We have several servers running various versions of Apache and PHP. When one or other of them needs to be upgraded, I can't seem to think of a way to do it without losing the server for a while. The problem is that PHP needs to be compiled against an installed Apache, and a newly upgraded Apache throws errors if the existing PHP module is not compiled against it.

This means that, when you make install the newly compiled upgrade of Apache, you get a bunch of these in the error_log whilst the server refuses to serve:

[Wed Jan  4 12:08:59 2006] [notice] child pid 25162 exit signal Segmentation fault (11)

But only now can you compile PHP and install it, and then restart Apache.

You can shut down the server during this of course, but that puts you with a broken site for a bit...

Update: reading helps I found out to compile mod_perl using apxs. Also played around with mod_ssl - $300 for a certificate! Oi vey...