How to Use Docker Compose with Podman on AlmaLinux

As containerization becomes integral to modern development workflows, tools like Docker Compose and Podman are gaining popularity for managing containerized applications. While Docker Compose is traditionally associated with Docker, it can also work with Podman, a daemonless container engine. AlmaLinux, a stable, community-driven operating system, offers an excellent environment for combining these technologies. This guide will walk you through the process of using Docker Compose with Podman on AlmaLinux.

Why Use Docker Compose with Podman on AlmaLinux?

What is Docker Compose?

Docker Compose is a tool for defining and managing multi-container applications using a simple YAML configuration file. It simplifies the orchestration of complex setups by allowing you to start, stop, and manage containers with a single command.

What is Podman?

Podman is a lightweight, daemonless container engine that is compatible with Docker images and commands. Unlike Docker, Podman does not require a background service, making it more secure and resource-efficient.

Why AlmaLinux?

AlmaLinux provides enterprise-grade stability and compatibility with Red Hat Enterprise Linux (RHEL), making it a robust choice for containerized workloads.

Combining Docker Compose with Podman on AlmaLinux allows you to benefit from the simplicity of Compose and the flexibility of Podman.

Prerequisites

Before we begin, ensure you have:

1. AlmaLinux installed and updated.
2. Basic knowledge of the Linux command line.
3. Podman installed and configured.
4. Podman-Docker and Docker Compose installed.

Step 1: Install Podman and Required Tools

Install Podman

First, update your system and install Podman:

sudo dnf update -y
sudo dnf install podman -y

Verify the installation:

podman --version

Install Podman-Docker

The Podman-Docker package enables Podman to work with Docker commands, making it easier to use Docker Compose. Install it using:

sudo dnf install podman-docker -y

This package sets up Docker CLI compatibility with Podman.

Step 2: Install Docker Compose

Docker Compose is a standalone tool that needs to be downloaded separately.

1. Download Docker Compose
   Determine the latest version of Docker Compose from the GitHub releases page. Replace vX.Y.Z in the command below with the latest version:

   sudo curl -L "https://github.com/docker/compose/releases/download/vX.Y.Z/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
   

2. Make Docker Compose Executable

   sudo chmod +x /usr/local/bin/docker-compose
   

3. Verify the Installation

   docker-compose --version
   

Step 3: Configure Podman for Docker Compose

To ensure Docker Compose works with Podman, some configurations are needed.

Create a Podman Socket

Docker Compose relies on a Docker socket, typically found at /var/run/docker.sock. Podman can create a compatible socket using the podman.sock service.

1. Enable Podman Socket:

   systemctl --user enable --now podman.socket
   

2. Verify the Socket:

   systemctl --user status podman.socket
   

3. Expose the Socket:
   Export the DOCKER_HOST environment variable so Docker Compose uses the Podman socket:

   export DOCKER_HOST=unix:///run/user/$UID/podman/podman.sock
   

   Add this line to your shell configuration file (~/.bashrc or ~/.zshrc) to make it persistent.

Step 4: Create a Docker Compose File

Docker Compose uses a YAML file to define containerized applications. Here’s an example docker-compose.yml file for a basic multi-container setup:

version: '3.9'

services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
    volumes:
      - ./html:/usr/share/nginx/html
    networks:
      - app-network

  app:
    image: python:3.9-slim
    volumes:
      - ./app:/app
    networks:
      - app-network
    command: python /app/app.py

networks:
  app-network:
    driver: bridge

In this example:

• web runs an Nginx container and maps port 8080 to 80.
• app runs a Python application container.
• networks defines a shared network for inter-container communication.

Save the file as docker-compose.yml in your project directory.

Step 5: Run Docker Compose with Podman

Navigate to the directory containing the docker-compose.yml file and run:

docker-compose up

This command builds and starts all defined services. You should see output confirming that the containers are running.

Check Running Containers

You can use Podman or Docker commands to verify the running containers:

podman ps

or

docker ps

Stop the Containers

To stop the containers, use:

docker-compose down

Step 6: Advanced Configuration

Using Environment Variables

Environment variables can be used to configure sensitive or environment-specific details in the docker-compose.yml file. Create a .env file in the project directory:

APP_PORT=8080

Modify docker-compose.yml to use the variable:

ports:
  - "${APP_PORT}:80"

Building Custom Images

You can use Compose to build images from a Dockerfile:

services:
  custom-service:
    build:
      context: .
      dockerfile: Dockerfile

Run docker-compose up to build and start the service.

Step 7: Troubleshooting Common Issues

Error: “Cannot connect to the Docker daemon”

This error indicates the Podman socket isn’t properly configured. Verify the DOCKER_HOST variable and restart the Podman socket service:

systemctl --user restart podman.socket

Slow Startup or Networking Issues

Ensure the app-network is properly configured and containers are connected to the network. You can inspect the network using:

podman network inspect app-network

Best Practices for Using Docker Compose with Podman

1. Use Persistent Storage:
   Mount volumes to persist data beyond the container lifecycle.

2. Keep Compose Files Organized:
   Break down complex setups into multiple Compose files for better manageability.

3. Monitor Containers:
   Use Podman’s built-in tools to inspect logs and monitor container performance.

4. Regular Updates:
   Keep Podman, Podman-Docker, and Docker Compose updated for new features and security patches.

5. Security Considerations:
   Use non-root users and namespaces to enhance security.

Conclusion

Docker Compose and Podman together offer a powerful way to manage multi-container applications on AlmaLinux. With Podman’s daemonless architecture and Docker Compose’s simplicity, you can create robust, scalable, and secure containerized environments. AlmaLinux provides a solid foundation for running these tools, making it an excellent choice for modern container workflows.

Whether you’re deploying a simple web server or orchestrating a complex microservices architecture, this guide equips you with the knowledge to get started efficiently. Experiment with different configurations and unlock the full potential of containerization on AlmaLinux!