[tra3]

The primary benefit of containerization is isolation. Before docker, you'd drop all your code on a shared host so you had to manage your dependencies carefully. Specifically I remember having to fight with mysql gem a lot to make sure that there no conflicts between installed versions. With docker, you build your image, test it and ship it.

[kenhwang]

We had vm-per-app before docker, so it was still build the image, test, and ship, but it actually had everything it needed inside the vm.

Docker helps with the portability due to it's ubiquitous it is now, but it's not like the vm requirement went away, the docker image still generally runs in a vm in any serious environment, and a lot more attention has to be paid to the vm:docker pairing than the previous hypervisor:vm pairing.

[boredtofears]

I haven't shipped to a shared host since the 00's. We deployed to isolated VMs a decade before docker.