VirtuBox Redis-cache plugin use Redis for object-cache with the key : site.tld:
I think something may be wrong with this then. After installing Wordpress sites using the Redis attribute of WordOps, I get two different define( 'WP_CACHE_KEY_SALT', entires in my wp-config.php file.
One is clumped together with other SALT and AUTH_KEY entries (with random jibberish for entries).
The second is below that collection of entires and is a duplicate define( 'WP_CACHE_KEY_SALT', entry.
The second one, as you said, does set the wp_cache_key_salt as site.tld
It's actually the first set of random characters that appears in the first wp_cache_key_salt entry that appears in the Redis plugin as the prefix key.
Is all of that correct?
For some reason, having two wp_cache_key_salt entries in the wp-config.php file seems wrong (but I don't know much about this stuff)