Yeah, I understand that the concept of process isolation has existed for a long time. We used to know them as "chroot jails". cgroups obviously is a feature that has been dormant in the Linux kernel for a long time (until Docker came along and convinced everyone they had to use them, which actually isn't really a point in favor of containerization either: "we depend on this lightly tested feature of the kernel!"). Those things on their own are substantially different from what are today known as containers, a mix of concepts that involves custom daemons, complex network routing layers, bolt-on orchestration components like Swarm/Kube, and all sorts of other voodoo that makes today's understanding of "containers" distinct from historical uses either of the term or the concepts implemented via jails/zones/whatever.