Steps for moving an existing static website to gcloud (GCS bucket with an LB in front of it)
Some of this is covered in the gcloud docs here - I add in the part about safely migrating your SSL cert.
This assumes you have an SSL cert chain and private key, similar to those issued by letsencrypt. In my case I'm moving from a VM running nginx and letsencrypt certs.
First, set up the bucket as described in the above docs, or do the auto update from hugo thing I describe in this gist
Make sure access is open: gcloud storage buckets add-iam-policy-binding gs://my-static-assets --member=allUsers --role=roles/storage.objectViewer