> Docker was the first viable containerization technology on Linux.

No it wasn’t. Docker was late to the party even for Linux (and Linux was late compared to every other “UNIX”).

OpenVZ was around for years before docker. Its main issue was that it required out-of-tree kernel code. But there were some distributions that did still ship OpenVZ support. In fact it’s what Proxmox originally used. And it worked very well.

Then LXC came along. Fun fact, Docker was originally used LXC itself. But obviously that was a long time ago too.

I’ve used both OpenVZ and LXC in production systems before Docker came along. But I’ve always preferred FreeBSD Jails + ZFS to anything Linux has offered.

Not really, OpenVZ was/is really quite good, it was just hampered by the fact it requires out of tree modules. LXC has also always been very usable (Docker even used it for several years) but it was IMHO too focused on the VM-like management scheme that Zones and Jails had.

Docker's killer selling point was that it solved a very common and specific developer problem, not that it provided operational improvements over the state of the art on Linux. From an operational perspective, Docker has generally been a downgrade compared to LXC. (I say this as a maintainer of runc, the container runtime that underpins Docker, and as someone who worked a lot on Docker back in the early days and somewhat less today.)