I have been a writing a draft of this issue for the past 2 weeks, mostly because I'm not sure how to communicate the problem :)
I can confirm that there is definately a problem when transferring virtual servers across hosts though, I'm just not sure what the exact problem is. There are no errors in the logs so I can only communicate the symptoms I'm seeing and hope that you guys know about the issue, or someone else can reproduce it.
The details of the transfer:
Operating system: Debian Linux 8 Perl version: 5.020002 Path to Perl: /usr/bin/perl BIND version: 9.9 Apache version: 2.4.10 PHP versions: 5.6.30 MySQL version: 5.5.55-0+deb8u1
Operating system: CentOS Linux 7.3.1611 Perl version: 5.016003 Path to Perl: /usr/bin/perl BIND version: 9.9 Apache version: 2.4.6 PHP versions: 7.0.18 MySQL version: 5.5.52-MariaDB
Following the server transfer, and the nameserver update, everything appears to work 100%. In my case, all my virtual servers are running WordPress. Once the nameserver change is effective I can do (almost) everything in WordPress on host 2 that I could do on the original server without a problem.
However there a few issues. These are the high-level descriptions of the things that do not work correctly.
Preview website. I think the transfer might be the cause of an issue I had logged previously (https://www.virtualmin.com/node/51969)
I cannot remotely manage (via MainWP) any WordPress site that has been transferred, while I can manage servers that are created directly on host 1 or host 2. No logs are created for the many different MainWP errors I get. Most errors are about HTTP body format etc. If helpful, I can send screenshots.
Part of the transfer process is to automatically create a server alias so that the server can be previewed before propagation. This happens whether creating a virtual server normally or via transfer. The format of the alias domain (eg mywebsite.com) is: mywebsite.host.host2.com The issue I'm seeing is that I cannot access that alias domain at all on transferred servers, but I can access them with servers created on the host directly.
When I transfer servers, all settings of servers on host 1 are left as is, including Let's Encrypt SSL and Wordpress etc. when creating a virtual server on host 1 or 2 I can do everything perfectly, preview website works whether or not I have SSL redirects, and I can access the alias as would be expected.
During troubleshooting, I have tried the following:
After the virtual server on host 1 is transferred to host 2, I removed all scripts and SSL and then reinstalled. No change, which tells me this is an issue with the transferred virtual server itself.
I also tried to create a new virtual server on host 1 (nothing installed, just a clean virtual server) and then I transfer it to host 2, install WordPress and SSL - all the same issues occur. Confirms that this is a virtual server transfer issue, or differences in server templates, software versions causing issues.
Please advise what additional information I can send to troubleshoot this further?