Wordpress and Caching.

I hope this will help some one any advise is welcomed.

I have a VPS with 32g’s of ram, and 8 CPU’s. I use CWP on it to host 24 accounts for in-house domains I manage all running WordPress on low traffic websites. My main site has 17 active plugins and three that I activate on a per / use basis for wp-admin tasks only and it has the most traffic. So I have been using Nginx & Varnish & Apache using WordPress as the Varnish default vhost template.

I am developing a WordPress Multi-site that I hope will gain traction. I have opened it up for registration for sites and memberships. So for the first time in years I looked at tweaking the server now before it grows larger and becomes more active with visitors / members.

For 3 years now I have not been using any caching plugins for WP except for the Redis official plugin. At one point a couple of years ago I enabled cache on all WP installations. Before too long I had caching errors and it happened again using W3 Total Cache plugin again selecting redis for object / DB caching.

The issue is that I would be and some visitors served another domain / wordpress site on the this same server.

Security became a concern as I have /wp-admin/ rewritten to /”secret-admin”/ across all my sites on the server and I was getting served up login urls @ another site. As admin using the brave browser it is a struggle to clear out the cache on the client side and visitors like me and crawlers might have to wait a while for it to expire locally. On any event I loos site traffic and it sets of the search engines and browser warnings.

I did some quick research and by trial and error have come to the conclusion Opcode (APC-APCu) seems to be the right setting for the VPS (KVM).

W3TC suggested that I use Advanced Disk Caching option for a shared hosting environment - I first tried redis as it consistently gave the best performance gains according to the benchmark testing I did in the plugins initial setup and I thought W3TC would keep it from polluting other WP caches on the server. I tried memchached, it seemed to work well, php-fpm and mariadb calmed down quite alot. I then reconfigured W3 to use Opcode and so far it has outperformed memecached.

My question is using Opcode (APC-APCu) instead of Advanced Disk Caching the right choice?

Technically each WP installation is in a shared server environment with different cwp user accounts and W3TC says that disk caching is the best option.

Am I naive in thinking Opcode (APC-APCu) is safe and or the right choice given all the shared hosting sites are in house?

Again I hope this helps someone and if you have feed back I look forward to hearing it.