elastic8

Maybe i'm gonna write something comprehensive later on this topic ( because i have to do some reading on the topic), but
in the meantime this is a good article on mysql replication and the new possibilities.
Other cool stuff you can do .. when popping up multiple instances because of your site being slashdotted you could do basic load balancing using round robin dns with small ttl values for your dns entries (so you can add and remove hosts on the fly and have the updates taken into account). The dns part is fairly simple to do.

You've got to figure out what is the best thing for you when you have to fetch part of your content from a database (eg: mysql ) so replication is handy here if you want to sustain multiple instances that are serving http content and need to do lots of queries to the database.