voting-app-stack --compose-file docker-stack.yml
```

Confirm that the voting service now has two replicas:

```bash theme={null}
docker service ls
```

| Service Name             | Replicas | Image                                         |
| ------------------------ | -------- | --------------------------------------------- |
| voting-app-stack\_vote   | 2/2      | dockersamples/examplevotingapp\_vote:latest   |
| voting-app-stack\_db     | 1/1      | postgres:9.4                                  |
| voting-app-stack\_redis  | 1/1      | redis:latest                                  |
| voting-app-stack\_result | 1/1      | dockersamples/examplevotingapp\_result:latest |
| voting-app-stack\_worker | 1/1      | dockersamples/examplevotingapp\_worker:latest |

Inspect each task:

```bash theme={null}
docker service ps voting-app-stack_vote
```

## Links and References

* [Docker Stack Deploy](https://docs.docker.com/engine/reference/commandline/stack_deploy/)
* [Docker Compose File Reference](https://docs.docker.com/compose/compose-file/)
* [Docker Swarm Overview](https://docs.docker.com/engine/swarm/)

This demonstrates how to deploy, verify, and scale services using Docker Stacks in a Swarm cluster.

<CardGroup>
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