Well, it is possible, but not recommended (at least the last time I looked it up). The projects can see/change the cache of other projects. I switched to Redis, where I have an instance per project. Maybe it has changed in the meantime, my information is kinda old .. Since redis performed much better than memcached, I never looked back See for examlpe: https://security.stackexchange.com/...use-memcached-in-a-shared-hosting-environment
Yes It is possible to do that. Basically, Memcache is a memory store space. and you can run memcache on one or more servers. Hope this will help you. Thank you.