LXC vs rkt: What are the differences?

Introduction

In this article, we will discuss the key differences between LXC and rkt container runtimes.

1. Container Technology LXC (Linux Containers) is an operating system-level virtualization method that allows running multiple isolated Linux systems (containers) on a single host. It uses Linux kernel features like namespaces, cgroups, and chroot to provide resource and process isolation. On the other hand, rkt is a container runtime developed by CoreOS that focuses on security, simplicity, and composability. It follows the container-runtime specification and can run Docker images as well.

2. Image Format LXC uses a traditional image format called LXCFS (Linux Container Filesystem). This format contains a tarball with a full root filesystem. In contrast, rkt uses the App Container Image (ACI) format, which consists of a compressed tarball that contains both the application and its dependencies. The ACI format is lightweight, easier to distribute, and provides better security by separating the application from the underlying OS.

3. Networking Model LXC uses the traditional networking model, where containers share the network namespace with the host. This means that containers can have their own IP addresses and maintain direct network connections. In contrast, rkt follows a more secure and isolated networking model. It uses a virtual ethernet pair (veth) to connect the container to the host, allowing communication through the bridge interface.

4. Container Orchestration Support LXC provides limited container orchestration capabilities through the LXD daemon, which manages the containers and provides an API for remote management. However, it does not have native support for container orchestration frameworks like Kubernetes. On the other hand, rkt was designed with a modular and composable architecture, making it more suitable for integrating with container orchestration frameworks. It has native support for Kubernetes and can be used as a runtime in a Kubernetes cluster.

5. Security Focus While both LXC and rkt prioritize security, rkt has a more security-centric approach. Rkt aims to provide isolation without relying on the host OS, making it more resistant to attacks. It also implements a CVE (Common Vulnerabilities and Exposures) feature that allows users to verify the security of the images they are running. LXC, although secure, does not offer the same level of isolation and security features as rkt.

6. Runtime Performance LXC is known for its efficient and lightweight performance. The use of Linux kernel features enables fast container creation and minimal resource usage. However, rkt is also designed for performance, focusing on simplicity and speed. It employs features like podman and KVM to provide efficient container runtime performance.

In summary, LXC is a Linux OS-level virtualization method, while rkt is a container runtime emphasizing security, simplicity, and composability. LXC uses the LXCFS image format and traditional networking model, while rkt uses the ACI format and a more isolated networking model. Rkt has better container orchestration support, a stronger security focus, and comparable runtime performance to LXC.