> Containers existed before, in the form of FreeBSD jails and Solaris Zones. Even earlier, depending on what variant of mainframe virtualisation you are prepar

> Containers existed before, in the form of FreeBSD jails and Solaris Zones. Even earlier, depending on what variant of mainframe virtualisation you are prepared to count. > Were there limitations that made them impractical ? Not being up close with LKML workings, I can only speculate that it's due to Conway's Law. Having a kernel-level concept of "a container" requires changes cutting across a number of subsystems worked on by very distinct groups of people. Cathedral-style development can achieve that kind of a change. The organisation responsible for Solaris saw the vision, worked out what had to be changed to create a uniform mechanism, then changed it. They achieved broadly the same with ZFS. That said, there is container-as-a-runtime, in which I think having a consistent concept a la Zones has enormous value for consistency, security and performance optimisation opportunities. But there's also container-as-ecosystem. More accurately, _images_ are containers, worthy of that name, because they created such a simple way to take advantage of complex low-level APIs.