Really, basically every server I see is either Ubuntu or Centos. Very few Debian. With containers is different, who packaged the container for a given service wins. Example: Elastic uses Debian for their docker images on docker hub.

See also the results of this survey https://brashear.me/blog/2015/08/24/results-of-the-2015-slas...

It begins to be old but this section is telling "Which Linux distribution do you primarily use on your server computers?"

    Distro  #resp  %resp  prev year
    Ubuntu  633    34%    27%
    Debian  539    29%    31%
    CentOS  214    12%    15% 
    ...

Not a large poll but I didn't find anything better in a quick search on Google.

Doesn't that poll contradict your "very few Debian" statement?

In part yes, but I'm a developer so I'm probably seeing those new Ubuntus that made Ubuntu overtake Debian. If I were an op I'll probably have a more balanced view.

Furthermore the sample is relatively small and my own sample is at least 100x smaller.

CentOS is in a tricky position with regard to ALPN/http2 support--there's absolutely nothing on the horizon. A continuing shift to Ubuntu in the webserver space is almost certain in the mid-term.

How many companies are moving to ALPN/http2? AFAIK, they're still pretty fringe.