How to Configure the Linux Firewall for Docker Swarm for Digital Ocean

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Docker Swarm is a feature of Docker that makes it easy to run Docker hosts and containers at scale. A Docker Swarm, or Docker cluster, is made up of one or more Dockerized hosts that function as manager nodes, and any number of worker nodes. Setting up such a system requires careful manipulation of the Linux firewall.

The network ports required for a Docker Swarm to function correctly are:

  • TCP port 2376 for secure Docker client communication. This port is required for Docker Machine to work. Docker Machine is used to orchestrate Docker hosts.
  • TCP port 2377. This port is used for communication between the nodes of a Docker Swarm or cluster. It only needs to be opened on manager nodes.
  • TCP and UDP port 7946 for communication among nodes (container network discovery).
  • UDP port 4789 for overlay network traffic (container ingress networking).

Commands

ufw allow 2377/tcp
ufw allow 7946/tcp
ufw allow 7946/udp
ufw allow 4789/udp

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