I was wondering what the difference between an instance and an instance group are.
Can anyone explain the difference to me?
Why can we use Autoscaler with an instance group and not with a instance
In GCE, An instance is a single virtual machine that you can customise (CPU, network, endpoint, disk, etc) and manage by you (shutdown, run, build with new image, etc)
https://cloud.google.com/compute/docs/instances/
An instance is a virtual machine hosted on Google's infrastructure.
Instances can run the Linux images provided by Google, or any customized versions of these images. You can also build and run images of other operating systems.
While an instance group is a collection of the instances above, for management. i.e. I have two groups, slow instances and fast instances.
Autoscaler is something that you can use with Managed Instance Group. This a group that is created by Instance Manager using an instance template.
https://cloud.google.com/compute/docs/instance-groups/
A Compute Engine Autoscaler automatically adds or removes virtual machines from a managed instance group based on increases or decreases in load. This allows your applications to gracefully handle increases in traffic and reduces cost when the need for resources is lower. You just define the autoscaling policy and the autoscaler performs automatic scaling based on the measured load.
Hope it helps. Cheers.