Unikernel vs. Containers: What's the Difference?

December 1, 2022


Application deployment is a process that requires development teams to achieve a balance between conserving resources and ensuring the app runs smoothly. While virtualization is a logical choice in the world of multi-platform apps and microservices, virtual machines are rarely considered a viable solution due to the significant resource overhead they create.

The rise of alternative virtualization solutions is tied to the efforts to create a resource-friendly application deployment option.

This article will compare unikernels and containers, two technologies aiming to reduce the virtualization footprint while supporting optimal app performance.

Unikernels vs. Containers: What's the difference?

What Is a Container?

A container is a virtualization unit that contains an application packaged alongside its dependencies. The dependencies include external libraries, system tools, and other packages necessary for the application to work correctly.

Containers run on top of a container engine, such as Docker, containerd, or CRI-O, which connects them with the additional operating system components. Therefore, a single host OS kernel powers many containers simultaneously.

The diagram below illustrates the relationship between the containers and the OS kernel running on a hypervisor.

Container architecture diagram.

What Is a Unikernel?

A unikernel is a machine image that contains everything necessary for application execution, including the operating system component. This property makes unikernels completely self-sufficient and able to run independently on top of a bare metal hypervisor.

Unikernel architecture diagram.

The tools for packaging applications into unikernels, such as UniK, MirageOS, and Clive, combine the app's source code with dependencies, device drivers, and OS libraries. The final product is a lightweight operating system capable of performing a single function - running the packaged application.

Unikernel vs. Containers: Deployments

Deploying an application requires careful resource planning. A successful app deployment:

  • Responds well to infrastructure scaling.
  • Minimizes the differences between various deployment platforms.
  • Facilitates code management, monitoring, and data collection.
  • Ensures that the code is secure.

The following sections introduce you to basic facts about container and unikernel deployments.

Deployment via Containers

A container-based deployment starts with an app image that contains the application source code and the dependencies. The container engine uses the image to create containers, i.e., virtualized runtime environments that run the packaged application.

As mentioned before, containers utilize the kernel of the underlying operating system. This OS is almost exclusively Linux since the Linux kernel supports resource assignment to specific processes through its Namespaces feature.

Deployment via Unikernels

Unikernels achieve a higher level of independence than containers since they pack the OS component inside each deployment unit. However, the packaged system is not a full-fledged OS like Linux or Windows. Instead, it is a small kernel known as a library operating system, which supports a single user and a single address space.

Although the components inside unikernels handle all app-related system calls, unikernels are still not completely independent. Since they cannot allocate resources independently, they need a hypervisor to connect them with the hardware infrastructure.

Unikernel vs. Containers: Key Differences

The following table sums up the essential differences between unikernels and containers mentioned in the article:

Share the kernel of the host OS.Include a small kernel in each deployment unit.
Offer native performance on Linux.Performance is not limited by the host OS.
Simple to create from an image.Require advanced skills to create.
Designed to run multiple processes.Designed to run a single process.
Linux handles resource allocation.The hypervisor handles resource allocation.

Unikernel vs. Containers: How to Choose?

Choose unikernels if you want to:

  • Minimize resource consumption. Unikernels eliminate layers of abstraction and create a lightweight, resource-friendly deployment platform.
  • Maximize security. With their simple design, unikernels help increase security by reducing the attack surface.
  • Achieve complete platform independency. While containers can also be called independent, they rely on the Linux kernel. It means that their performance suffers on other OSs, such as Windows and macOS, where an additional level of virtualization is necessary.

Choose containers if you want to:

  • Run an app that features complex workloads. While unikernel performance surpasses containers in single-thread processing, multi-thread workloads are still processed faster using containers.
  • Want a well-documented, supported solution. Docker and Kubernetes brought containers into the mainstream, so it is easy to find answers to most container-related issues.
  • Prefer simple deployments. Unikernels are challenging to assemble and require extensive knowledge of both the packaged application and the virtualization technology. On the other hand, using container platforms such as Docker requires almost no additional technical knowledge.

Note: Complex workloads benefit from computing instances that are fine-tuned to the specific processing, memory, and storage needs of the project. Our Bare Metal Cloud offers instances that are easy to deploy and feature no hypervisor overhead.


The article introduced you to containers and unikernels, two software virtualization technologies. It compared the container and unikernel architectures and offered advice on choosing the technology that suits your needs.

If you decide to work with containers, you should also learn about the benefits of container orchestration.

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Marko Aleksic
Marko Aleksić is a Technical Writer at phoenixNAP. His innate curiosity regarding all things IT, combined with over a decade long background in writing, teaching and working in IT-related fields, led him to technical writing, where he has an opportunity to employ his skills and make technology less daunting to everyone.
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