How do you rewrite/recode a website to be scalable? [closed]

Question

How do you rewrite a website to be scalable?(traffic) I work with mainly PHP and some Ruby on rails and i know its a generic question. I'm just looking to increase my knowledge so any advice would be useful.

Thank you in advance ;-)

Answer 1

This is a quite wide question, and it's going to be pretty difficult to give you a definite answer -- but a couple of ideas :

• First of all, do not pre-optimize !
  • Make sure your application works ; that's the most important thing.
  • And, only when it becomes necessary, start optimizing.
• PHP by itself generally scales well :
  • Add a couple more Apache+PHP servers, load-balance your users
  • And this tends to work really easily
• Filesystem doesn't scale that well / that easily :
  • it's not shared accross servers
  • sharing filesystem (with NFS, for instance) can sometimes cause problems.
• The database is generally the hardest part, when it comes to scaling :
  • Having more than one "write" server is hard
  • Having more than a couple of "read" servers, generally using replication, can become a pain for maintenance
  • You'll have to think about sharding, one day or another, if replication is not enough.
• Use lots of caching : the more cache you can use, the less queries you'll make to the DB, the better it'll be
  • memcached is great, and scales well : just add a couple of servers, and you get a couple of more GB or memory in your caching-cluster
• Using a reverse-proxy, so your Apache+PHP servers have less work to do, helps too.

And a quick couple of links that might give you some ideas :

• Database Sharding at Netlog, with MySQL and PHP
• Scaling WikiPedia with LAMP: 7 billion page views per month

Answer 2

One tip - cache data using memcached or an equivalent, instead of querying the database directly.

Also, the most difficult part of scaling is moving beyond a single web server. Once you can scale to two web servers, you should not have much trouble scaling to many more.