Docker is an image based container technology. Containers have been around for many years, talk to any Solaris SME and they will tell you they’ve been using containers for several years. However, containers have been available in Linux as well, before the advent of Docker. Linux containers (LXC) is a operating system level method of running multiple isolated Linux systems on the same host (sharing the same kernel). This is much like Solaris containers / zones which use the same kernel (I think on Solaris they call it Kernal?)
The downside, as we had great pleasure in pointing out to Solaris SA’s some time back, is that zones run on the same physical hostname, using the same kernel, so if something happened to that kernel, all zones / containers were in clobbered. Fast forward several years and we’re in the same boat.