func (kd *Discovery) updateServiceTargetGroup(service *Service, eps *Endpoints) *config.TargetGroup {
	tg := &config.TargetGroup{
		Source: serviceSource(service),
		Labels: model.LabelSet{
			serviceNamespaceLabel: model.LabelValue(service.ObjectMeta.Namespace),
			serviceNameLabel:      model.LabelValue(service.ObjectMeta.Name),
		},
	}

	for k, v := range service.ObjectMeta.Labels {
		labelName := strutil.SanitizeLabelName(serviceLabelPrefix + k)
		tg.Labels[model.LabelName(labelName)] = model.LabelValue(v)
	}

	for k, v := range service.ObjectMeta.Annotations {
		labelName := strutil.SanitizeLabelName(serviceAnnotationPrefix + k)
		tg.Labels[model.LabelName(labelName)] = model.LabelValue(v)
	}

	serviceAddress := service.ObjectMeta.Name + "." + service.ObjectMeta.Namespace + ".svc"

	// Append the first TCP service port if one exists.
	for _, port := range service.Spec.Ports {
		if port.Protocol == ProtocolTCP {
			serviceAddress += fmt.Sprintf(":%d", port.Port)
			break
		}
	}

	t := model.LabelSet{
		model.AddressLabel: model.LabelValue(serviceAddress),
		roleLabel:          model.LabelValue("service"),
	}
	tg.Targets = append(tg.Targets, t)

	// Now let's loop through the endpoints & add them to the target group with appropriate labels.
	for _, ss := range eps.Subsets {
		epPort := ss.Ports[0].Port

		for _, addr := range ss.Addresses {
			ipAddr := addr.IP
			if len(ipAddr) == net.IPv6len {
				ipAddr = "[" + ipAddr + "]"
			}
			address := fmt.Sprintf("%s:%d", ipAddr, epPort)

			t := model.LabelSet{
				model.AddressLabel: model.LabelValue(address),
				roleLabel:          model.LabelValue("endpoint"),
			}

			tg.Targets = append(tg.Targets, t)
		}
	}

	return tg
}

func (kd *Discovery) updateNodesTargetGroup() *config.TargetGroup {
	kd.nodesMu.Lock()
	defer kd.nodesMu.Unlock()

	tg := &config.TargetGroup{
		Source: nodesTargetGroupName,
		Labels: model.LabelSet{
			roleLabel: model.LabelValue("node"),
		},
	}

	// Now let's loop through the nodes & add them to the target group with appropriate labels.
	for nodeName, node := range kd.nodes {
		address := fmt.Sprintf("%s:%d", node.Status.Addresses[0].Address, kd.Conf.KubeletPort)

		t := model.LabelSet{
			model.AddressLabel:  model.LabelValue(address),
			model.InstanceLabel: model.LabelValue(nodeName),
		}
		for k, v := range node.ObjectMeta.Labels {
			labelName := strutil.SanitizeLabelName(nodeLabelPrefix + k)
			t[model.LabelName(labelName)] = model.LabelValue(v)
		}
		tg.Targets = append(tg.Targets, t)
	}

	return tg
}

func parseServersetMember(data []byte, path string) (model.LabelSet, error) {
	member := serversetMember{}

	if err := json.Unmarshal(data, &member); err != nil {
		return nil, fmt.Errorf("error unmarshaling serverset member %q: %s", path, err)
	}

	labels := model.LabelSet{}
	labels[serversetPathLabel] = model.LabelValue(path)
	labels[model.AddressLabel] = model.LabelValue(
		net.JoinHostPort(member.ServiceEndpoint.Host, fmt.Sprintf("%d", member.ServiceEndpoint.Port)))

	labels[serversetEndpointLabelPrefix+"_host"] = model.LabelValue(member.ServiceEndpoint.Host)
	labels[serversetEndpointLabelPrefix+"_port"] = model.LabelValue(fmt.Sprintf("%d", member.ServiceEndpoint.Port))

	for name, endpoint := range member.AdditionalEndpoints {
		cleanName := model.LabelName(strutil.SanitizeLabelName(name))
		labels[serversetEndpointLabelPrefix+"_host_"+cleanName] = model.LabelValue(
			endpoint.Host)
		labels[serversetEndpointLabelPrefix+"_port_"+cleanName] = model.LabelValue(
			fmt.Sprintf("%d", endpoint.Port))

