From /usr/share/foreman/vendor/ruby/2.1.0/gems/fog-google-0.1.0/lib/fog/google/requests/compute/insert_server.rb:

          # ExternalIP is default value for server creation
          access_config = {'type' => 'ONE_TO_ONE_NAT', 'name' => 'External NAT'}
          # leave natIP undefined to use an IP from a shared ephemeral IP address pool
          if options.key? 'externalIp'
            access_config['natIP'] = options.delete 'externalIp'
            # If set to 'false', that would mean user does no want to allocate an external IP
            access_config = nil if access_config['natIP'] == false
          end

So resource.networkInterfaces⁰.accessConfigs⁰.nat should be undefined if one wants a ephemeral IP assigned?

'resource.networkInterfaces[0].accessConfigs[0].natIP': 'true'. Must be an IP address

also if I fiddle with subnets and interface names or provide internal IP then it gives someting like no subnetwork defined for custom network.

I have spent two days on it. This problem just doesn't let me go forward. Possibly I shoud try to create a new gce instance using gcloud or web console: manually install puppet agent/salt-minion on it and then add it to foreman.

Do not have a clue as I just discovered foreman a few days ago.

A few hints about workaroud might be helpful.