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moby--moby/docs/swarm/index.md
Stephen J Day 0aa4e1e689
cli: docker service|node|stack ps instead of tasks 
Rather than conflict with the unexposed task model, change the names of
the object-oriented task display to `docker <object> ps`. The command
works identically to `docker service tasks`. This change is superficial.

This provides a more sensical docker experience while not trampling on
the task model that may be introduced as a top-level command at a later
date.

The following is an example of the display using `docker service ps`
with a service named `condescending_cori`:

```
$ docker service ps condescending_cori
ID                         NAME                  SERVICE             IMAGE   LAST STATE              DESIRED STATE  NODE
e2cd9vqb62qjk38lw65uoffd2  condescending_cori.1  condescending_cori  alpine  Running 13 minutes ago  Running        6c6d232a5d0e
```

The following shows the output for the node on which the command is
running:

```console
$ docker node ps self
ID                         NAME                  SERVICE             IMAGE   LAST STATE              DESIRED STATE  NODE
b1tpbi43k1ibevg2e94bmqo0s  mad_kalam.1           mad_kalam           apline  Accepted 2 seconds ago  Accepted       6c6d232a5d0e
e2cd9vqb62qjk38lw65uoffd2  condescending_cori.1  condescending_cori  alpine  Running 12 minutes ago  Running        6c6d232a5d0e
4x609m5o0qyn0kgpzvf0ad8x5  furious_davinci.1     furious_davinci     redis   Running 32 minutes ago  Running        6c6d232a5d0e
```

Signed-off-by: Stephen J Day <stephen.day@docker.com>
2016-07-27 11:06:42 -07:00

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Swarm mode overview

To use Docker Engine in swarm mode, install the Docker Engine v1.12.0-rc1 or later from the Docker releases GitHub repository. Alternatively, install the latest Docker for Mac or Docker for Windows Beta.

Docker Engine 1.12 includes swarm mode for natively managing a cluster of Docker Engines called a Swarm. Use the Docker CLI to create a swarm, deploy application services to a swarm, and manage swarm behavior.

If you’re using a Docker version prior to v1.12.0-rc1, see Docker Swarm.

Feature highlights

  • Cluster management integrated with Docker Engine: Use the Docker Engine CLI to create a Swarm of Docker Engines where you can deploy application services. You don't need additional orchestration software to create or manage a Swarm.

  • Decentralized design: Instead of handling differentiation between node roles at deployment time, the Docker Engine handles any specialization at runtime. You can deploy both kinds of nodes, managers and workers, using the Docker Engine. This means you can build an entire Swarm from a single disk image.

  • Declarative service model: Docker Engine uses a declarative approach to let you define the desired state of the various services in your application stack. For example, you might describe an application comprised of a web front end service with message queueing services and a database backend.

  • Scaling: For each service, you can declare the number of tasks you want to run. When you scale up or down, the swarm manager automatically adapts by adding or removing tasks to maintain the desired state.

  • Desired state reconciliation: The swarm manager node constantly monitors the cluster state and reconciles any differences between the actual state your expressed desired state. For example, if you set up a service to run 10 replicas of a container, and a worker machine hosting two of those replicas crashes, the manager will create two new replicas to replace the ones that crashed. The swarm manager assigns the new replicas to workers that are running and available.

  • Multi-host networking: You can specify an overlay network for your services. The swarm manager automatically assigns addresses to the containers on the overlay network when it initializes or updates the application.

  • Service discovery: Swarm manager nodes assign each service in the swarm a unique DNS name and load balances running containers. You can query every container running in the swarm through a DNS server embedded in the swarm.

  • Load balancing: You can expose the ports for services to an external load balancer. Internally, the swarm lets you specify how to distribute service containers between nodes.

  • Secure by default: Each node in the swarm enforces TLS mutual authentication and encryption to secure communications between itself and all other nodes. You have the option to use self-signed root certificates or certificates from a custom root CA.

  • Rolling updates: At rollout time you can apply service updates to nodes incrementally. The swarm manager lets you control the delay between service deployment to different sets of nodes. If anything goes wrong, you can roll-back a task to a previous version of the service.

What's next?