	}

	labels[serversetStatusLabel] = model.LabelValue(member.Status)
	labels[serversetShardLabel] = model.LabelValue(strconv.Itoa(member.Shard))

	return labels, nil
}

func nodeLabels(n *apiv1.Node) model.LabelSet {
	ls := make(model.LabelSet, len(n.Labels)+len(n.Annotations)+2)

	ls[nodeNameLabel] = lv(n.Name)

	for k, v := range n.Labels {
		ln := strutil.SanitizeLabelName(nodeLabelPrefix + k)
		ls[model.LabelName(ln)] = lv(v)
	}

	for k, v := range n.Annotations {
		ln := strutil.SanitizeLabelName(nodeAnnotationPrefix + k)
		ls[model.LabelName(ln)] = lv(v)
	}
	return ls
}

func (n *Node) buildNode(node *apiv1.Node) *config.TargetGroup {
	tg := &config.TargetGroup{
		Source: nodeSource(node),
	}
	tg.Labels = nodeLabels(node)

	addr, addrMap, err := nodeAddress(node)
	if err != nil {
		n.logger.With("err", err).Debugf("No node address found")
		return nil
	}
	addr = net.JoinHostPort(addr, strconv.FormatInt(int64(node.Status.DaemonEndpoints.KubeletEndpoint.Port), 10))

	t := model.LabelSet{
		model.AddressLabel:  lv(addr),
		model.InstanceLabel: lv(node.Name),
	}

	for ty, a := range addrMap {
		ln := strutil.SanitizeLabelName(nodeAddressPrefix + string(ty))
		t[model.LabelName(ln)] = lv(a[0])
	}
	tg.Targets = append(tg.Targets, t)

	return tg
}

func (ed *EC2Discovery) refresh() (*config.TargetGroup, error) {
	ec2s := ec2.New(ed.aws)
	tg := &config.TargetGroup{
		Source: *ed.aws.Region,
	}
	if err := ec2s.DescribeInstancesPages(nil, func(p *ec2.DescribeInstancesOutput, lastPage bool) bool {
		for _, r := range p.Reservations {
			for _, inst := range r.Instances {
				if inst.PrivateIpAddress == nil {
					continue
				}
				labels := model.LabelSet{
					ec2LabelInstanceID: model.LabelValue(*inst.InstanceId),
				}
				if inst.PublicIpAddress != nil {
					labels[ec2LabelPublicIP] = model.LabelValue(*inst.PublicIpAddress)
				}
				labels[ec2LabelPrivateIP] = model.LabelValue(*inst.PrivateIpAddress)
				addr := fmt.Sprintf("%s:%d", *inst.PrivateIpAddress, ed.port)
				labels[model.AddressLabel] = model.LabelValue(addr)
				for _, t := range inst.Tags {
					name := strutil.SanitizeLabelName(*t.Key)
					labels[ec2LabelTag+model.LabelName(name)] = model.LabelValue(*t.Value)
				}
				tg.Targets = append(tg.Targets, labels)
			}
		}
		return true
	}); err != nil {
		return nil, fmt.Errorf("could not describe instances: %s", err)
	}
	return tg, nil
}

func (kd *Discovery) updateNodesTargetGroup() *config.TargetGroup {
	kd.nodesMu.RLock()
	defer kd.nodesMu.RUnlock()

	tg := &config.TargetGroup{
		Source: nodesTargetGroupName,
		Labels: model.LabelSet{
			roleLabel: model.LabelValue("node"),
		},
	}

	// Now let's loop through the nodes & add them to the target group with appropriate labels.
	for nodeName, node := range kd.nodes {
		nodeAddress, err := nodeHostIP(node)
		if err != nil {
			log.Debugf("Skipping node %s: %s", node.Name, err)
			continue
		}

		address := fmt.Sprintf("%s:%d", nodeAddress.String(), kd.Conf.KubeletPort)

		t := model.LabelSet{
			model.AddressLabel:  model.LabelValue(address),
			model.InstanceLabel: model.LabelValue(nodeName),
		}
		for k, v := range node.ObjectMeta.Labels {
			labelName := strutil.SanitizeLabelName(nodeLabelPrefix + k)
			t[model.LabelName(labelName)] = model.LabelValue(v)
		}
		tg.Targets = append(tg.Targets, t)
	}

