How to get Swarm

How to get Docker Swarm

You can create a Docker Swarm cluster using the swarm executable image from a container or using an executable swarm binary you install on your system. This page introduces the two methods and discusses their pros and cons.

Create a cluster with an interactive container

You can use the Docker Swarm official image to create a cluster. The image is built by Docker and updated regularly through an automated build. To use the image, you run it a container via the Engine docker run command. The image has multiple options and subcommands you can use to create and manage a Swarm cluster.

The first time you use any image, Docker Engine checks to see if you already have the image in your environment. By default Docker runs the swarm:latest version but you can also specify a tag other than latest. If you have an image locally but a newer one exists on Docker Hub, Engine downloads it.

Run the Swarm image from a container

1. Open a terminal on a host running Engine.

   If you are using Mac or Windows, then you must make sure you have started a Docker Engine host running and pointed your terminal environment to it with the Docker Machine commands. If you aren’t sure, you can verify:

   $ docker-machine ls
   NAME      ACTIVE   URL          STATE     URL                         SWARM   DOCKER    ERRORS
   default   *       virtualbox   Running   tcp://192.168.99.100:2376           v1.9.1    
   

   This shows an environment running an Engine host on the default instance.

2. Use the swarm image to execute a command.

   The easiest command is to get the help for the image. This command shows all the options that are available with the image.

   $ docker run swarm --help
   Unable to find image 'swarm:latest' locally
   latest: Pulling from library/swarm
   d681c900c6e3: Pull complete
   188de6f24f3f: Pull complete
   90b2ffb8d338: Pull complete
   237af4efea94: Pull complete
   3b3fc6f62107: Pull complete
   7e6c9135b308: Pull complete
   986340ab62f0: Pull complete
   a9975e2cc0a3: Pull complete
   Digest: sha256:c21fd414b0488637b1f05f13a59b032a3f9da5d818d31da1a4ca98a84c0c781b
   Status: Downloaded newer image for swarm:latest
   Usage: swarm [OPTIONS] COMMAND [arg...]
   
   A Docker-native clustering system
   
   Version: 1.0.1 (744e3a3)
   
   Options:
     --debug           debug mode [$DEBUG]
     --log-level, -l "info"    Log level (options: debug, info, warn, error, fatal, panic)
     --help, -h            show help
     --version, -v         print the version
   
   Commands:
     create, c Create a cluster
     list, l   List nodes in a cluster
     manage, m Manage a docker cluster
     join, j   join a docker cluster
     help, h   Shows a list of commands or help for one command
   
   Run 'swarm COMMAND --help' for more information on a command.
   

   In this example, the swarm image did not exist on the Engine host, so the Engine downloaded it. After it downloaded, the image executed the help subcommand to display the help text. After displaying the help, the swarm image exits and returns you to your terminal command line.

3. List the running containers on your Engine host.

   $ docker ps
   CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
   

   Swarm is no longer running. The swarm image exits after you issue it a command.

Why use the image?

Using a Swarm container has three key benefits over other methods:

• You don’t need to install a binary on the system to use the image.
• The single command docker run command gets and run the most recent version of the image every time.
• The container isolates Swarm from your host environment. You don’t need to perform or maintain shell paths and environments.

Running the Swarm image is the recommended way to create and manage your Swarm cluster. All of Docker’s documentation and tutorials use this method.

Run a Swarm binary

Before you run a Swarm binary directly on a host operating system (OS), you compile the binary from the source code or get a trusted copy from another location. Then you run the Swarm binary.

To compile Swarm from source code, refer to the instructions in CONTRIBUTING.md.

Why use the binary?

Using a Swarm binary this way has one key benefit over other methods: If you are a developer who contributes to the Swarm project, you can test your code changes without “containerizing” the binary before you run it.

Running a Swarm binary on the host OS has disadvantages:

• Compilation from source is a burden.
• The binary doesn’t have the benefits that Docker containers provide, such as isolation.
• Most Docker documentation and tutorials don’t show this method of running swarm.

Lastly, because the Swarm nodes don’t use Engine, you can’t use Docker-based software tools, such as Docker Engine CLI at the node level.

Related information

• Docker Swarm official image repository on Docker Hub
• Provision a Swarm with Docker Machine