What a delightfully arrogant comment :) This was about ten years ago. At the time, given the constraints, iptables did not have a public, stable programmatic interface, no. Perhaps you used other firewall systems/frameworks. We had to interop with Docker. I don't remember specifics; I do remember going very deep down that rabbit hole.

For what it's worth, the development team, at least in the early ZEIT days, were the most competent engineers I've ever worked with on a team.