In this article, we'll explore the strengths and limitations of KVM, OpenVZ, and LXC, and compare the difference between containers and hypervisors.
By the end of it, you'll know for certain which virtualization technology is right for you and your use case.
Let's dive in.
Containers vs. hypervisors
Before diving into the specifics of KVM, OpenVZ, and LXC, it's essential to grasp the fundamental difference between containers and hypervisors.
Containers, such as those provided by OpenVZ and LXC, leverage a shared host operating system and isolate applications and their dependencies within lightweight, self-contained environments.
This approach enables high density and efficient resource utilization, as multiple containers can run on a single host without the overhead of a full operating system.
On the other hand, hypervisors, like KVM, create virtual machines (VMs) that emulate a complete hardware environment.
Each VM runs its own operating system and has dedicated resources, providing strong isolation and the ability to run diverse workloads.
Hypervisors offer greater flexibility and security at the cost of higher resource consumption compared to containers.
KVM
KVM has emerged as a prominent hypervisor solution, leveraging the Linux kernel to create virtual machines.
With KVM, each VM runs its own separate kernel, ensuring strong isolation and enhanced security. This makes KVM an attractive choice for environments that prioritize data protection and compliance.
One of KVM's key strengths lies in its ability to deliver high performance while supporting a wide range of operating systems, including Linux, Windows, and more. This versatility positions KVM as a compelling option for organizations with diverse workloads and multi-OS requirements.
However, the full virtualization approach of KVM comes with a higher resource overhead compared to container-based solutions. VMs managed by KVM consume more resources, which can impact overall efficiency and scalability.
Additionally, managing KVM environments and networking can be more complex, requiring specialized skills and tools.
Other hypervisor options (Xen & VMware ESXi)
While KVM has gained significant popularity as a hypervisor solution, it's important to recognize that there are other notable hypervisor options available in the market.
Two standout examples are Xen and VMware ESXi.
Xen is an open-source hypervisor that provides strong isolation and supports a wide range of operating systems, making it a viable choice for organizations seeking flexibility and security.
VMware ESXi, on the other hand, is a proprietary hypervisor known for its robustness, performance, and extensive ecosystem of tools and support. VMware ESXi offers advanced features such as live migration, high availability, and centralized management, making it a preferred choice for enterprises with mission-critical workloads.
Both Xen and VMware ESXi have established themselves as reliable and feature-rich hypervisor solutions, but KVM has surpassed them as of 2024.
OpenVZ
OpenVZ is a container-based virtualization solution that excels in high-density deployments.
By enabling a single physical server to host numerous isolated containers, OpenVZ maximizes resource utilization and allows for efficient scaling.
One of OpenVZ's standout features is its ability to rapidly provision and manage containers. The flexibility and speed of container creation, modification, and deletion make OpenVZ well-suited for scenarios that demand quick scalability and agile resource allocation.
However, OpenVZ's reliance on a shared host kernel raises concerns regarding security and stability. Vulnerabilities in the kernel can potentially impact all containers running on the server.
Also, OpenVZ is only designed to run Linux. It can't run Windows.
LXC
LXC, another container-based solution, offers lightweight virtualization capabilities with a focus on simplicity and performance.
By leveraging Linux kernel features such as namespaces and cgroups, LXC provides process and resource isolation while maintaining near-native performance.
LXC's flexibility in supporting a wide range of Linux distributions makes it an attractive choice for organizations seeking to run diverse Linux workloads on a single host.
The minimal overhead of LXC containers enables efficient resource utilization and scalability.
To further enhance LXC's capabilities, LXD, now owned by Canonical (the publisher of Ubuntu), enters the picture.
While not a virtualization technology itself, LXD builds upon LXC, offering advanced management features, improved security, and a user-friendly interface.
With LXD, you can leverage container snapshots, live migration, and remote management, making it an appealing choice for those who prefer the lightweight nature of LXC but require more sophisticated management capabilities.
Final comparison
| Feature | KVM | LXC | LXD | OpenVZ | Xen | ESXi |
|---|---|---|---|---|---|---|
| Type | Full Virtualization (Integrated into Linux kernel) | Containerization | Container Management (over LXC) | Containerization | Full Virtualization (Paravirtualization & HVM) | Full Virtualization (Type-1 Hypervisor) |
| OS Support | Wide (Linux, Windows, etc.) | Linux-based only | Linux-based only | Linux-based only | Wide (Linux, Windows, etc., with optimizations for paravirtualized guests) | Wide (Linux, Windows, etc.) |
| Isolation Level | High (separate kernel) | Medium (shared kernel) | Medium (shared kernel) | Medium (shared kernel) | High (separate kernel, enhanced in paravirtualization) | High (separate kernel) |
| Performance Overhead | Moderate (Can be optimized with hardware acceleration) | Low | Low | Low | Low to Moderate (Lower with paravirtualization) | Low (Optimized for efficiency) |
| Use Case | General-purpose virtualization, scenarios requiring strong isolation | Development, lightweight production apps | Enhanced management and security for LXC containers | High-density virtualization, rapid scalability | General-purpose virtualization, optimized for performance in paravirtualized environments | Enterprise virtualization solutions, optimized for datacenter and cloud environments |
| Primary Advantage | Strong isolation, broad OS support, integrated into Linux for ease of use | Efficient resource use, minimal overhead, simple setup | Simplifies LXC management, advanced features, improved security | High container density, rapid provisioning, efficient Linux virtualization | Efficient resource utilization, especially with paravirtualization, versatile virtualization modes | Highly efficient, enterprise-grade features, robust resource management |
| Security | Enhanced by VM isolation, dependent on Linux kernel security | Dependent on host kernel security | Enhanced security models over LXC | Dependent on host kernel security | Enhanced by VM isolation, paravirtualization reduces attack surface | Enhanced by VM isolation, proprietary optimizations for security |
Xen and VMware EXSi while solid options for some have in many ways been surpassed by KVM.
KVM's strong isolation, multi-OS support, and robust security make it a compelling choice for many. However, the higher resource overhead and complexity of managing KVM environments should be considered.
OpenVZ excels in high-density container deployments, offering rapid provisioning and efficient resource utilization. Its ability to scale quickly makes it well-suited for environments that require agility and elasticity. However, the shared kernel model and focus on Linux workloads may limit its applicability in certain scenarios.
LXC, paired with LXD, provides a lightweight and flexible containerization solution with enhanced management capabilities. The near-native performance and simplicity of LXC make it an attractive choice for organizations seeking to optimize resource utilization and streamline their Linux workloads.
Conclusion
Ultimately, the decision between KVM, OpenVZ, and LXC in 2024 will depend on factors such as performance requirements, security needs, workload diversity, and management preferences.
Personally over here at xTom, our favorite virtualization technology is KVM, as it gives you as close to a bare bones experience as possible. From performance to isolation.
You could even run OpenVZ or LXC within your KVM VPS. Best of all worlds.
Thanks for reading!