Why did Docker containers become so popular? To understand the answer, you have to identify Docker’s killer features — the ones that set Docker apart from other container frameworks, as well as virtual machines.
It can seem very surprising that Docker has become as popular as it is. Docker was not the first containerization platform; frameworks including LXC predated Docker by years. And when Docker originated, its functionality was in many respects not very different from traditional virtualization.
Docker’s Killer Features
Yet there’s no disputing that, today, Docker stands out from virtual machine platforms including VMware and KVM, as well as alternative container frameworks.
Why? Because Docker offers several features not available elsewhere. They include:
- Faster startup time. Containers can start in seconds, whereas virtual machines take minutes. This is one of the features that made Docker stand out from VMware, KVM and the like. LXC containers also have fast start times, but LXC lacks many of Docker’s other important features.
- Small attack surface. A containerized application that runs using Docker includes a minimal amount of overhead. From a security perspective, this is attractive because it means Dockerized applications have a smaller attack surface.
- Open-source licensing. From the start, most of the Docker stack has been open-source. Specifically, Docker software was licensed mostly under Apache and MIT-style licenses. These licenses, which are more liberal than the GPL (which governs Linux, among other older open-source platforms) give developers a great deal of flexibility. They make Docker different not only from closed-source platforms such as VMware, but also from KVM and LXC, both of which are governed primarily by the GPL or closely related licenses.
- Cross-platform support. While Docker initially was a Linux-only technology, that is no longer the case. You can now run Docker containers in almost any type of environment or operating system. This is a tremendously distinctive feature. While alternative deployment frameworks, including VMware, are cross-platform, technologies such as KVM and LXC remain tied to particular operating systems.
- A burgeoning ecosystem. The years following Docker’s public release in 2013 saw a thriving ecosystem grow up around Docker. Established companies (including Red Hat and Microsoft) as well as startups (from CoreOS to Twistlock to Rancher) contributed code, documentation, standards, marketing efforts and much more to help build a diverse and dynamic ecosystem surrounding Docker. VMware, KVM, LXC and the like have not come close to Docker in this respect.
If you want to understand why Docker has become so wildly popular in a few short years, these five features are at the center of the answer.