Security & Scalability

[eluser]graf[/eluser]
I'm about to embark on my biggest/hardest project yet...
My previous 'big' application i built on codeigniter... as of now the site has about 60k registered users and about 350 average daily... codeigniter seems to be handling this traffic well.

My next project is going to be a social network... the blueprints include chat/blog/IMs utilizing extensive ajax.

For most I have to worry about security as the site will be controlling/managing confidential data: (What direction should i go in as far as session management, i'm willing to invest alot of time to make sure this is secure)

Second, the total amount of people registering for the site is estimated at around 2.5k the first month (current traffic) and potentially growing to 5k new accounts per month after 8m-12m marketing tactics. Can codeigniter handle 600k hits a month?

As far as the chat server goes.. i've built winsock chat servers in VB and i've directed PHPLive a few times for inner workings but what would you guys recommend (direction) for accomplishing this task inside of the codeigniter system?

I've been told to switch to drupal... but... BLAHHH.. i <3 codeigniter... i'd love to stick with codeigniter forever.

Thanks for your thoughts and recommendations.

James

[eluser]hooflung64[/eluser]
While a lot of work has been done with session management I still prefer to use $_SESSION directly in my controllers.

As for the ability to handle 600k hits a month that is not really a codeigniter issue. That is your application architecture at fault if it cannot. You will probably need to add memcached so that your server(s) can use a multitude of machines for content/query caching and add eAccelerator for compiling your scripts into bytecode locally on the webserver.

PHP only does what you ask of it