cmd/microcloud: detect local net interface collisions within a member…

… and global subnet collisions in a cluster of members

* If a member have multiple network types going through the same interface, show a warning.
* If multiple subnet types are detected to use the same subnet at a cluster level, show a warning.

Signed-off-by: Gabriel Mougard <gabriel.mougard@canonical.com>

cmd/microcloud/main_init.go

@@ -515,15 +515,81 @@ func validateGatewayNet(config map[string]string, ipPrefix string, cidrValidator
 }
 
 func (c *initConfig) validateSystems(s *service.Handler) (err error) {
-	for _, sys := range c.systems {
+	// subnetsCollisionMap maps a subnet CIDR notation to a map of subnet type to peer names.
+	//
+	// Example:
+	// {
+	//   "10.0.1.0/24": {
+	//       "OVN underlay": ["system1", "system2"],
+	//       "Ceph cluster network": ["system3"]
+	//    },
+	//   "10.0.2.0/24": {
+	//        "Ceph public network": ["system1", "system2", "system3"],
+	//    }
+	// }
+	//
+	// In this example, we have a collision for the subnet "10.0.1.0/24":
+	//  - system1 and system2 are using it for the OVN underlay, whereas system3 is using it for the Ceph cluster network.
+	// Everything is fine for the subnet "10.0.2.0/24" as all systems are using it for the Ceph public network.
+	subnetsCollisionMap := make(map[string]map[string][]string)
+	for peer, sys := range c.systems {
 		if sys.MicroCephInternalNetwork == nil || sys.OVNGeneveNetwork == nil {
 			continue
 		}
 
-		if sys.MicroCephInternalNetwork.Subnet.Contains(sys.OVNGeneveNetwork.IP) {
-			fmt.Printf("Warning: OVN underlay IP (%s) is shared with the Ceph cluster network (%s)\n", sys.OVNGeneveNetwork.IP.String(), sys.MicroCephInternalNetwork.Subnet.String())
+		// We also check for interface collisions at a local level.
+		// This means that we check if the same interface is used for multiple networks in a member.
+		netTypeToNet := map[string]*Network{
+			"Ceph cluster network": sys.MicroCephInternalNetwork,
+			"OVN underlay":         sys.OVNGeneveNetwork,
+		}
 
-			break
+		// The public Ceph network is not always present (partially disaggregated setup) but we still
+		// wish to check for interface collisions between OVN and the Ceph cluster network.
+		// If it is present though, add it to the list of interfaces to check for collisions.
+		if sys.MicroCephPublicNetwork != nil {
+			netTypeToNet["Ceph public network"] = sys.MicroCephPublicNetwork
+		}
+
+		// This is checking the local collisions (whether the same interface is used for multiple networks in a member).
+		for typeLeft, netLeft := range netTypeToNet {
+			for typeRight, netRight := range netTypeToNet {
+				// Skip self-comparison and already processed pairs
+				// (e.g. if we already compared "A vs B", we don't need to compare "B vs A").
+				if typeLeft >= typeRight {
+					continue
+				}
+
+				if netLeft.Interface == netRight.Interface {
+					fmt.Printf("Warning: %s is shared on the same network interface %q with the %s\n", typeLeft, netLeft.Interface, typeRight)
+				}
+
+				// Populate the subnetsCollisionMap with the subnet type and the peer using it.
+				subnetTypeToPeers, ok := subnetsCollisionMap[netLeft.Subnet.String()]
+				if !ok {
+					subnetTypeToPeers = make(map[string][]string)
+					subnetTypeToPeers[typeLeft] = make([]string, 0)
+					subnetTypeToPeers[typeLeft] = append(subnetTypeToPeers[typeLeft], peer)
+					subnetsCollisionMap[netLeft.Subnet.String()] = subnetTypeToPeers
+				} else {
+					subnetTypeToPeers[typeLeft] = append(subnetTypeToPeers[typeLeft], peer)
+				}
+			}
+		}
+	}
+
+	// Check for subnet collisions at the cluster level.
+	for subnet, subnetTypeToPeers := range subnetsCollisionMap {
+		// If there are multiple subnet types on the same subnet, we have a collision.
+		if len(subnetTypeToPeers) > 1 {
+			var sb strings.Builder
+			sb.WriteString("WARNING: Subnet collision detected:\n")
+			for subnetType, peers := range subnetTypeToPeers {
+				sb.WriteString(fmt.Sprintf("- Members %s are using the %q subnet for %s\n", strings.Join(peers, ", "), subnet, subnetType))
+			}
+
+			sb.WriteString("Please ensure that each subnet is used for a single network type.")
+			fmt.Printf("%s\n", sb.String())
 		}
 	}