In OS X 10.10 (Yosemite), Apache has been upgraded from 2.2 to 2.4, which includes some significant changes, and the default config file has changed quite a bit. When you install Yosemite, it renames your old config to httpd.conf~previous
, and unfortunately your old one won't work anymore.
To get Apache working again, edit the following files:
Uncomment: