To recall how to deploy a Swarm service, you might use a command like:

history | grep deploy

Here’s an example of a command to remove and deploy a Swarm service:

docker service rm homepage_homepage && docker stack deploy -c /home/facundo/homepage/docker-compose.yml homepage

The contents of the `docker-compose.yml` are as follows:

version: "3.3"
services:

  homepage:
    image: ghcr.io/gethomepage/homepage:latest
    restart: always
    ports:
      - 3080:3000
    volumes:
      - /mnt/swarm/homepage:/app/config # Make sure your local config directory exists
    deploy:
      replicas: 1
      restart_policy:
        condition: on-failure
      placement:
        constraints: [node.role != manager]

When you run the deployment command, you might see the following output:

Ignoring unsupported options: restart

Since --detach=false was not specified, tasks will be created in the background.
In a future release, --detach=false will become the default.
Creating service homepage_homepage

1. Command Breakdown

• `docker service rm homepage_homepage`:
  1. This command removes the existing service named `homepage_homepage`. This is useful to ensure a clean state before deploying the new service.

• `docker stack deploy -c /home/facundo/homepage/docker-compose.yml homepage`:
  1. This command deploys a stack using the specified Compose file (`docker-compose.yml`). The stack is named `homepage`.

2. YAML File Breakdown

version: "3.3" # Specifies the version of the Docker Compose file format

services: # Defines the services that make up the application

  homepage: # Name of the service
    image: ghcr.io/gethomepage/homepage:latest # Specifies the Docker image to use
    restart: always # This option is ignored in Swarm mode (only used in standalone Docker)
    ports:
      - 3080:3000 # Maps port 3080 on the host to port 3000 in the container
    volumes:
      - /mnt/swarm/homepage:/app/config # Mounts a volume from the host to the container
    deploy:
      replicas: 1 # Specifies the number of service replicas to run
      restart_policy:
        condition: on-failure # Defines the restart policy for failed tasks
      placement:
        constraints: [node.role != manager] # Ensures that the service runs only on worker nodes, not on the manager

3. Ignored Options and Output Explanation

• Ignoring unsupported options: restart:
  1. The `restart: always` option is used in standalone Docker configurations and is not supported in Swarm mode. In Swarm mode, restart policies are defined within the `deploy` section.

• Since –detach=false was not specified, tasks will be created in the background.:
  1. By default, `docker stack deploy` creates tasks in the background. This message indicates that the tasks are being created asynchronously. If you want to wait for the service to be fully deployed, you can use the `–detach=false` flag.

4. Why This Works

• Service Removal: By removing the existing service with `docker service rm`, you ensure that any previous configurations or issues are cleared before deploying the new service.

• Stack Deployment: The `docker stack deploy` command reads the specified Compose file and creates the defined services as part of a stack. It handles the deployment and orchestration of the services.

• YAML Configuration: The YAML file specifies the service details, including the image to use, port mappings, volume mounts, number of replicas, restart policy, and placement constraints. Docker Swarm uses this configuration to deploy and manage the service.

• Review Docker Swarm Documentation: Familiarize yourself with Docker Swarm concepts and commands. The official documentation is a great resource: [Docker Swarm Documentation](https://docs.docker.com/engine/swarm/).

• Monitoring and Logging: Consider setting up monitoring and logging for your Swarm services to keep track of their health and performance. Tools like Prometheus, Grafana, and the ELK stack (Elasticsearch, Logstash, Kibana) are popular choices.

• Backup and Recovery: Ensure that you have a backup strategy for your configurations and data. Regularly back up your volume mounts and configuration files.

• Security: Implement security best practices for your Docker Swarm setup, such as using secrets to manage sensitive data, setting resource limits, and ensuring your Docker daemon is securely configured.

I'd be happy to explain how this Docker Swarm deployment works and provide feedback. Let's break it down step by step:

First, here's the explanation in Dokuwiki syntax:

docker service rm homepage_homepage && docker stack deploy -c /home/facundo/homepage/docker-compose.yml homepage

• docker service rm homepage_homepage: This removes the existing service named “homepage_homepage”.
• &&: This operator ensures the next command runs only if the previous one succeeds.
• docker stack deploy: This command deploys a new stack or updates an existing stack.
  • -c /home/facundo/homepage/docker-compose.yml: Specifies the path to your Docker Compose file.
  • homepage: This is the name of your stack.

version: "3.3"
services:
  homepage:
    image: ghcr.io/gethomepage/homepage:latest
    restart: always
    ports:
      - 3080:3000
    volumes:
      - /mnt/swarm/homepage:/app/config
    deploy:
      replicas: 1
      restart_policy:
        condition: on-failure
      placement:
        constraints: [node.role != manager]

• version: “3.3”: Specifies the Docker Compose file version.
• services: Defines the services in your stack.
  • homepage: The name of your service.
    • image: The Docker image to use.
    • restart: always: Ignored in Swarm mode (as noted in the output).
    • ports: Maps port 3080 on the host to 3000 in the container.
    • volumes: Mounts a local directory to /app/config in the container.
    • deploy: Swarm-specific deployment options.
      • replicas: 1: Runs one instance of the service.
      • restart_policy: Defines when to restart the container.
      • placement: Ensures the service doesn't run on manager nodes.

1. The command first removes any existing service with the same name, ensuring a clean deployment.
2. It then deploys the stack using the specified Docker Compose file.
3. The Compose file defines how the service should be run, including its image, port mappings, and deployment constraints.
4. Swarm mode ignores certain Docker Compose options (like “restart”) that are not applicable in a clustered environment.

1. Consider using docker stack deploy without removing the service first. Swarm can usually update existing services smoothly.
2. If you frequently deploy, consider creating a shell script to streamline the process.
3. Use environment variables in your Compose file for values that might change between environments.

Ignoring unsupported options: restart

Since --detach=false was not specified, tasks will be created in the background.
In a future release, --detach=false will become the default.
Creating service homepage_homepage

1. The “restart” option is ignored because Swarm handles restarts differently.
2. The service is created in detached mode by default, running in the background.
3. The warning about “–detach=false” is informational for future Docker versions.