Docker is an open platform for developers and sysadmins to build, ship, and run distributed applications. Consisting of Docker Engine, a portable, lightweight runtime and packaging tool, and Docker Hub, a cloud service for sharing applications and automating workflows, Docker enables apps to be quickly assembled from components and eliminates the friction between development, QA, and production environments. As a result, IT can ship faster and run the same app, unchanged, on laptops, data center VMs, and any cloud.
The main features of Docker are:
Lightweight, portable
Build once, run anywhere
VM - without the overhead of a VM
Each virtualised application includes not only the application and the necessary binaries and libraries, but also an entire guest operating system
The Docker Engine container comprises just the application and its dependencies. It runs as an isolated process in userspace on the host operating system, sharing the kernel with other containers.
Containers are isolated
It can be automated and scripted
Pablo Lalloni on 30 Apr 15"But when Mark Russinovich, Microsoft's CTO for Azure, took the stage at Build 2015 in San Francisco Wednesday morning to demonstrate how containerized microservices applications work in Windows Server. [...] As is his wont, he dove right in to a demonstration of using Docker Build (on a PowerShell command line) to package and deploy an ASP.NET web site as a Docker container. [...] He took only a few seconds to package the web site into a container image, then he ran the package with the docker run command. [...] And then he paused, took the temperature of the room, and may have recognized that Windows developers may have been completely confused by what they were seeing. [...] So Russinovich asked for a show of hands of folks in the room who might have heard of something called Linux. (Don't worry, he's done this before.) [...] He then used a new build of Visual Studio, running in Windows, to publish the container to the Linux host. He then proceeded to debug the running Linux app, including setting a remote breakpoint, from Visual Studio. [...] Without saying so explicitly, Mark Russinovich was obsoleting much of Windows Server before developers' eyes."