Because Magento 2.4 needs ElasticSearch, are there any security implications in running it on a shared hosting environment ? Do Magento Devs recommend any specific configurations ? And what it will happen if two customers decide to use same index prefix ? As a shared hosting provider with hundreds of Magento installations, we simply cannot get in touch with every client to make sure that they are using different index prefix. Even if we do announce it for current customers, a new client that simply ignores a notification might end up using same index prefix.
I don't believe that it make sense to run Elasticsearch in a shared hosting environment, especially with the conflicts that may occur, the high memory requirements of Elasticsearch along with the security and privacy risks involved.
You may want to consider either getting your clients to upgrade to their own environment to run Magento 2.4 or consider have them installing a third-party module to restore the MySQL search capability.
Can you please tell me if search will break if two magento sites will use same index prefix in elasticsearch? Or if any other issue will pop up. Asking in case we will provide a virtual server with multiple magento installation for a single client.