Docker vs containerd vs rkt: What are the differences?

Introduction

Docker, containerd, and rkt are all container runtimes that allow you to package and deploy applications within an isolated environment. While they serve a similar purpose, there are key differences between them that set them apart.

1. Portability: Docker is known for its strong portability, allowing containers to run consistently across different platforms. containerd focuses on providing a robust container runtime with a simplified API, while rkt prioritizes on leveraging existing Linux tools and standards for improved compatibility and security.

2. Architecture: Docker uses a client-server architecture where the Docker daemon manages containers and images. containerd is designed as a lower-level container runtime specifically for Docker, providing a simpler interface for container management. On the other hand, rkt follows a different decentralized approach, leveraging a pod-based architecture for managing containers with pod manifests.

3. Security: Docker provides a comprehensive set of security features, such as image signing and verification, user namespaces, and container isolation. containerd inherits most of its security features from Docker and focuses on simplifying the container runtime interface. rkt, on the other hand, emphasizes on security by leveraging UNIX principles and integrating SELinux and AppArmor for enhanced isolation.

4. Community and Adoption: Docker has a large and active community, making it the most widely used container runtime. containerd benefits from being part of the Docker ecosystem, leveraging its popularity and community support. rkt, although being an alternative to Docker, has a smaller community and adoption compared to Docker and containerd.

5. Orchestration Support: Docker provides several built-in orchestration tools, like Docker Swarm and Kubernetes. containerd, being part of the Docker ecosystem, can be used with the same orchestration tools. rkt, on the other hand, can be integrated with various orchestration frameworks, including Kubernetes and Mesos, providing flexibility in choosing an orchestration platform.

6. Runtime Overhead: Docker implementations often have more overhead due to the additional features and flexibility provided. containerd, being a lower-level runtime, reduces this overhead by focusing on core container management features. rkt aims to provide a minimalistic runtime with a smaller footprint, achieving lower runtime overhead compared to Docker.

In summary, Docker is known for its strong portability and extensive community, while containerd simplifies the container runtime interface and leverages the Docker ecosystem. rkt emphasizes security, compatibility, and minimalism, making it a viable alternative to Docker and containerd.