Docker vs LXC vs rkt: What are the differences?

Key Differences between Docker, LXC, and rkt

Introduction

In the world of containerization, Docker, LXC (Linux Containers), and rkt (pronounced "rocket") are three popular tools that help developers create and manage lightweight, isolated environments. Although they serve similar purposes, there are significant differences between them in terms of architecture, features, and community support. This article aims to highlight the key distinctions among Docker, LXC, and rkt.

1. Containerization Engine: Docker is a containerization platform that uses a client-server architecture, with the Docker daemon acting as the server and the Docker CLI serving as the client. On the other hand, LXC is a userspace interface for the Linux kernel containment features and operates directly on the Linux kernel. rkt, developed by CoreOS, follows an application container model and focuses on security and simplicity, using pod-based architecture for managing containers.

2. Image Format: Docker uses a layered image format based on the Docker Image Specification. It builds images using Dockerfiles and stores them in a Docker registry. LXC, being more barebones, does not have a dedicated image format but relies on operating system templates or snapshots. rkt, similar to Docker, supports images but uses an industry-standard App Container Image (ACI) format, which is compatible with other container runtimes.

3. Orchestration and Compatibility: Docker has extensive support for orchestration through Docker Swarm, enabling clustering, scaling, and load balancing of containers across multiple nodes. It also has strong integration with other containerization tools such as Kubernetes. LXC, being a fundamental component of LXD (Linux Container Hypervisor), provides more advanced cluster management and device pass-through capabilities. rkt, by design, does not include native orchestration features but instead aims to be compatible with existing orchestration solutions like Kubernetes and Mesos.

4. Security and Isolation: Docker primarily relies on namespaces and control groups provided by the Linux kernel to ensure container isolation. It introduces an additional layer of security through the use of Docker Engine, which manages container execution. LXC, being more low-level, provides stronger isolation as it leverages kernel cgroups and namespaces directly. rkt, with its focus on security, utilizes a simpler and reduced trusted computing base, reducing potential attack vectors. It also supports features like seccomp and native sandboxing, enhancing container security.

5. Community and Ecosystem: Docker has gained significant community traction and has an extensive ecosystem with a vast collection of pre-built images and tools contributed by the community. It enjoys wide adoption and has become a standard in the containerization landscape. While LXC has a smaller but dedicated community, it benefits from being a part of the larger Linux ecosystem. rkt, although not as mature as Docker, has an active community and complements the CoreOS ecosystem, providing features like automatic updates and easy deployments.

6. Runtime Performance and Resource Efficiency: Docker, with its layered image approach and shared container OS, provides lightweight and efficient runtime performance. It employs copy-on-write techniques to optimize resource utilization. LXC, being more lightweight than Docker, has lower overhead and better performance for host-level operations. rkt, designed with simplicity and minimalism in mind, offers comparable performance to Docker but with less resource overhead due to its modular design.

In summary, Docker is a highly popular container platform with a strong emphasis on container management and orchestration. LXC, being a Linux kernel-level solution, provides better isolation and control but with a lower-level interface. rkt focuses on simplicity, security, and compatibility with other container platforms, making it a suitable choice for specific use cases.