http://www.infoq.com/articles/docker-future
....Docker - the story so far
Docker is a toolset for Linux containers designed to ‘build, ship and run’ distributed applications. It was first released as an open source project by DotCloud in March 2013. The project quickly became popular, leading to DotCloud rebranded as Docker Inc (and ultimately selling off their original PaaS business). Docker 1.0 was released in June 2014, and the monthly release cadence that led up to the June release has been sustained since.
The 1.0 release marked the point where Docker Inc considered the platform sufficiently mature to be used in production (with the company and partners providing paid for support options). The monthly release of point updates shows that the project is still evolving quickly, adding new features, and addressing issues as they are found. The project has however successfully decoupled ‘ship’ from ‘run’, so images sourced from any version of Docker can be used with any other version (with both forward and backward compatibility), something that provides a stable foundation for Docker use despite rapid change.
The growth of Docker into one of the most popular open source projects could be perceived as hype, but there is a great deal of substance. Docker has attracted support from many brand names across the industry, including Amazon, Canonical, CenturyLink, Google, IBM, Microsoft, New Relic, Pivotal, Red Hat and VMware. This is making it almost ubiquitously available wherever Linux can be found. In addition to the big names many startups are growing up around Docker, or changing direction to be better aligned with Docker. Those partnerships (large and small) are helping to drive rapid evolution of the core project and its surrounding ecosystem.
A brief technical overview of Docker
Docker makes use of Linux kernel facilities such as cGroups, namespaces and SElinux to provide isolation between containers. At first Docker was a front end for the LXC container management subsystem, but release 0.9 introduced libcontainer, which is a native Go language library that provides the interface between user space and the kernel.
Containers sit on top of a union file system, such as AUFS, which allows for the sharing of components such as operating system images and installed libraries across multiple containers. The layering approach in the filesystem is also exploited by the Dockerfile DevOps tool, which is able to cache operations that have already completed successfully. This can greatly speed up test cycles by taking out the wait time usually taken to install operating systems and application dependencies. Shared libraries between containers can also reduce RAM footprint.
A container is started from an image, which may be locally created, cached locally, or downloaded from a registry. Docker Inc operates the Docker Hub public registry, which hosts official repositories for a variety of operating systems, middleware and databases. Organisations and individuals can host public repositories for images at Docker Hub, and there are also subscription services for hosting private repositories. Since an uploaded image could contain almost anything Docker Hub provides an automated build facility (that was previously called ‘trusted build’) where images are constructed from a Dockerfile that serves as a manifest for the contents of the image.
