Getting started with Swarm mode

Table of contents

This tutorial introduces you to the features of Docker Engine Swarm mode. You may want to familiarize yourself with the key concepts before you begin.

The tutorial guides you through:

  • Initializing a cluster of Docker Engines in swarm mode
  • Adding nodes to the swarm
  • Deploying application services to the swarm
  • Managing the swarm once you have everything running

This tutorial uses Docker Engine CLI commands entered on the command line of a terminal window.

If you are brand new to Docker, see About Docker Engine.

Set up

To run this tutorial, you need:

Three networked host machines

This tutorial requires three Linux hosts which have Docker installed and can communicate over a network. These can be physical machines, virtual machines, Amazon EC2 instances, or hosted in some other way. Check out Deploy to Swarm for one possible set-up for the hosts.

One of these machines is a manager (called manager1) and two of them are workers (worker1 and worker2).

Note

You can follow many of the tutorial steps to test single-node swarm as well, in which case you need only one host. Multi-node commands do not work, but you can initialize a swarm, create services, and scale them.

Install Docker Engine on Linux machines

If you are using Linux based physical computers or cloud-provided computers as hosts, simply follow the Linux install instructions for your platform. Spin up the three machines, and you are ready. You can test both single-node and multi-node swarm scenarios on Linux machines.

The IP address of the manager machine

The IP address must be assigned to a network interface available to the host operating system. All nodes in the swarm need to connect to the manager at the IP address.

Because other nodes contact the manager node on its IP address, you should use a fixed IP address.

You can run ifconfig on Linux or macOS to see a list of the available network interfaces.

The tutorial uses manager1 : 192.168.99.100.

Open protocols and ports between the hosts

The following ports must be available. On some systems, these ports are open by default.

  • Port 2377 TCP for communication with and between manager nodes
  • Port 7946 TCP/UDP for overlay network node discovery
  • Port 4789 UDP (configurable) for overlay network traffic

If you plan on creating an overlay network with encryption (--opt encrypted), you also need to ensure IP protocol 50 (IPSec ESP) traffic is allowed.

Port 4789 is the default value for the Swarm data path port, also known as the VXLAN port. It is important to prevent any untrusted traffic from reaching this port, as VXLAN does not provide authentication. This port should only be opened to a trusted network, and never at a perimeter firewall.

If the network which Swarm traffic traverses is not fully trusted, it is strongly suggested that encrypted overlay networks be used. If encrypted overlay networks are in exclusive use, some additional hardening is suggested:

# Example iptables rule (order and other tools may require customization)
iptables -I INPUT -m udp --dport 4789 -m policy --dir in --pol none -j DROP

Next steps

Next, you'll create a swarm.

Create a swarm