Scalability tips please.

[codebyren]

I've been doing heaps of reading on what goes on behind the scenes once a site gets too big/popular for shared hosting, dedicated hosting, multiple server hosting and so on...

 

Now that I have some limited knowledge, I can't seem to keep it out of my head while working on my current site. What I would like to know is how experienced people handle this sort of stuff within their code? I'll take any and all advice/tips.

 

Some of my concerns are:

 

• how do you link to all your files/images when you know that one day those links could all become invalid if you setup a separate file server? Surely the paths may change? Do you setup links like <a href='$file_root/images/whatever.png'></a> and then just change the value of $file_root when you move servers etc.? Will this even work?
  
• Do you save all session data in a database? Having multiple servers would mean that session data would be lost if a user was jumping between servers otherwise? Is there some other way I'm missing? Surely you wouldn't use cookies...?
  
• If you had to have redundant file servers to ensure speed... how the heck would you keep data synchronized between them? When a user uploads a file, do you just copy it to multiple servers right there and then? I'm not even going to think about how you would allow your web server the right to write to multiple other file servers' hard disks?
  

 

If you have confronted any other problems in your own website developments, I'd really like to hear about them. Thanks for reading.

 

Also, if anyone can share some good resources for where to learn about this sort of stuff, that would be appreciated. I've had a look at www.highscalability.com which is enlightening - and intimidating - it's quite easy to get lost in their case studies because so many different terms and softwares are referred to. I don't really know where to start...