Using Memcache on Load Balanced Servers

Question

I'm using Rackspace Cloud Servers. I have installed NGINX with PHP and Memcache.

When the Web server is approaching capacity, I plan to clone the server, and then add a load balancer on top of it ie two servers with one load balancer managing the traffic between the two. All this is done automatically using the Rackspace API.

However, I'm lost as to what is going to happen to Memcache. I now have two Memcache servers. So the cache will no longer work as expected being that there are now, essentially, two Memcache servers.

Is it possible to just install Memcache on a unique server and then have my main Web server access it, this way when I want to create a situation where there is a load-balancer ie two web servers, they would both be referencing the same Memcache server?

Answer 1

Yes, you can have a single Memcached server and all Memcache clients connect and use it (rather than local installs of Memcached). You can use two Memcached servers if the data inconsistency is acceptable and the cost of calculating any stored data twice is acceptable to you. It'll save you time in the short-term, but ultimately it will probably complicate things.

In relation to Rackspace, make sure you're using the private direct IP address Rackspace gives you to network across machines instead of the external WAN IP. This will be faster, more secure, and won't count against your bandwidth allocation.