How to shutdown all dynamic instances in Google App Engine without re-deploying the app?
We had a similar problem - I found that disabling the app in Application Settings and then re-enabling it terminated all 88 instances we had running, without any other adverse effects.
We are running multiple load tests every day against one of our GAE apps. We use the following pattern:

Start a load test and let it run for a few hours.
Look at graphs.
Optionally deploy a new version of our app with performance improvements.
Go back to 1.

Each load test creates a couple hundred front end instances. We would like to terminate those between individual load tests even when we are not deploying a new version of our app.
Is there a way to terminate all dynamic instances? Right now we either have to deploy a new version or terminate all instances by hand.