Docker vs libvirt: What are the differences?

Introduction

This article highlights the key differences between Docker and libvirt. Docker and libvirt are both technologies used to manage virtualized environments, but they have distinct features and purposes.

1. Architecture: Docker is based on containerization technology, where applications run in isolated containers. It uses a base image and layers to create containers. On the other hand, libvirt is a virtualization abstraction library that supports various virtualization technologies such as KVM, QEMU, and Xen. It provides a common interface to manage virtual machines (VMs) and can be used with different hypervisors.

2. Isolation: Docker provides process-level isolation, where each container has its own isolated runtime environment. It ensures that containers are well isolated from each other and from the host system. In contrast, libvirt offers system-level isolation through full virtualization. It creates a complete virtual machine with its own kernel, ensuring stronger isolation between VMs and the host system.

3. Image Management: Docker focuses heavily on image management. It provides a Docker registry for storing and distributing container images. Docker images are lightweight and can be easily shared and deployed on different systems. On the other hand, libvirt does not have its own image management system. It relies on disk image formats like qcow2 or raw disk images to create and manage VMs.

4. Orchestration: Docker has built-in orchestration features, such as Docker Swarm and Kubernetes, which allow for scaling, load balancing, and automatic container management across multiple hosts. Docker Swarm enables the creation of swarm clusters for distributed container deployments. In comparison, libvirt primarily focuses on managing individual VMs and does not provide built-in orchestration capabilities.

5. Networking: Docker provides its own container network model (CNM) for networking between containers. It allows containers to communicate with each other using virtual networks, bridges, and port mappings. Docker also supports third-party networking plugins for advanced networking configurations. Libvirt, on the other hand, relies on the underlying virtualization technology (such as KVM or QEMU) for networking, which includes options like bridge networks and virtual switches.

6. Resource Management: Docker provides resource isolation and control through its resource management features. It allows users to allocate CPU, memory, and other resources to containers using policies and limits. Docker's resource management is more fine-grained and flexible. In contrast, libvirt provides basic resource management capabilities like CPU and memory allocation at the VM level. It does not offer the same level of granularity and control as Docker.

In summary, Docker and libvirt are both used for virtualization, but they have different architectural approaches, isolation mechanisms, image management systems, orchestration capabilities, networking models, and resource management features. Choosing between the two depends on the specific requirements of the virtualized environment.