instruction: Create a Dockerfile for cluster
output: ```dockerfile
  from manager nodes.
  By default manager nodes also run services as worker nodes, but you can
  configure them to run manager tasks exclusively and be manager-only
  nodes. An agent runs on each worker node and reports on the tasks assigned to
  it. The worker node notifies the manager node of the current state of its
  assigned tasks so that the manager can maintain the desired state of each
  worker.Services and tasksA service is the definition of the tasks to execute on the manager or worker nodes. It
  is the central structure of the swarm system and the primary root of user
  interaction with the swarm.When you create a service, you specify which container image to use and which
  commands to execute inside running containers.In the replicated services model, the swarm manager distributes a specific
  number of replica tasks among the nodes based upon the scale you set in the
  desired state.For global services, the swarm runs one task for the service on every
  available node in the cluster.A task carries a Docker container and the commands to run inside the
  container. It is the atomic scheduling unit of swarm. Manager nodes assign tasks
  to worker nodes according to the number of replicas set in the service scale.
  Once a task is assigned to a node, it cannot move to another node. It can only
  run on the assigned node or fail.Load balancingThe swarm manager uses ingress load balancing to expose the services you
  want to make available externally to the swarm. The swarm manager can
  automatically assign the service a published port or you can configure a
  published port for the service. You can specify any unused port. If you do not
  specify a port, the swarm manager assigns the service a port in the 30000-32767
  range.External components, such as cloud load balancers, can access the service on the
  published port of any node in the cluster whether or not the node is currently
  running the task for the service. All nodes in the swarm route ingress
  connections to a running task instance.Swarm mode has an internal DNS component that automatically assigns each service
  in the swarm a DNS entry. The swarm manager uses internal load balancing to
  distribute requests among services within the cluster based upon the DNS name of
  the service.What's next?Read the Swarm mode overview.Get started with the Swarm mode tutorial.
  Request changesTable of contentsWhat is a swarm?NodesServices and tasksLoad balancingWhat's next?
  
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