Ask HN: Anybody having problems with costs of Reserved Instances on AWS?

Hi,

since we switched over to using Reserved Instances on AWS for EC2 and RDS we encounter the strange problem that our cost on the first day of the month is _much_ higher than it should be. Then over the month we are billed our normal cost and the RIs as expected - and a few days before the next month starts the cost from the 1st of the month just disappear. This messes a lot with our "expected costs" calculation of course, but also my trust in the numbers in general.

AWS support couldn't really help in the last 4 weeks, so I'm thinking maybe someone else also has or had this problem and has an idea how to fix it. As lots of people here are AWS users, why not try to ask here...

So, does anybody know this problem or have the same?

Thanks.