Hosting your app in the cloud is a great idea - give all the hardware problems to some one else. The downside is of course that you have to pay for the privileged. Now Amazon is giving you the chance to pay less - but for less. Micro Instances is a new feature which provides a low cost way to cloud hosting. It's targeted at small businesses and small development projects, but it is also obviously a way to test the water and see if a small idea could grow into something big.
There isn't much new technically. You can have a 32- or 64-bit virtual machine with 613 MBytes of RAM but no local storage. This means you have to boot from Elastic Block Store and use this for any permanent storage the Micro Instance needs.The amount of RAM available is also fairly small and you would need to think carefully about what you were planning to run as an OS configuration.
They are also monitored with the CloudWatch utility and they support auto-scaling. This means that if the load gets too much you can automatically start another Micro Instance or even a bigger VM configuration. Amazon estimates that you can have two Micro Instances running under CloudWatch for the cost of one standard instance.
You can have a Micro Instance for around $0.02 (two cents) per hour for a Linux host and $0.03 (three cents) per hour for a Windows host. It's interesting to note that this prices Windows at one cent per hour if you take the point of view that Linux is free. Micro Instances can be bought on a spot market which sells unused Amazon processor cycles for whatever they will fetch or you can buy a reserved VM for a fixed price and a reduced hourly rate. Clearly working out how much a micro instance will cost is a problem and Amazon have provided a calculator to help. The AWS Simple Monthly Calculator now includes the Micro Instances. For example a Linux Micro Instance running on demand with a 50% utilization per month would cost around $10 per month and adding a modest 1GByte fo EBS storage and some extras brought the cost up to around $12 per month.
Although only designed for low traffic applications - tens of requests per minute - there are lots of situations that fit this pattern, but it seems as if Micro Instances are also a way of Amazon getting users and developers into using EC2. After all, once you are in the sweet shop who can resist buying a little more processor power and some storage, and a load balancer and .... you get the idea.
To sign up for Amazon SNS and other AWS services, visit http://aws.amazon.com.