One of the most important features of App Engine is its ability to scale a number of instances. We have a choice regarding the level of automation we want to use. App Engine offers three options, as follows:
- Manual scaling: In this setup, you specify the number of instances that will run, no matter what the load will be. Since the instances keep the memory state, it can be used for applications that depend on it.
- Automatic scaling: In this setup, a number of instances depend on the request rate, response latencies, and other application metrics. It also allows you to specify a number of instances that should always run independently of the load.
- Basic scaling: In this setup, an instance is created when a request is received by the application. The instance will be shut down when the application becomes idle. It can be used for apps that are driven by user activity.