Getting HTTP/2 Working on Apache

Solution 1:

Oh for goodness sake - why do I almost always figure stuff like this out AFTER I post the question. Oh well - hope this helps someone else.

The answer lies in the error log:

[Thu Aug 24 17:55:09.795729 2017] [http2:info] [pid 16949] AH03090: mod_http2 (v1.10.7, feats=CHPRIO+SHA256+INVHD+DWINS, nghttp2 1.24.0), initializing...
[Thu Aug 24 17:55:09.795846 2017] [http2:warn] [pid 16949] AH10034: The mpm module (prefork.c) is not supported by mod_http2. The mpm determines how things are processed in your server. HTTP/2 has more demands in this regard and the currently selected mpm will just not do. This is an advisory warning. Your server will continue to work, but the HTTP/2 protocol will be inactive.
[Thu Aug 24 17:55:09.827124 2017] [mpm_prefork:notice] [pid 16949] AH00163: Apache/2.4.27 (Debian) OpenSSL/1.0.2l configured -- resuming normal operations

So there we go - just use 'event' or 'worker' MPM instead of prefork.