fix: enforce at most one IP per private network (#248)

Author: Tomy2e

docs/loadbalancer-annotations.md

@@ -233,6 +233,8 @@ The possible formats are:
 
 This is the annotation to statically set the private IPs of the loadbalancer.
 It is possible to provide a single IPAM IP ID, or a comma delimited list of IPAM IP IDs.
+Each IPAM IP ID will automatically be assigned to the appropriate Private Network attachment.
+Please note that there can be at most one IP address (IPv4 or IPv6) per Private Network.
 Changing the IPs will result in the re-creation of the Private Network attachments.
 The possible formats are:
 - `<ip-id>`: will attach a single IP to the LB.

scaleway/loadbalancers.go

@@ -921,6 +921,10 @@ func (l *loadbalancers) attachPrivateNetworks(loadbalancer *scwlb.LB, service *v
 
 	// Reconcile: skip already-correct attachments, detach+reattach if IPs changed, attach if missing.
 	for pnID, pnStatus := range privateNetworkAttachments {
+		if len(pnStatus.desiredIPIDs) > 1 {
+			return fmt.Errorf("at most one IP can be set per private network, please choose one between %s", pnStatus.desiredIPIDs)
+		}
+
 		if pnStatus.attached {
 			if len(pnStatus.desiredIPIDs) == 0 || slices.Equal(slices.Sorted(slices.Values(pnStatus.attachedIPIDs)), slices.Sorted(slices.Values(pnStatus.desiredIPIDs))) {
 				continue

scaleway/loadbalancers_annotations.go

@@ -225,6 +225,8 @@ const (
 
 	// serviceAnnotationLoadBalancerPrivateIPIDs is the annotation to statically set the private IPs of the loadbalancer.
 	// It is possible to provide a single IPAM IP ID, or a comma delimited list of IPAM IP IDs.
+	// Each IPAM IP ID will automatically be assigned to the appropriate Private Network attachment.
+	// Please note that there can be at most one IP address (IPv4 or IPv6) per Private Network.
 	// Changing the IPs will result in the re-creation of the Private Network attachments.
 	// The possible formats are:
 	// "<ip-id>": will attach a single IP to the LB.