Docker versus Podman: A Comparison

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This article expects readers to have some knowledge of containerization and virtualization in general. If you are new to the topic, consider reading introductory materials. You can also check out my detailed writings on Docker and Podman.

Docker and Podman are two popular containerization tools that have gained significant traction in the software development and deployment landscape. Both tools provide the ability to create, manage, and deploy containers, but they have different architectures and philosophies. In this article, we will compare them, highlighting their key differences, advantages, and disadvantages.

What is Containerization?

Containerization is a lightweight form of virtualization¹ that allows developers to package applications and their dependencies into isolated environments called containers. This approach ensures that applications run consistently across different environments, such as development, testing, and production, as well as across different operating systems. Containers share the host operating system's kernel, making them more efficient than traditional virtual machines².

Docker

Docker is a platform that provides a set of tools for building, running, and managing containers. It was first released in 2013 and has since become the de facto standard for containerization. Docker offers a user-friendly command-line interface (CLI) and a graphical user interface (GUI) called Docker Desktop, which make it easy to manage containers and images.

Architecture

Docker uses a client-server architecture, where the Docker client communicates with the Docker daemon to manage containers. The Docker daemon runs as a background service and is responsible for managing containers, images, networks, and volumes. The Docker client sends commands to the daemon, which then executes them. This architecture allows for easy management of containers, but it also means that the Docker daemon must be running for any container operations to succeed.

• Docker Client (CLI or REST API): The interface used to communicate with the Docker daemon.
• Docker Daemon (dockerd): The main service that manages containers, images, and more.
• Containerd: The container runtime Docker uses under the hood.
• Docker Objects: Includes images, containers, volumes, and networks.
• Docker Registry: Stores Docker images (e.g., Docker Hub or private registries).

Advantages of Docker

• Mature Ecosystem: Docker has a large and mature ecosystem with extensive documentation, community support, and third-party tools.
• User-Friendly: Docker provides a user-friendly CLI and GUI, making it easy for developers to get started with containerization.
• Wide Adoption: Docker is widely adopted in the industry, making it easier to find resources, tutorials, and community support.

Disadvantages of Docker

• Daemon Dependency: Docker requires the Docker daemon to be running, which can be a single point of failure and may introduce security concerns.
• Root Privileges: Docker typically requires root privileges to run, which can pose security risks, especially in multi-tenant environments.
• Complexity: Docker's architecture can be complex, especially for beginners. The interaction between the Docker client, daemon, and containerd can be confusing.

Podman

Podman is a container management tool developed by Red Hat and released in 2018. It is designed to be a drop-in replacement for Docker, providing a similar command-line interface and functionality. However, Podman has a key difference: it does not require a daemon to run. Instead, Podman uses a daemon-less architecture, meaning each Podman command runs as a separate process. This approach provides better security and allows users to run containers without requiring root privileges.

Architecture

Podman's architecture is simpler than Docker's, as it does not rely on a central daemon. Each Podman command runs as a separate process, allowing users to run containers without a long-running service. Podman uses the containerd runtime for managing containers, similar to Docker, but it does not require a daemon to manage them.

• Daemon-less: Podman does not require a background service like Docker.
• Rootless Support: Containers can be run securely by non-root users.
• Libpod Library: The core library that manages pods, containers, and images.
• runc/crun: OCI-compliant container runtimes used to run containers.
• CNI: Container Network Interface plugins for networking.
• containers/image & containers/common: Libraries for image handling and shared utilities.

Advantages of Podman

• Daemon-less Architecture: Podman does not require a long-running daemon, reducing complexity and potential security risks.
• Rootless Containers: Podman allows users to run containers without root privileges, enhancing security in multi-tenant environments.
• Compatibility with Docker: Podman provides a Docker-compatible CLI, making it easy for Docker users to transition to Podman without significant changes to their workflows.

Disadvantages of Podman

• Less Mature Ecosystem: Podman is newer than Docker, so its ecosystem is less mature, with fewer third-party tools and resources available.
• Compatibility Issues: While Podman aims to be Docker-compatible, there may be some differences in behavior or features that can cause compatibility issues with existing Docker workflows.

Comparison

Feature	Docker	Podman
What it is	Container engine	Container engine (daemon-less)
Developed by	Docker Inc.	Red Hat
Released in	2013	2018
Daemon	Yes (monolithic dockerd daemon)	No (daemon-less)
Rootless mode	Available, but less mature	Native and first-class support
Container runtime	Uses containerd under the hood	Uses runc or can integrate with CRI-O
Client-server model	Yes (Docker client talks to Docker daemon)	No (Podman runs commands directly)
Systemd integration	Indirect or through wrappers	Native systemd unit generation (podman generate systemd)
CLI compatibility	Native	Docker CLI-compatible (alias docker=podman)
Swarm mode	Yes	No
Kubernetes support	Not native, but with 3rd party	Native (podman generate kube)
Image build	docker build	podman build or Buildah (under the hood)
Docker Compose	Supported with docker-compose	Podman Compose (podman-compose, community-supported)
Rootless containers	Available	Default / preferred mode
User namespaces	Optional	Used extensively
SELinux support	Limited	Native SELinux integration

Conclusion

When choosing between Docker and Podman, there is no one-size-fits-all solution. Consider your specific use case and requirements. Both tools have their strengths and weaknesses, and the best choice depends on your needs. Here are some scenarios where each tool might be more suitable:

Choose Docker if:

• You need a mature ecosystem with extensive community support.
• You prefer a user-friendly CLI and GUI for managing containers.
• You are already using Docker in your development workflow and want to maintain compatibility.

Choose Podman if:

• You prioritize security and want to run containers without root privileges.
• You prefer a simpler, daemon-less architecture.
• You want to leverage systemd integration for managing containers as system services.

Further Exploration

• Docker Documentation: Official documentation for Docker.
• Podman Documentation: Official documentation for Podman.
• The differences between Docker, containerd, CRI-O and runc: A detailed explanation of the differences between Docker, containerd, CRI-O, and runc.
• The Moby Project: Moby is an open-source project that provides the components for building container-based systems, including the Docker Engine.

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Footnotes

1. Virtualization is a technology that allows multiple operating systems to run on a single physical machine, providing isolation and resource management. ↩

2. Virtual machines (VMs) are software emulations of physical computers that run an entire operating system, including its kernel. They provide strong isolation and can run different OSes on the same hardware, but they are more resource intensive compared to containers. ↩