Docker is more than just chroot. You also need: overlay file system; OCI registry and community behind it, to create thousands of useful images. And, of course, the whole idea of creating images layer by layer and using immutable images to spawn mutable containers.
I don't actually think that you need network or process isolation. In terms of isolation, chroot is enough for most practical needs. Network and process isolations are nice to have, but they are not essential.
A SINGLE regular text file that took regular shell commands and could build the same deployment from scratch every time and then be cleaned up in one command.
This was UNHEARD of. Every other solution required learning new languages, defining “modules,” creating sets of scripts, or doing a lot of extra things. None of that was steezy.
I was so sold on Dockerfiles that I figured that even if the Docker project died, my Dockerfiles would continue to live because other people would try copy the idea of Dockerfiles. Now it’s been 10 years and Docker and containerization has changed a lot but what hasn’t? Dockerfiles. My 10 year Dockerfiles are still valid. That’s how good they were.
process isolation is less prominent
The one thing people really seem to miss on them is like, contrary to popular belief you dont need a whole OS container there, minimal distroless containers work just fine with systemd-nspawn similar to as they would on docker.
Much of the technology was there, but Docker was able to achieve a critical mass, with streamlined workflows. Perhaps as much a social phenomenon as a technical one?
The big pain with jails for me was the tooling. There was a number of non-trivial steps needed to get a jail that could host a networked service, with a lot that could go wrong along the way.
Sure a proper sysadmin would learn and internalize these steps, but as someone who just used it now and again it was a pain.
Way down the line things like iocage came along, but it was fragile and not reliable when I tried it, leading to jails in weird states and such.
So I gave up and moved to Linux so I could use Docker.
Super easy to spin up a new service, and fairly self-documenting as you just configure everything in a script or compose file so much less to remember.
Initially in a VM on Bhyve, now on bare metal.
It feels a bit sad though, as jails had some nice capabilities due to the extra isolation.
The effort to introduce the concepts to the mainstream can’t be understated. It seems mundane now but it took a lot of grassroots effort and marketing to hit that critical mass.
