Comment by secondcoming

It used be Google Deployment Manager but that's dead soon so terraform.

To roll back you tell GCE to use the previous image. It does all the rolling over for you.

Our deployment process looks like this:

- Jenkins: build the code to debian packages hosted on JFrog

- Jenkins: build a machine image with ansible and packer

- Jenkins: deploy the new image either to test or prod.

Test deployments create a new Instance Group that isn't automatically attached to any load balancer. You do that manually once you've confirmed everything has started ok.