Since 2006 first as part of the Ottawa Linux Symposium and later as part of the Linux Plumbers Conference we had yearly in person meetings.

We had public discussions on the Linux Kernel mailing list and later on the containers list.

It was a collaborative effort from vserver, openvz, IBM, and Linux Networx, and google. I think those were all the original groups, my apologies if I have forgotten someone.

After Docker made a splash I occasionally asked other developers if they had any contacts at Docker. To the best of my knowledge we never received a bug report, or a feature request. No one from Docker ever showed up at any of our meetings.

I know at one point I wanted to let someone know that Docker they were holding the pieces wrong when it came to security.

Eventually I think one of the OpenVZ guys wound up working for Docker for a time. But that was quite late in the timeline.

I was passing through RedHat about the time of the spat you mention. My impression at the time was that Docker never worked well with anyone, and after some frustrations trying to cooperate the RedHat userspace folks decided it was easier to get a real standard without Docker.

At that point I had gotten the unprivileged user namespace support into RedHat's kernel and changed a lot of minds about it's utility.

I don't remember Docker ever picking up unprivileged user namespace support and as a result was a security disaster waiting to happen.

It felt to me like Docker treated the userspace API for containers like most folks treat the POSIX API. Fixed in stone. In fact there was a lot of wiggle room, and opportunity to shape things for anyone who was willing to dive deep into the technical details.