Both Compute Engine and Amazon EC2 support autoscaling, in which instances are created and removed according to user-defined policies. Autoscaling can be used to maintain a specific number of instances at any given point, or to adjust capacity in response to certain conditions. Autoscaled instances are created from a user-defined template.
Compute Engine and Amazon EC2 implement autoscaling in similar ways:
Amazon's Auto Scaling scales instances within a group. The Auto Scaler creates and removes instances according to your chosen scaling plan. Each new instance within the group is created from a launch configuration.
Compute Engine's autoscaler scales instances within a managed instance group. The autoscaler creates and removes instances according to an autoscaling policy. Each new instance within the instance group is created from an instance template.
Amazon's Auto Scaling allows for three scaling plans:
Manual, in which you manually instruct Auto Scaling to scale up or down.
Scheduled, in which you configure Auto Scaling to scale up or down at scheduled times.
Dynamic, in which Auto Scaling scales based on a policy. You can create policies based on either Amazon CloudWatch metrics or Amazon Simple Queue Service (SQS) queues.
In contrast, Compute Engine's autoscaler supports only dynamic scaling. You can create policies based on average CPU utilization, HTTP load balancing serving capacity, or Stackdriver Monitoring metrics.
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