Hidden usage of frontend instance hours

[Diego C.]

Hello.

I have a single service running on App Engine. It's a very-low-traffic website, so I've set it to always have 1 instance running, to avoid lengthy cold starts when someone does visit. It's been running with no problems for a couple of years or so. It always stayed within the free tier. I haven't made changes to it in at least several months.

However, since around mid-March, I've been getting charged for extra instance hours. I've checked the console and everything seems normal. The instances chart shows a straight line on 1, with occasional spikes to 2 which last for maybe five minutes every couple of hours or so, which is normal due to restarts and such, and certainly doesn't seem enough to go over the 28 free hours per day. Right now, for example, it says that I've used 19 hours today, and that the quota will reset in 5 hours, so 24 hours total.

And yet, I keep getting charged. Not a lot, it adds up to maybe 3 or 4 dollars a month, but still, I don't know where it's coming from.

Did App Engine change something about how hours are billed around mid-March? Any ideas on how to check what's going on?

Thanks!

[Ernesto Contreras Pinon]

The documentation shows that when instances are increased, instance time is accrued for 15 minutes after the last request to the instance. This could explain a possible accruing of cost that adds up per month. You could try setting an upper limit of 1 instance, so that if an additional instance is created automatically by App Engine, it does not use up instance time. Do you see other costs that might be also adding up from related services? You can filter the billing report table for your project to see detailed costs of your usage for App Engine.

[Diego Crapper]

Hello, Ernesto.

Thank you for your reply.

If I remember correctly, setting min_instances = 1 and max_instances = 1 created problems when I tried it. I assume it's a problem when Google needs to move the app to a different server, update the underlying software and such.

Regardless, I haven't made any changes since November 3, 2021, and the billing issues only began last month. There hasn't been any noticeable increase in traffic, so what changed?

This is my billing report chart:

Thanks again.

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