Explain the difference between global and replicated service modes in Docker Swarm.

Explain the difference between global and replicated service modes in Docker Swarm.

In Docker Swarm, services can be deployed in either global mode or replicated mode, and the key difference lies in how tasks are distributed across the nodes in the Swarm.

  1. Global Service Mode:

    • In global mode, a service is deployed to every available node in the Swarm. It ensures that there is exactly one replica of the service running on each node.

    • This mode is suitable for services that should be highly available on every node and where each node should run an instance of the service.

Example command to deploy a service in global mode:

    docker service create --mode global --name my-service my-image
  1. Replicated Service Mode:

    • In replicated mode, the user specifies the desired number of replicas for a service. Docker Swarm then schedules and distributes those replicas across the available nodes in the Swarm.

    • Replicated mode is suitable for services that don't need to run on every node but need a specific number of instances running across the cluster.

Example command to deploy a service in replicated mode with 3 replicas:

    docker service create --mode replicated --replicas 3 --name my-service my-image

Summary:

  • Global mode ensures one replica per node, while replicated mode allows specifying the number of desired replicas.

  • Global mode is ideal for services that need to run on every node, ensuring high availability.

  • Replicated mode is suitable for scaling services to a specific number of replicas, distributing them across the nodes in the Swarm based on availability.

Understanding the differences between these modes allows users to choose the appropriate deployment strategy based on the requirements of their services.

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