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Docker for Rails Developers

Visualizing Containers

Explore how to visualize containers running in a Docker Swarm cluster using a web-based visualizer tool. Learn to configure the visualizer service in your docker-stack.yml file, deploy it with placement constraints, and access its interface to monitor container scheduling across nodes in your cluster.

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Swarm’s orchestrator schedules containers (or more strictly, tasks to run containers) on whichever nodes it sees fit. That means we don’t know where a container for service will end up running.

Visualizer

For educational purposes, we are going to use a new “visualizer” tool that provides a web interface for seeing the nodes in our clusters, and the containers running on them. Docker provides a handy image for this. You wouldn’t typically run the visualizer in production, but it will give us a feel for how containers are scheduled across the cluster.

Modifying Stack file

Let’s add a visualizer service to our docker-stack.yml file:

YAML
visualizer:
  image: dockersamples/visualizer:stable
  ports:
	- "8080:8080"
  volumes:
    - "/var/run/docker.sock:/var/run/docker.sock"
  deploy:
    placement:
      constraints: [node.role == manager]

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