Refactor: Azure Discovery: extract function to generate labelSet

This should make it easier to test.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

discovery/azure/azure.go

@@ -374,10 +374,32 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 	for _, vm := range machines {
 		go func(vm virtualMachine) {
 			defer wg.Done()
+			labelSet, err := d.vmToLabelSet(ctx, client, vm)
+			ch <- target{labelSet: labelSet, err: err}
+		}(vm)
+	}
+
+	wg.Wait()
+	close(ch)
+
+	var tg targetgroup.Group
+	for tgt := range ch {
+		if tgt.err != nil {
+			d.metrics.failuresCount.Inc()
+			return nil, fmt.Errorf("unable to complete Azure service discovery: %w", tgt.err)
+		}
+		if tgt.labelSet != nil {
+			tg.Targets = append(tg.Targets, tgt.labelSet)
+		}
+	}
+
+	return []*targetgroup.Group{&tg}, nil
+}
+
+func (d *Discovery) vmToLabelSet(ctx context.Context, client azureClient, vm virtualMachine) (model.LabelSet, error) {
 	r, err := newAzureResourceFromID(vm.ID, d.logger)
 	if err != nil {
-				ch <- target{labelSet: nil, err: err}
-				return
+		return nil, err
 	}
 
 	labels := model.LabelSet{
@@ -413,16 +435,14 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 			} else {
 				networkInterface, err = client.getVMScaleSetVMNetworkInterfaceByID(ctx, nicID, vm.ScaleSet, vm.InstanceID)
 			}
-
 			if err != nil {
 				if errors.Is(err, errorNotFound) {
 					level.Warn(d.logger).Log("msg", "Network interface does not exist", "name", nicID, "err", err)
 				} else {
-							ch <- target{labelSet: nil, err: err}
+					return nil, err
 				}
-
 				// Get out of this routine because we cannot continue without a network interface.
-						return
+				return nil, nil
 			}
 
 			// Continue processing with the network interface
@@ -439,7 +459,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 		// is a cheap and easy way to determine if a machine is allocated or not.
 		if networkInterface.Properties.Primary == nil {
 			level.Debug(d.logger).Log("msg", "Skipping deallocated virtual machine", "machine", vm.Name)
-					return
+			return nil, nil
 		}
 
 		if *networkInterface.Properties.Primary {
@@ -453,35 +473,16 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 					labels[azureLabelMachinePrivateIP] = model.LabelValue(*ip.Properties.PrivateIPAddress)
 					address := net.JoinHostPort(*ip.Properties.PrivateIPAddress, fmt.Sprintf("%d", d.port))
 					labels[model.AddressLabel] = model.LabelValue(address)
-							ch <- target{labelSet: labels, err: nil}
-							return
+					return labels, nil
 				}
 				// 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
+				return nil, fmt.Errorf("unable to find a private IP for VM %s", vm.Name)
 			}
 		}
 	}
-		}(vm)
-	}
-
-	wg.Wait()
-	close(ch)
-
-	var tg targetgroup.Group
-	for tgt := range ch {
-		if tgt.err != nil {
-			d.metrics.failuresCount.Inc()
-			return nil, fmt.Errorf("unable to complete Azure service discovery: %w", tgt.err)
-		}
-		if tgt.labelSet != nil {
-			tg.Targets = append(tg.Targets, tgt.labelSet)
-		}
-	}
-
-	return []*targetgroup.Group{&tg}, nil
+	// TODO: Should we say something at this point?
+	return nil, nil
 }
 
 func (client *azureClient) getVMs(ctx context.Context, resourceGroup string) ([]virtualMachine, error) {