Joining Docker Swarm: Second Machine LAN Network Connection Refused

Title: Docker Swarm Second Machine LAN Network Connection Refused

Introduction

Docker Swarm is a powerful orchestration tool for managing containers across multiple hosts. However, when attempting to connect the second machine to the Docker Swarm network, you may encounter the error "connection refused". This article will provide a detailed context and cover the key concepts to help you resolve this issue.

Prerequisites

Before diving into the solution, ensure that both machines are connected to the same LAN network and have the latest version of Docker installed.

Steps to Connect Second Machine to Docker Swarm

1. Initialize Docker Swarm on the Manager Node

   On the manager node, run the following command to initialize the Docker Swarm:

   docker swarm init --advertise-addr MANAGER_IP
   

   Replace MANAGER_IP with the IP address of the manager node.

2. Join the Second Machine to the Docker Swarm

   On the worker node, run the following command to join the Docker Swarm:

   docker swarm join --token SWARM_TOKEN MANAGER_IP:2377
   

   Replace SWARM_TOKEN with the token generated during the initialization step.

Common Issues and Solutions

1. Incorrect IP Address

   Ensure that the MANAGER_IP used in the docker swarm init and docker swarm join commands is the correct IP address of the manager node.

2. Firewall Configuration

   Check if the firewall on the manager node is blocking the traffic from the worker node. Open ports 2375, 2376, and 2377 for TCP traffic on the manager node.

3. Docker Engine Configuration

   Verify that the Docker engine on the worker node is configured to use the correct Docker Swarm manager. Update the daemon.json file on the worker node with the following configuration:

   {
     "swarm": {
       "secrets": {},
       "default-addr": "tcp://MANAGER_IP:2377",
       "listen-addr": "0.0.0.0:2377"
     }
   }
   

   Replace MANAGER_IP with the IP address of the manager node.

4. Network Configuration

   If the machines are connected to different subnets, you may need to configure the network settings on both machines to allow communication.

Code Example

Assuming you have initialized the Docker Swarm on the manager node with IP address 192.168.1.100 and have generated the token SWARM_TOKEN.

On the manager node:

docker swarm init --advertise-addr 192.168.1.100

On the worker node:

docker swarm join --token SWARM_TOKEN 192.168.1.100:2377

Summary

• Ensure both machines are connected to the same LAN network.
• Run the docker swarm init command on the manager node and the docker swarm join command on the worker node.
• Check firewall, Docker engine, and network configurations on both machines.

References

• Docker Swarm: A Tutorial
• Docker Swarm Networking
• Docker Swarm Security
• Configure the Docker daemon
• Linux Firewall Commands