	return tg
}

func serviceLabels(svc *apiv1.Service) model.LabelSet {
	ls := make(model.LabelSet, len(svc.Labels)+len(svc.Annotations)+2)

	ls[serviceNameLabel] = lv(svc.Name)

	for k, v := range svc.Labels {
		ln := strutil.SanitizeLabelName(serviceLabelPrefix + k)
		ls[model.LabelName(ln)] = lv(v)
	}

	for k, v := range svc.Annotations {
		ln := strutil.SanitizeLabelName(serviceAnnotationPrefix + k)
		ls[model.LabelName(ln)] = lv(v)
	}
	return ls
}

func (kd *Discovery) updateNodesTargetGroup() *config.TargetGroup {
	kd.nodesMu.RLock()
	defer kd.nodesMu.RUnlock()

	tg := &config.TargetGroup{
		Source: nodesTargetGroupName,
		Labels: model.LabelSet{
			roleLabel: model.LabelValue("node"),
		},
	}

	// Now let's loop through the nodes & add them to the target group with appropriate labels.
	for nodeName, node := range kd.nodes {
		defaultNodeAddress, nodeAddressMap, err := nodeAddresses(node)
		if err != nil {
			log.Debugf("Skipping node %s: %s", node.Name, err)
			continue
		}

		kubeletPort := int(node.Status.DaemonEndpoints.KubeletEndpoint.Port)

		address := fmt.Sprintf("%s:%d", defaultNodeAddress.String(), kubeletPort)

		t := model.LabelSet{
			model.AddressLabel:  model.LabelValue(address),
			model.InstanceLabel: model.LabelValue(nodeName),
		}

		for addrType, ip := range nodeAddressMap {
			labelName := strutil.SanitizeLabelName(nodeAddressPrefix + string(addrType))
			t[model.LabelName(labelName)] = model.LabelValue(ip[0].String())
		}

		t[model.LabelName(nodePortLabel)] = model.LabelValue(strconv.Itoa(kubeletPort))

		for k, v := range node.ObjectMeta.Labels {
			labelName := strutil.SanitizeLabelName(nodeLabelPrefix + k)
			t[model.LabelName(labelName)] = model.LabelValue(v)
		}
		tg.Targets = append(tg.Targets, t)
	}

	return tg
}

func (ed *EC2Discovery) refresh() (*config.TargetGroup, error) {
	ec2s := ec2.New(ed.aws)
	tg := &config.TargetGroup{
		Source: *ed.aws.Region,
	}
	if err := ec2s.DescribeInstancesPages(nil, func(p *ec2.DescribeInstancesOutput, lastPage bool) bool {
		for _, r := range p.Reservations {
			for _, inst := range r.Instances {
				if inst.PrivateIpAddress == nil {
					continue
				}
				labels := model.LabelSet{
					ec2LabelInstanceID: model.LabelValue(*inst.InstanceId),
				}
				labels[ec2LabelPrivateIP] = model.LabelValue(*inst.PrivateIpAddress)
				addr := net.JoinHostPort(*inst.PrivateIpAddress, fmt.Sprintf("%d", ed.port))
				labels[model.AddressLabel] = model.LabelValue(addr)

				if inst.PublicIpAddress != nil {
					labels[ec2LabelPublicIP] = model.LabelValue(*inst.PublicIpAddress)
					labels[ec2LabelPublicDNS] = model.LabelValue(*inst.PublicDnsName)
				}

				labels[ec2LabelAZ] = model.LabelValue(*inst.Placement.AvailabilityZone)
				labels[ec2LabelInstanceState] = model.LabelValue(*inst.State.Name)

				if inst.VpcId != nil {
					labels[ec2LabelVPCID] = model.LabelValue(*inst.VpcId)

					subnetsMap := make(map[string]struct{})
					for _, eni := range inst.NetworkInterfaces {
						subnetsMap[*eni.SubnetId] = struct{}{}
					}
					subnets := []string{}
					for k := range subnetsMap {
						subnets = append(subnets, k)
					}
					labels[ec2LabelSubnetID] = model.LabelValue(
						subnetSeparator +
							strings.Join(subnets, subnetSeparator) +
							subnetSeparator)
				}

