2 dockers installed on ubuntu server

3 min read 13-02-2025

Meta Description: Learn how to install and manage two separate Docker instances on a single Ubuntu server, enhancing resource isolation and application management. This comprehensive guide covers installation, configuration, and best practices for advanced Docker deployments. (158 characters)

Introduction: Why Run Two Docker Instances?

Running multiple Docker instances on a single Ubuntu server offers several advantages. It allows for better resource isolation, separating applications and their dependencies for enhanced security and stability. This is crucial for managing different projects, teams, or environments (e.g., development vs. production). This guide will walk you through the process of setting up and managing two Docker installations on your Ubuntu server.

Method 1: Using Different Ports and Socket Files

This approach involves installing Docker twice, configuring each instance to use a unique port and socket file. This provides strong isolation but requires managing each instance individually.

Step 1: Install Docker (First Instance)

Follow the standard Docker installation instructions for Ubuntu. This typically involves updating your package list and installing the docker.io package:

sudo apt update
sudo apt install docker.io
sudo systemctl start docker
sudo systemctl enable docker

Step 2: Install Docker (Second Instance) - Altering Port and Socket

For the second instance, we need to modify the installation process. We'll change the Docker daemon's port and socket file location. Note: This requires careful planning to avoid port conflicts with other services.

First, create a new directory for the second Docker instance:

sudo mkdir /opt/docker2

Download the Docker installation package again (to ensure a clean install):

wget https://download.docker.com/linux/ubuntu/dists/$(lsb_release -cs)/amd64/packages/docker.io/docker-ce_*.deb

Now install it into the new directory, specifying the alternative socket and port:

sudo dpkg -i --force-architecture /opt/docker2/docker-ce_*.deb 
sudo systemctl daemon-reload #Important for newer docker installs

Create systemd service file to start docker on new port and socket:

sudo tee /etc/systemd/system/docker2.service << EOF
[Unit]
Description=Docker 2 Instance
After=network-online.target
Requires=network-online.target

[Service]
Type=notify
EnvironmentFile=/etc/default/docker #Use defaults as starting point
ExecStart=/usr/bin/dockerd -H unix:///opt/docker2/docker.sock -H tcp://0.0.0.0:2376 # specify the correct path to your socket and port 2376
ExecReload=/usr/bin/systemctl reload docker2
KillMode=process
Restart=always
RestartSec=10
TimeoutStartSec=0

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl start docker2
sudo systemctl enable docker2

Remember to replace 2376 with a port not used by another service and /opt/docker2/docker.sock with your chosen socket file path.

Step 3: Verify Installations

Check both Docker instances are running and accessible:

#First Instance
sudo docker version
#Second Instance
sudo docker -H tcp://localhost:2376 version

You should see output confirming both installations. Remember to use the -H flag with the correct socket/port for the second instance.

Method 2: Using Docker Compose and Separate Projects (Recommended)

This is generally a preferred method, especially for larger projects. It uses Docker Compose to manage each project in its own environment within a single Docker installation. This keeps things cleaner and simpler, particularly as your needs grow.

Step 1: Install Docker Compose

Install Docker Compose using pip:

sudo curl -L https://github.com/docker/compose/releases/download/v2.15.1/docker-compose-linux-x86_64 -o /usr/local/bin/docker-compose
sudo chmod +x /usr/local/bin/docker-compose

Step 2: Create Separate Projects

Organize your Docker projects into distinct directories. Each directory will have its own docker-compose.yml file describing the services for that project.

For example, project1 and project2 directories might contain the following docker-compose.yml files:

project1/docker-compose.yml:

version: "3.9"
services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"

project2/docker-compose.yml:

version: "3.9"
services:
  app:
    image: my-custom-app:latest
    ports:
      - "8081:80"

Step 3: Running Projects

Navigate to each project directory and run:

cd project1
docker-compose up -d
cd ../project2
docker-compose up -d

This approach leverages the power of Docker Compose without requiring multiple Docker daemon installations, simplifying management.

Conclusion

Managing multiple Docker instances allows for greater control and isolation within your Ubuntu server. While installing separate instances (Method 1) offers strong isolation, using Docker Compose (Method 2) provides a more streamlined and manageable approach for most users. Choose the method that best suits your needs and complexity. Remember to always secure your Docker instances with appropriate access controls and regular updates.