constellation-node-operator: don't bail out on listing errors

If the GCP project has scaling groups for which our checks can't be performed (which is the case for regional scaling groups, as they "don't exist" for the operator, if deployed in another region) . In that case, we should not bail out directly but go on with the next group. An error should only be thrown if there are no matching groups at all.

operators/constellation-node-operator/internal/cloud/gcp/client/scalinggroup.go

@@ -103,8 +103,7 @@ func (c *Client) GetAutoscalingGroupName(scalingGroupID string) (string, error)
 }
 
 // ListScalingGroups retrieves a list of scaling groups for the cluster.
-func (c *Client) ListScalingGroups(ctx context.Context, uid string) ([]cspapi.ScalingGroup, error) {
-	results := []cspapi.ScalingGroup{}
+func (c *Client) ListScalingGroups(ctx context.Context, uid string) (results []cspapi.ScalingGroup, retErr error) {
 	iter := c.instanceGroupManagersAPI.AggregatedList(ctx, &computepb.AggregatedListInstanceGroupManagersRequest{
 		Project: c.projectID,
 	})
@@ -129,7 +128,7 @@ func (c *Client) ListScalingGroups(ctx context.Context, uid string) ([]cspapi.Sc
 			}
 			template, err := c.instanceTemplateAPI.Get(c.projectID, templateURI[len(templateURI)-1])
 			if err != nil {
-				return nil, fmt.Errorf("getting instance template: %w", err)
+				errors.Join(retErr, fmt.Errorf("getting instance template %q: %w", templateURI[len(templateURI)-1], err))
 			}
 			if template.Properties == nil || template.Properties.Labels == nil {
 				continue
@@ -140,14 +139,14 @@ func (c *Client) ListScalingGroups(ctx context.Context, uid string) ([]cspapi.Sc
 
 			groupID, err := c.canonicalInstanceGroupID(ctx, *grpManager.SelfLink)
 			if err != nil {
-				return nil, fmt.Errorf("normalizing instance group ID: %w", err)
+				errors.Join(retErr, fmt.Errorf("getting canonical instance group ID: %w", err))
 			}
 
 			role := updatev1alpha1.NodeRoleFromString(template.Properties.Labels["constellation-role"])
 
 			name, err := c.GetScalingGroupName(groupID)
 			if err != nil {
-				return nil, fmt.Errorf("getting scaling group name: %w", err)
+				errors.Join(retErr, fmt.Errorf("getting scaling group name: %w", err))
 			}
 
 			nodeGroupName := template.Properties.Labels["constellation-node-group"]
@@ -164,7 +163,7 @@ func (c *Client) ListScalingGroups(ctx context.Context, uid string) ([]cspapi.Sc
 
 			autoscalerGroupName, err := c.GetAutoscalingGroupName(groupID)
 			if err != nil {
-				return nil, fmt.Errorf("getting autoscaling group name: %w", err)
+				errors.Join(retErr, fmt.Errorf("getting autoscaling group name: %w", err))
 			}
 
 			results = append(results, cspapi.ScalingGroup{
@@ -176,6 +175,11 @@ func (c *Client) ListScalingGroups(ctx context.Context, uid string) ([]cspapi.Sc
 			})
 		}
 	}
+
+	if len(results) == 0 {
+		return nil, fmt.Errorf("no scaling groups found: %w", retErr)
+	}
+
 	return results, nil
 }