				for _, t := range inst.Tags {
					name := strutil.SanitizeLabelName(*t.Key)
					labels[ec2LabelTag+model.LabelName(name)] = model.LabelValue(*t.Value)
				}
				tg.Targets = append(tg.Targets, labels)
			}
		}
		return true
	}); err != nil {
		return nil, fmt.Errorf("could not describe instances: %s", err)
	}
	return tg, nil
}

func podLabels(pod *apiv1.Pod) model.LabelSet {
	ls := model.LabelSet{
		podNameLabel:     lv(pod.ObjectMeta.Name),
		podIPLabel:       lv(pod.Status.PodIP),
		podReadyLabel:    podReady(pod),
		podNodeNameLabel: lv(pod.Spec.NodeName),
		podHostIPLabel:   lv(pod.Status.HostIP),
	}

	for k, v := range pod.Labels {
		ln := strutil.SanitizeLabelName(podLabelPrefix + k)
		ls[model.LabelName(ln)] = lv(v)
	}

	for k, v := range pod.Annotations {
		ln := strutil.SanitizeLabelName(podAnnotationPrefix + k)
		ls[model.LabelName(ln)] = lv(v)
	}

	return ls
}

func (kd *KubernetesDiscovery) updateServiceTargetGroup(service *Service, endpoints *Endpoints) *config.TargetGroup {
	tg := &config.TargetGroup{
		Source: serviceSource(service),
		Labels: clientmodel.LabelSet{
			serviceNamespaceLabel: clientmodel.LabelValue(service.ObjectMeta.Namespace),
			serviceNameLabel:      clientmodel.LabelValue(service.ObjectMeta.Name),
		},
	}

	for k, v := range service.ObjectMeta.Labels {
		labelName := strutil.SanitizeLabelName(serviceLabelPrefix + k)
		tg.Labels[clientmodel.LabelName(labelName)] = clientmodel.LabelValue(v)
	}

	for k, v := range service.ObjectMeta.Annotations {
		labelName := strutil.SanitizeLabelName(serviceAnnotationPrefix + k)
		tg.Labels[clientmodel.LabelName(labelName)] = clientmodel.LabelValue(v)
	}

	// Now let's loop through the endpoints & add them to the target group with appropriate labels.
	for _, eps := range endpoints.Subsets {
		epPort := eps.Ports[0].Port

		for _, addr := range eps.Addresses {
			ipAddr := addr.IP
			if len(ipAddr) == net.IPv6len {
				ipAddr = "[" + ipAddr + "]"
			}
			address := fmt.Sprintf("%s:%d", ipAddr, epPort)

			t := clientmodel.LabelSet{clientmodel.AddressLabel: clientmodel.LabelValue(address)}

			tg.Targets = append(tg.Targets, t)
		}
	}

	return tg
}

func updatePodTargets(pod *Pod, allContainers bool) []model.LabelSet {
	var targets []model.LabelSet = make([]model.LabelSet, 0, len(pod.PodSpec.Containers))
	if pod.PodStatus.PodIP == "" {
		log.Debugf("skipping pod %s -- PodStatus.PodIP is empty", pod.ObjectMeta.Name)
		return targets
	}

	if pod.PodStatus.Phase != "Running" {
		log.Debugf("skipping pod %s -- status is not `Running`", pod.ObjectMeta.Name)
		return targets
	}

	ready := "unknown"
	for _, cond := range pod.PodStatus.Conditions {
		if strings.ToLower(cond.Type) == "ready" {
			ready = strings.ToLower(cond.Status)
		}
	}

	sort.Sort(ByContainerName(pod.PodSpec.Containers))

	for _, container := range pod.PodSpec.Containers {
		// Collect a list of TCP ports
		// Sort by port number, ascending
		// Product a target pointed at the first port
		// Include a label containing all ports (portName=port,PortName=port,...,)
		var tcpPorts []ContainerPort
		var portLabel *bytes.Buffer = bytes.NewBufferString(",")

		for _, port := range container.Ports {
			if port.Protocol == "TCP" {
				tcpPorts = append(tcpPorts, port)
			}
		}

		if len(tcpPorts) == 0 {
			log.Debugf("skipping container %s with no TCP ports", container.Name)
			continue
		}

		sort.Sort(ByContainerPort(tcpPorts))

