I have an app that has been running on the old Python 2.7 App Engine platform for a few years. It gets very light traffic and usually costs $1 or $2 a month, mainly for datastore read ops.

Suddenly this month there was an additional $11.65 charge for "frontend instances". I've searched the dashboard, documentation, and my configuration files trying to figure out what this means. I still have no idea where it came from or how to stop it, short of turning off the app.