Add mod_remoteip to all Apache installs

[preaction]

Most of our sites are behind Fastly CDN cache, which means that most of our sites' access logs show Fastly's IP address, not the real address of the user who is using our site. If we want to then block access to people abusing our site, we need to know their real IP address.

Apache has a module that will show us their IP address: mod_remoteip. In order for this to work, we need to set up some configuration (in the file /etc/apache2/mods-available/remoteip.conf):

RemoteIPHeader X-Forwarded-For
RemoteIPTrustedProxyList /etc/apache2/proxy.list

We also need a cron job to update the /etc/apache2/proxy.list file with this command:

curl -s https://api.fastly.com/public-ip-list | jq -r '.addresses | .[]' > /etc/apache2/proxy.list

Once these two things are in place, we can enable the module using a2enmod remoteip.