My amateur radio club, https://www.dhars.org.uk/ is on the same server, but uses a different IP address, as I was under the impression it was better to use different IP addresses.
My web server is
Server version: Apache/2.4.25 (Debian)
Server built: 2018-11-03T18:46:19
The operating system my web server runs on is
Linux localhost 4.9.0-6-amd64 #1 SMP Debian 4.9.88-1+deb9u1 (2018-05-07) x86_64 GNU/Linux
I have a virtual private machine, with root access. I don’t use cpanel - just the command line.
Since I have different IP addresses for the two domains, the Virutal hosts definitions look a bit different
Would it be better to have a different IP address for each domain - or at least keep the important sites on their own IP address? I can get as many IP addresses as I want, but they all have to be paid for, and that is not an intransigent amount of money each month.
In my opinion, the only advantage of a single IP address per hostname is the benefit of very old browser support.
Modern browsers us server name indication to support multiple hostnames behind a single IP address. On the Wikipedia page you can see a list of clients and from which version SNI is supported.
As for the redirect: your Apache configuration for the .com TLD is incorrect. You have the .co.uk certificate enabled, which gives rise to SSL errors because of the hostname mismatch. You need to enable the correct SSL certificate. Even when accepting this erroneous certificate, there is no redirect indeed. It’s missing.
You shouldn’t even need two IPs for that – if you have one IP and Apache lets you set that one certificate as the default for clients that don’t support SNI.
Also, millions of websites don’t try to maintain compatibility with clients that old. Plus you’d have to enable older cryptographic algorithms that are sometimes off by default, and test your CSS and JavaScript and so forth…