In the docs for GKE it says all nodes (currently) have the same VM instance. Does this refer to the underlying machine type or the OS image (or both)?
I was assuming it was just the machine type (micro, small,.. etc) and Google layered their own image with infrastructure on top of that (e.g. kubernetes).
If this is the case what image does Google use on GKE? I was thinking it may be CoreOS, since that would seem to be a good match, but I am not sure.
I'd like to set up staging machines with the same image as production... but perhaps we don't need to know this or it doesn't matter what is used.
All nodes in the cluster currently have the same machine type and OS image. By default, the machine type is n1-standard-1 and the image is a recent container-vm image.
If you use gcloud to create your cluster, both settings can be overridden on the command line using the --machine-type and --source-image options respectively (documentation).
If you are using the cloud console to create your cluster, you can specify the machine type but not currently the source image.
Be aware that if you specify a different source image, you may not end up with a functional cluster because the kubernetes software that is installed on top of the source image requires specific underlying packages to be present in the system software. If you want consistency between staging/prod, you can use
gcloud container clusters describe <staging-cluster-name>To see what image is being used in your staging cluster and ensure that you end up with the same image for your production cluster.