EnterpriseDB announced that their PostgreSQL based database offering will be available inside of Amazon's EC2 cloud. Some details are available from Information Week

Hosted PostgreSQL services have been around for years a database cluster that can rapidly scale is less common. The appeal of Amazon's compute cloud is that you can start of small with low resource utilization and have an application running in the cloud fairly inexpensively. You can then devote more resources to the application on an as-needed basis. EC2 also allows you to keep costs down during less busy times of the month (or year) by paying on a metered basis. Traditionally coming up with a way of scaling the database tier up quickly requires careful application architecture to make the application compatible with replication or partitioning based solutions. Oracle's RAC offers an alternative approach but the cost of scaling a RAC cluster from 2 nodes to 20 in a short period of time exceeds the cash most web companies have on hand.

What I'm interested in seeing is what constraints EnterpriseDB/Elastra puts on the application and database. Elastra claims their cluster is 'infinitely scalable', and EnterpriseDB claims their database is going to be transactional. Over the years I've looked into a lot of ways of clustering databases, especially PostgreSQL based ones, and it always comes down having to accept some set of constraints, limitations often involving trading off transactional consistency versus performance. It will be interesting to see what trade-off's this solution involves and how it works.