		t := model.LabelSet{
			model.AddressLabel:        model.LabelValue(net.JoinHostPort(pod.PodIP, strconv.FormatInt(int64(tcpPorts[0].ContainerPort), 10))),
			podNameLabel:              model.LabelValue(pod.ObjectMeta.Name),
			podAddressLabel:           model.LabelValue(pod.PodStatus.PodIP),
			podNamespaceLabel:         model.LabelValue(pod.ObjectMeta.Namespace),
			podContainerNameLabel:     model.LabelValue(container.Name),
			podContainerPortNameLabel: model.LabelValue(tcpPorts[0].Name),
			podReadyLabel:             model.LabelValue(ready),
		}

		for _, port := range tcpPorts {
			portLabel.WriteString(port.Name)
			portLabel.WriteString("=")
			portLabel.WriteString(strconv.FormatInt(int64(port.ContainerPort), 10))
			portLabel.WriteString(",")
			t[model.LabelName(podContainerPortMapPrefix+port.Name)] = model.LabelValue(strconv.FormatInt(int64(port.ContainerPort), 10))
		}

		t[model.LabelName(podContainerPortListLabel)] = model.LabelValue(portLabel.String())

		for k, v := range pod.ObjectMeta.Labels {
			labelName := strutil.SanitizeLabelName(podLabelPrefix + k)
			t[model.LabelName(labelName)] = model.LabelValue(v)
		}

		for k, v := range pod.ObjectMeta.Annotations {
			labelName := strutil.SanitizeLabelName(podAnnotationPrefix + k)
			t[model.LabelName(labelName)] = model.LabelValue(v)
		}

		targets = append(targets, t)

		if !allContainers {
			break
		}
	}

	if len(targets) == 0 {
		log.Debugf("no targets for pod %s", pod.ObjectMeta.Name)
	}

	return targets
}

func (ad *AzureDiscovery) refresh() (tg *config.TargetGroup, err error) {
	t0 := time.Now()
	defer func() {
		azureSDRefreshDuration.Observe(time.Since(t0).Seconds())
		if err != nil {
			azureSDRefreshFailuresCount.Inc()
		}
	}()
	tg = &config.TargetGroup{}
	client, err := createAzureClient(*ad.cfg)
	if err != nil {
		return tg, fmt.Errorf("could not create Azure client: %s", err)
	}

	var machines []compute.VirtualMachine
	result, err := client.vm.ListAll()
	if err != nil {
		return tg, fmt.Errorf("could not list virtual machines: %s", err)
	}
	machines = append(machines, *result.Value...)

	// If we still have results, keep going until we have no more.
	for result.NextLink != nil {
		result, err = client.vm.ListAllNextResults(result)
		if err != nil {
			return tg, fmt.Errorf("could not list virtual machines: %s", err)
		}
		machines = append(machines, *result.Value...)
	}
	log.Debugf("Found %d virtual machines during Azure discovery.", len(machines))

	// We have the slice of machines. Now turn them into targets.
	// Doing them in go routines because the network interface calls are slow.
	type target struct {
		labelSet model.LabelSet
		err      error
	}

	ch := make(chan target, len(machines))
	for i, vm := range machines {
		go func(i int, vm compute.VirtualMachine) {
			r, err := newAzureResourceFromID(*vm.ID)
			if err != nil {
				ch <- target{labelSet: nil, err: err}
				return
			}

			labels := model.LabelSet{
				azureLabelMachineID:            model.LabelValue(*vm.ID),
				azureLabelMachineName:          model.LabelValue(*vm.Name),
				azureLabelMachineLocation:      model.LabelValue(*vm.Location),
				azureLabelMachineResourceGroup: model.LabelValue(r.ResourceGroup),
			}

			if vm.Tags != nil {
				for k, v := range *vm.Tags {
					name := strutil.SanitizeLabelName(k)
					labels[azureLabelMachineTag+model.LabelName(name)] = model.LabelValue(*v)
				}
			}

			// Get the IP address information via separate call to the network provider.
			for _, nic := range *vm.Properties.NetworkProfile.NetworkInterfaces {
				r, err := newAzureResourceFromID(*nic.ID)
				if err != nil {
					ch <- target{labelSet: nil, err: err}
					return
				}
				networkInterface, err := client.nic.Get(r.ResourceGroup, r.Name, "")
				if err != nil {
					log.Errorf("Unable to get network interface %s: %s", r.Name, err)
					ch <- target{labelSet: nil, err: err}
					// Get out of this routine because we cannot continue without a network interface.
					return
				}

