What is the best solution to protect communication between multiple servers?

We have a number of Database severs running MongoDB on Debian plus a number of Application servers also on Debian. The db servers hold replicating db clusters, so they need to talk to each other. Application servers need to talk to all db servers (for reasons of fault tolerance). The servers are potentially spread across multiple hosting centers, so we need secure channels between all servers.

We have a central repository of files in say server-1 at /srv/www. Then we have N number of servers as well.

What would be the preferred solution for hosting several physical servers behind a NAT with one external IP? I know Apache can reverse proxy HTTP but if i want to do the same with FTP? Squid seems to be mentioned a lot but i am a little confused if it will work with my set up: A few physical boxes running Ubuntu with Virtualmin and they are all behind a NAT.

Since I've got multiple cPanel servers, I'd like them to share information regarding various security aspects.

I have an extensive network of servers all currently hosted on AWS EC2.

For reasons of cost I plan to gradually migrate to dedicated servers where possible.

So: How can I best combine AWS and non-AWS servers in my network?

I have 2 soon to be 4 servers in rackspace cloud, they are windows 2008 64 bit r2 machines. I am trying to set up a private network with which I can VPN into.

Got a major issue that I need some help with. Here is the situation.

The client has multiple web sites hosted on multiple web servers (virtual machines) running on multiple virtual hosts that connect to a backend domain that have multiple SQL clusters (active / passive) for the multiple websites.

Although Microsoft Windows still dominates the desktop operating system popularity, Linux has become a dominant force in cloud servers and virtual private servers (VPS). Linux is not only a cheaper way to host cloud applications, but it also comes in several distribution flavors.

Customers looking at cloud hosting as a solution can choose from CentOS, Fedora, Ubuntu and Debian.

I will be providing "File-Hosting" service and I need something that works with me along the line and allow the project to expand. At first I was thinking about one big server with RAID 5 as a start-up, but then I thought using multiple servers would be better as it's easier to expand in the future and should be cheaper, but I have absolutely no idea how these servers should/can be linked and if