Jason Hoffman of Joyent has written an interesting article, Why EC2 isn’t yet a platform for “normal” web applications.

1. No IP address persistence (they all function as DHCP clients and are assigned an IP). One has to use dynamic DNS services for a given domain.
2. No block storage persistence. When the instance is gone, the data is gone. Yes I know you can send this back regularly to S3, but isn’t that actually a ‘hack’?
3. No opportunity for hardware-based load balancing (which happens to be the key to scaling a process based framework like Rails and mentioned above).
4. No vertical scaling (you get a 1.7Ghz CPU and 1 GB of RAM, that’s it). So like the block storage problem, this hits databases, we run about 32GB of ours in memory.
5. Can’t run your own kernel or make kernel modifications so there’s no ability for kernel and OS optimizations, and no guarantee that they’ve been done.
6. Images have to be uploaded and then moved around their network to find a launching point. This can take several minutes, if not more. Move 100 GBs around a busy gigabit network sometime and see.

What do you do when you have regular traffic spike? Say, for once a month, traffic increases 3 fold for 12 hours after your company sent out the monthly news letter? Your current web server barely copes with regular load. Do you go out to buy 2 more dedicated servers just for that 12 hours in a month? That wouldn’t be too economical paying 2 extra servers sitting there idling most of the time, wouldn’t it?

Judd Vinet of ArchLinux (one of my favourite, btw) has recently written an article to solve this very issue, Web clustering with Amazon EC2, where extra servers are hired from Amazon EC2 on part-time basis to serve surge in traffic. A semi-automated system has been built to make the task of “summoning new servers” much easier, and has been discussed in the article.