Using memcache as a session store?

Question

I currently have a huge problem. Two days ago my site running on one server was too much, so I purchased two more and had them clustered (rsync and load balanced).

I then start noticing that a user would hit server-1 and then on the next request hit server3 but that their session was still on server1 instead of server3 and they were no longer logged in.

I was recommended to use memcache for session stores.

My script already uses $_SESSION.

• Can we get memcache installed and enable session handler support and set session.save_handler = "memcache" to force php to use memcache?

• Is there any application programming that needs to be done to use memcache?

• Will this solve my session between server issue?

• Are the session stores stored on all the servers when they are created or is one like a master memcache server?

I'm using the codeiginiter framework

Answer 1

Please read dormando's post.

Answer 2

You would need to set up memcache to run on one of the servers and have all of the servers use that same memcache instance for the sessions. Otherwise, if they each run their own memcache instance, you'll have the same problem as before.

Other than configuring memcache accordingly and telling PHP to use it as your session handler, you shouldn't have to make any changes to your code.

Answer 3

Both of the major memcache PHP PECL extensions have session handlers. Either will require you to install a PECL module before use.

The Memcache PECL extension session handler is enabled with the following in php.ini:

session.save_handler = "memcache"
session.save_path = "tcp://memcacheServerAddressHere:11211?persistent=1&weight=2&timeout=2&retry_interval=10"

The Memcached PECL extension session handler is enabled with the following in php.ini:

session.save_handler = "memcached"
session.save_path = "memcacheServerAddressHere:11211"

Note that the Memcache extension appears to allow more configuration of the Memcache environment.

Answer 4

You want to be careful about doing this. One thing to be careful about is to not host session info with other non-session data. It isn't the biggest deal to clear your cache when it only contains your own site's data but you do not want to wipe out people's sessions along with it.

As long as your are using the same key with memcache you should hit the same server every time. So that issue should go away.