Google App Engine has this item – Discounted Instance Hour – which you can reserve a number of hours per week at a cheaper cost.

Recently, I was looking at the Charge Sent per week, and one of the item is this:

Unused Discounted Instance Hour – Used XXX hours

The item cost a big part of my weekly charges. I was puzzled at first: How did I used XXX hours out of an item that said is unused?

Then I went to my Billing Settings, and saw this:

Discounted Instance Hours: YYY Hours

Committing to a number of instance hours for a weekly billing period in advance can 
help lower your bill. You will be charged $0.05 per hour for the hours you commit to here, 
even if you don't use them during the billing period.

I have set YYY hours per week as a Reserved Discounted Instance Hours.

Even if I don’t use them, they are charged!

Lesson Learnt

At times, you should monitor the weekly usage.

If the Unused Discounted Instance Hour is very high (much higher than what is being used), then you should adjust it from Billing Settings.

I have wasted quite some money paying for instance hours that I didn’t use..

(I set the reserved instance hours very high initially because there was a period of peak, but now it has gone down, yet I didn’t adjust..)