I have a working, extremely complex Ubuntu 12.04 LTS server installed as a VPS under a XEN supervisor. It includes database server, Varnish, memcached, VPN (both IPSEC and OpenVPN) and many, many other services including DNS, mail etc (no, I can't split services on 2 servers for now).
Now, I need to change portions of its web pages, change database tables structures etc. etc. I'd like to do that on a "mirror" of that server on a separate, other VPS instance, to be installed maybe as "dev.domain.tld". I'd then proceed updating changes made to the dev machine to the production one.
Is there someone who could give me hints about how to best and quickest do this?
I guess the host provider would create me a 1:1 copy of the instance, but then I can't use it because it'd have the same IP address, the same hostname and such.
Are there utilities or anything to help me perform the needed changes to have two working, separated servers?
I know this is really a broad question but there has to be someone in the world who stumbled upon this issue and found a way to rationally do it.