				// Unfortunately Azure does not return information on whether a VM is deallocated.
				// This information is available via another API call however the Go SDK does not
				// yet support this. On deallocated machines, this value happens to be nil so it
				// is a cheap and easy way to determine if a machine is allocated or not.
				if networkInterface.Properties.Primary == nil {
					log.Debugf("Virtual machine %s is deallocated. Skipping during Azure SD.", *vm.Name)
					ch <- target{}
					return
				}

				if *networkInterface.Properties.Primary {
					for _, ip := range *networkInterface.Properties.IPConfigurations {
						if ip.Properties.PrivateIPAddress != nil {
							labels[azureLabelMachinePrivateIP] = model.LabelValue(*ip.Properties.PrivateIPAddress)
							address := net.JoinHostPort(*ip.Properties.PrivateIPAddress, fmt.Sprintf("%d", ad.port))
							labels[model.AddressLabel] = model.LabelValue(address)
							ch <- target{labelSet: labels, err: nil}
							return
						}
						// If we made it here, we don't have a private IP which should be impossible.
						// Return an empty target and error to ensure an all or nothing situation.
						err = fmt.Errorf("unable to find a private IP for VM %s", *vm.Name)
						ch <- target{labelSet: nil, err: err}
						return
//.........这里部分代码省略.........

func (gd *GCEDiscovery) refresh() (tg *config.TargetGroup, err error) {
	t0 := time.Now()
	defer func() {
		gceSDRefreshDuration.Observe(time.Since(t0).Seconds())
		if err != nil {
			gceSDRefreshFailuresCount.Inc()
		}
	}()

	tg = &config.TargetGroup{
		Source: fmt.Sprintf("GCE_%s_%s", gd.project, gd.zone),
	}

	ilc := gd.isvc.List(gd.project, gd.zone)
	if len(gd.filter) > 0 {
		ilc = ilc.Filter(gd.filter)
	}
	err = ilc.Pages(nil, func(l *compute.InstanceList) error {
		for _, inst := range l.Items {
			if len(inst.NetworkInterfaces) == 0 {
				continue
			}
			labels := model.LabelSet{
				gceLabelProject:        model.LabelValue(gd.project),
				gceLabelZone:           model.LabelValue(inst.Zone),
				gceLabelInstanceName:   model.LabelValue(inst.Name),
				gceLabelInstanceStatus: model.LabelValue(inst.Status),
			}
			priIface := inst.NetworkInterfaces[0]
			labels[gceLabelNetwork] = model.LabelValue(priIface.Network)
			labels[gceLabelSubnetwork] = model.LabelValue(priIface.Subnetwork)
			labels[gceLabelPrivateIP] = model.LabelValue(priIface.NetworkIP)
			addr := fmt.Sprintf("%s:%d", priIface.NetworkIP, gd.port)
			labels[model.AddressLabel] = model.LabelValue(addr)

			// Tags in GCE are usually only used for networking rules.
			if inst.Tags != nil && len(inst.Tags.Items) > 0 {
				// We surround the separated list with the separator as well. This way regular expressions
				// in relabeling rules don't have to consider tag positions.
				tags := gd.tagSeparator + strings.Join(inst.Tags.Items, gd.tagSeparator) + gd.tagSeparator
				labels[gceLabelTags] = model.LabelValue(tags)
			}

			// GCE metadata are key-value pairs for user supplied attributes.
			if inst.Metadata != nil {
				for _, i := range inst.Metadata.Items {
					// Protect against occasional nil pointers.
					if i.Value == nil {
						continue
					}
					name := strutil.SanitizeLabelName(i.Key)
					labels[gceLabelMetadata+model.LabelName(name)] = model.LabelValue(*i.Value)
				}
			}

			if len(priIface.AccessConfigs) > 0 {
				ac := priIface.AccessConfigs[0]
				if ac.Type == "ONE_TO_ONE_NAT" {
					labels[gceLabelPublicIP] = model.LabelValue(ac.NatIP)
				}
			}
			tg.Targets = append(tg.Targets, labels)
		}
		return nil
	})
	if err != nil {
		return tg, fmt.Errorf("error retrieving refresh targets from gce: %s", err)
	}
	return tg, nil
}