App Engine stuck at two instances at idle?

[Zip Zit]

I'm a first time user for Google Cloud.   I'm a software developer investigating the use of Google Cloud for a customer.  I'm trying to figure out how much different stuff costs before committing to a design.  Frankly the free tier got me interested in using Google Cloud.  Customer will be starting small, but wants the flexibility to grow in the future.  

I built a simple test app using the instructions for the Bookshelf Tutorial App at https://cloud.google.com/nodejs/tutorials .   I did this two or three days ago.  I've probably had ten hits/ submissions to the site.  Nothing fancy.  

What I'm trying to understand is pricing.  As I look at my billing summaries (Google Cloud Platform --> Billing --> Transactions --> Detailed Transactions View) , I see the biggest charge by far is  "App Engine Flex Instance Core Hours."  That had me wondering.  I doubt if I used the site for more than 20 minutes total.  

Next step is to go to Google Cloud Platform --> Dashboard --> App Engine --> Go to App Engine Dashboard. When I get there, I see a graph.  Select All Versions, Instances and then an appropriate time interval... in my case, lets use seven days.  Yup, I see a baseline of 2 instances, with a short pop up to four (which corresponds to my testing the site...) .  

But what's up with those two instances at idle? Seems expensive for doing nothing.  I would have thought there should be zero instances at idle.  Or am I just doing this wrong?  

Many thanks.  

[Jordan (Cloud Platform Support)]

Since you are using the Node.js runtime, you are deploying your application to the App Engine Flexible environment. By default, the minimum number of instances for any GAE Flex app is set to '2'. This is why you are constantly seeing two instances serving your app. 

You can edit your app.yaml to deploy your app with a lower 'min_num_instances'. Note that the hard minimum limit for App Engine Flexible apps is '1'. You can always stop or delete a version to completely removes its instances.

If you instead wish to use a GAE Standard environment supported runtime, the hard minimum limit there is '0'.