KVM vs libvirt: What are the differences?

Introduction

KVM and libvirt are both widely used in the field of virtualization, but they serve different purposes. KVM is a virtualization infrastructure for the Linux kernel, while libvirt is a toolkit that provides a common interface for managing various virtualization technologies, including KVM. In this article, we will explore the key differences between KVM and libvirt.

1. Native Kernel Integration: KVM stands for Kernel-based Virtual Machine and is a feature of the Linux kernel itself. It leverages the hardware virtualization extensions found in modern processors to create virtual machines. On the other hand, libvirt is a user-space toolkit that provides an abstraction layer between the virtualization technologies and the higher-level management tools. It uses KVM as one of the virtualization backends but can also work with other virtualization technologies like Xen, QEMU, and VirtualBox.

2. Virtual Machine Management Interface: While both KVM and libvirt can be used to manage virtual machines, they differ in their approach. KVM provides a low-level interface that is specific to the virtualization technology itself. It requires direct interaction with the KVM kernel module and uses command-line tools or specialized management applications. On the contrary, libvirt provides a high-level, uniform interface that abstracts the underlying virtualization technologies. It offers APIs and command-line tools that can work with multiple virtualization technologies, including KVM. This allows system administrators to manage virtual machines consistently across different hypervisors.

3. Rich Set of Features: KVM provides a rich set of virtualization features that are tightly integrated with the Linux kernel. It supports features like live migration, virtual CPU hot-plugging, memory ballooning, and NUMA support. These features enable advanced virtualization capabilities and performance optimizations. On the other hand, libvirt doesn't introduce any new features by itself. It serves as a management layer that abstracts the features provided by the underlying virtualization technologies. Therefore, the rich set of features available in KVM can be accessed and utilized through the libvirt interface.

4. Community Support and Ecosystem: KVM has a strong community and ecosystem backing due to its integration with the Linux kernel. It benefits from continuous development, bug fixes, and security enhancements by the open-source community. Additionally, KVM shares common tools and utilities with the Linux ecosystem, making it compatible with existing Linux administration tools. On the other hand, libvirt has its own community and ecosystem that supports the toolkit and its associated technologies. Libvirt offers a unified management experience for multiple virtualization technologies, making it easier for system administrators to adopt and manage different hypervisors.

5. Ease of Use and Abstraction Level: KVM, being a low-level virtualization technology, requires a deep understanding of the underlying concepts and interfaces. It is more suitable for advanced users who require fine-grained control over the virtualization environment. On the contrary, libvirt provides a higher level of abstraction by hiding the complexities of the underlying virtualization technologies. It offers a more user-friendly approach for managing virtual machines with simpler APIs and tools. This makes it accessible to a wider range of users, including beginners and less experienced system administrators.

6. Extensibility and Integration: KVM, being integrated with the Linux kernel, benefits from the extensibility and integration capabilities of the Linux ecosystem. It can leverage various Linux kernel components and modules to enhance its functionality. On the other hand, libvirt provides an extensible framework that can integrate with third-party management tools, like cloud management platforms and virtualization management consoles. This allows system administrators to integrate libvirt with their existing infrastructure and management workflows.

In summary, KVM is a virtualization infrastructure integrated with the Linux kernel, while libvirt is a toolkit that provides a common interface for managing various virtualization technologies, including KVM. The key differences between KVM and libvirt include their approach to virtualization, virtual machine management interface, set of features, community support, ease of use, and extensibility.