Upgrade to Apache 2.4 and AddOutputFilterByType issue
For quite some time now, we have been using Apache module mod_deflate to gzip some static content served by Apache automatically:
If you upgraded from Apache 2.2 to 2.4, you will notice error in your apache log:
Invalid command 'AddOutputFilterByType', perhaps misspelled or defined by a module not included in the server configuration.
To fix this, enable mod_filter and restart Apache. mod_filter is required in 2.4, although in 2.2 was not the case.