As day by day you lost track of your Apache configurations and Apache modules. Here is quick shell/bash command to check which modules are loaded and compiled with your current Apache version.

httpd -l

Output will be something like this:

Compiled in modules:
core.c
mod_authn_file.c
mod_authn_default.c
mod_authz_host.c
mod_authz_groupfile.c
mod_authz_user.c
mod_authz_default.c
mod_auth_basic.c
mod_include.c
mod_filter.c
mod_deflate.c
mod_log_config.c
mod_logio.c
mod_env.c
mod_expires.c
mod_headers.c
mod_unique_id.c
mod_setenvif.c
mod_proxy.c
mod_proxy_connect.c
mod_proxy_ftp.c
mod_proxy_http.c
mod_proxy_ajp.c
mod_proxy_balancer.c
mod_ssl.c
prefork.c
http_core.c
mod_mime.c
mod_status.c
mod_autoindex.c
mod_asis.c
mod_suexec.c
mod_cgi.c
mod_negotiation.c
mod_dir.c
mod_actions.c
mod_speling.c
mod_userdir.c
mod_alias.c
mod_rewrite.c
mod_so.c