2 dockers installed on ubuntu server

Daniel Parker

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01-03-2025

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Running Two Docker Instances on Ubuntu Server: A Comprehensive Guide

This guide explains how to install and manage two separate Docker instances on a single Ubuntu server. This might be necessary for various reasons, such as isolating environments for different projects, experimenting with different Docker versions, or separating production and development workflows. We'll focus on achieving this using different user accounts and distinct configuration directories.

H1: Setting Up the First Docker Instance

This section details the initial Docker installation, assuming you're familiar with basic Ubuntu server administration.

H2: Standard Docker Installation

1. Update the system: Begin by updating your Ubuntu repositories: sudo apt update && sudo apt upgrade -y

2. Install prerequisites: Docker requires some dependencies. Install them using: sudo apt install \ apt-transport-https \ ca-certificates \ curl \ gnupg \ lsb-release

3. Add Docker's GPG key: This verifies the authenticity of the Docker packages: curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

4. Set up the repository: Add the Docker repository to your system: echo \ "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \ $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

5. Update and install Docker Engine: Now update your package lists and install Docker: sudo apt update && sudo apt install docker-ce docker-ce-cli containerd.io docker-compose-plugin

6. Add your user to the docker group: This allows you to run Docker commands without sudo: sudo usermod -aG docker $USER && newgrp docker

H1: Installing the Second Docker Instance

This is where we diverge from the standard installation. We'll use a separate user account and a custom Docker installation directory.

H2: Creating a Separate User Account

1. Create a new user: Use a user name that clearly distinguishes this Docker instance (e.g., docker2). sudo adduser docker2

2. Set a strong password: sudo passwd docker2

H2: Installing Docker for the Second User

We'll repeat the Docker installation steps, but within the new user's home directory and with custom paths. We'll utilize dockerd directly, offering more control.

1. Switch to the new user: su - docker2

2. Create a custom directory structure: This prevents conflicts with the first Docker instance. Make directories for Docker data and configuration: mkdir -p ~/.docker/data ~/.docker/config

3. Download Docker: Download the appropriate Docker binary for your architecture (replace <arch> with amd64 or arm64 as needed): curl -LO https://download.docker.com/linux/ubuntu/docker-ce-<version>.<arch>.tar.gz (Replace <version> with the desired version.)

4. Extract Docker: tar -xzf docker-ce-<version>.<arch>.tar.gz

5. Copy Docker files: Copy the necessary files into the custom directory (adjust paths as needed): cp docker/* ~/.docker/data/

6. Configure Docker (daemon.json): Create a daemon.json file within ~/.docker/config:

{
  "data-root": "~/.docker/data",
  "storage-driver": "overlay2"  // or your preferred driver
}

7. Run Docker: Start the Docker daemon using: ~/.docker/data/dockerd -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2375 (Note: Exposing Docker on 0.0.0.0:2375 is generally insecure; use only on private networks or with appropriate security measures. Consider using a dedicated socket path instead of unix:///var/run/docker.sock for enhanced security.)

H1: Managing Multiple Docker Instances

Now that you have two Docker instances running, here's how to manage them.

H2: Accessing Each Instance

• First Instance: Use standard Docker commands as the root user or your initial user (after adding to the docker group).

• Second Instance: Log in as the docker2 user and use Docker commands from within their home directory. Because we configured a different socket location, you might need to specify it in your Docker commands (if you didn't use the default).

H2: Potential Challenges and Solutions

• Port Conflicts: If both instances use the same ports, one will override the other. Ensure that applications running in different Docker instances use distinct ports.

• Resource Management: Two Docker instances consume more system resources (CPU, memory, disk space). Monitor resource usage to prevent performance issues. You might need to adjust cgroups to limit resource consumption for each instance.

• Security: Exposing Docker over TCP (as shown above) is generally insecure for production environments. Use a secure network or dedicated socket for production deployments. Consider utilizing Docker Swarm or Kubernetes for enhanced cluster management if required.

H1: Conclusion

Running multiple Docker instances on a single Ubuntu server provides flexibility and isolation for diverse projects. By employing separate user accounts and custom configuration, you can manage these instances effectively. However, remember to prioritize security and resource management to maintain system stability and prevent conflicts. Remember to always back up your data and configurations.