I have a dynamic php (Yii framework based) site. User has to login to do anything on the site. I am trying to understand how caching and CDN work; and I am a bit confused.
Caching (memcache):
My site has a good amount of css, js, and images. I've been given to understand that enabling caching ("memcache"?) will GREATLY speed up my site. But this has me confused. How does caching help? I mean, how can you cache something that's coming out of DB for each user separately? For instance, user-1 logs-in, he sees his control panel. User-2 logs-in, user 2 will see their control panel.
How do I determine what to cache? Plus, how do I enable caching (memcaching)?
CDN:
I have been told to use a content delivery network like CloudFlare. It is suppose to automatically cache my site. So, when my user-1 logs in, what will it cache? Will it cache only the homepage CSS, JS, and homepage images? Because everything else requires login? What happens when user logs-out? I mean, do "sessions" interfere with working of a CDN?
Does serving up images via CDN reduce significant load on my server? I don't have much cash for getting a clustered-server configuration. So, I just want my (shared) server to be able to devote all its resources in processing PHP code. So, how much load can I save by using "caching" (something like memcache) and/or "CDN" (something like CloudFlare)?
Finally,
What would be general strategy to implement in this scenario for caching, cdn, and basic performance optimization? do I need to make any changes to my php-code to enable CDN like CloudFlare and to enable/implement/configure caching? What can I do that would take least amount of developer/coding time and will make my site run much much faster?
Oh wait, some of my pages like "about us" page etc. are going to be static html too. But they won't get as many hits. Except for maybe the iFrame page that will be used for my Facebook Page.