var gce = gcloud.compute();
var zone = gce.zone('us-central1-a');

// Get all of the instance groups in the project (also available in stream mode)
gce.getInstanceGroups(function(err, instanceGroups) {});

// Get all of the instance groups in a zone (also available in stream mode)
zone.getInstanceGroups(function(err, instanceGroups) {});

// Reference an existing instance group
var instanceGroup = zone.instanceGroup('instance-group-name');

// Add VMs to an instance group (1 or more)
instanceGroup.add([
  zone.vm('my-vm'),
  zone.vm('my-other-vm')
], function(err, operation, apiResponse) {});

// Remove them (1 or more)
instanceGroup.remove(zone.vm('my-vm'), function(err, operation, apiResponse) {});

// Get the VMs from the group (also available in stream mode)
instanceGroup.getVms(function(err, vms) {});