Now that we know about the various types of virtual machine instances that are available to us and how we can specify that in app.yaml using the instance_class directive, let's take a look at the scaling options that we have in Google App Engine. There are basically three types of scaling at our disposal:
Manual scaling
Basic scaling
Automatic scaling
Automatic scaling is the default type of scaling at work when you don't specify one. Let's take a look at each of these types of scaling.
When you opt for manual scaling for your application, these instances will run continuously forever until you shut them down yourself from the admin console. You have only one configuration parameter when specifying manual scaling, and that is the number of instances that you want to run. To specify manual scaling, use the following in the app.yaml (or in the other configuration files, as we'll explore when going through modules) like this:
instance_class: B4
manual_scaling:
instances...