Anybody working regularly with IaaS providers such as Amazon or Rackspace can recount a personal story of a forgotten instance.

The most dramatic stories are not about a cheap micro instance – my personal story with AWS cost me some US$200 when I missed to turn off an EC2 instance and went for a diving trip to Egypt. I’ve got a number of suggestions that might save you some money.

• Above all, you want to avoid paying for unused resources. Using auto scaling is a great mechanism for running only the required instances, and for example, to scale down at night when fewer EC2 instances are required.
• Often the monthly bill tells you that there something is still running somewhere. Make sure you stop unused resources as quickly as possible. If you know in advance that you want them to be stopped at the end of the day, then use the Unix at command to schedule the termination of the instances.
• Although AWS management console provides dashboards, there is no super-dashboard. Instead, you have to flip through all tabs yourself (starting from from the “S3” tab to “EC2” and all the tabs up until “RDS”). Only after checking all tabs can you be sure you have an accurate overview of the current resources for the selected region.
• Remind yourself that the AWS management console is always displaying resources per region. Once you switch to another region, e.g. from Asia/Pacific to Europe, you will no longer be able to see instances running in Asia/ Pacific.
• The console is sometimes out of sync. When this happens, remember to click on the refresh button so as to avoid only seeing outdated information.
• The command-line tools I introduce later will work with resources for the default region in the US (unless you specify otherwise). Remain vigilant at all times e.g. when working in Europe do not start and then forget an instance in the US.
• Always double check for running instances before engaging in another project, leaving for a sabbatical or a trip around the world.

Be careful and make sure you don’t wast money that is better spend for a fabulous diving trip.

These tips are taken out of my Middleware and Cloud Computing book.

Update as of May 2012:

You can setup billing alerts now for AWS and use SNS to recalculate your auto scaling. See Jeff’s posting on AWS typepad here.