The cost saving from reserving an EC2 instance is quite dramatic. This morning I moved two web servers to reserved instances and am dropping my hosting cost by 64% for those servers. There isn't actually any effort required in moving your on demand EC2 instance to a reserved instance. The only actual change is a billing change, you don't need to do anything in your instance configuration. The only important thing to remember is that you're reserving an instance in a particular availability zone. The billing effect will only apply to instances launched in the same availability zone. Amazon will apply the discount of having a reserved instance to your invoice automatically. They provide quite extensive documentation on reserved instances on their site ( here ).