Containerization is a lightweight alternative to full machine virtualization that involves encapsulating an application in a container with its own operating environment. This provides many of the benefits of loading an application onto a virtual machine, as the application can be run on any suitable physical machine without any worries about dependencies.
Containerization has gained recent prominence with the open-source Docker. Docker containers are designed to run on everything from physical computers to virtual machines, bare-metal servers, OpenStack cloud clusters, public instances and more.
Containerization vs. Virtualization via Traditional Hypervisors
The foundation for containerization lies in the LinuX Containers (LXC) format, which is a userspace interface for the Linux kernel containment features. As a result, containerization only works in Linux environments and can only run Linux applications.
This is in contrast with traditional hypervisors like VMware’s ESXi, Xen or KVM, wherein applications can run on Windows or any other operating system that supports the hypervisor.
Another key difference with containerization as opposed to traditional hypervisors is that containers share the Linux kernel used by the operating system running the host machine, which means any other containers running on the host machine will also be using the same Linux kernel.
Docker Not the Only Containerization Option
Docker may have been the first to bring attention to containerization, but it’s no longer the only container system option. CoreOS recently released a streamlined alternative to Docker called Rocket.
And Canonical, developers of the Ubuntu Linux-based operating system, has announced the LXD containerization engine for Ubuntu, which will also be integrated with OpenStack.
Microsoft is working on its own containerization technology called Drawbridge, which will likely be featured in Windows Server and Azure in the future. And Spoon is another Windows alternative that will enabled containerized applications to be run on any Windows machine that has Spoon installed, regardless of the underlying infrastructure.