Allow custom-sized CIDR for the management subnets

The octavia-operator previously required the user to pass /16 (or /64
for IPv6) CIDRs for the management subnets, now it's more flexible and
allows custom sized CIDRs
The functional tests now check that the allocation pools are correctly
set, based on those CIDRs.

JIRA: OSPRH-11711

Author: gthiemonge

pkg/octavia/network_parameters.go

@@ -55,33 +55,31 @@ func getConfigFromNAD(
 func GetRangeFromCIDR(
 	cidr netip.Prefix,
 ) (start netip.Addr, end netip.Addr) {
-	// For IPv6, a /64 is expected, if the CIDR is aaaa:bbbb:cccc:dddd::/64,
-	// the range is aaaa:bbbb:cccc:dddd::5 - aaaa:bbbb:cccc:dddd:ffff:ffff:ffff:fffe
-	// For IPv4, a /16 is expected, if the CIDR is a.b.0.0/16
-	// the range is a.b.0.5 - a.b.255.254
-	// IPs from from 1 to 5 are reserved for later user
-	addr := cidr.Addr()
-	if addr.Is6() {
-		addrBytes := addr.As16()
-		for i := 8; i < 15; i++ {
-			addrBytes[i] = 0
-		}
-		addrBytes[15] = 5
-		start = netip.AddrFrom16(addrBytes)
-		for i := 8; i < 15; i++ {
-			addrBytes[i] = 0xff
-		}
-		addrBytes[15] = 0xfe
-		end = netip.AddrFrom16(addrBytes)
-	} else {
-		addrBytes := addr.As4()
-		addrBytes[2] = 0
-		addrBytes[3] = 5
-		start = netip.AddrFrom4(addrBytes)
-		addrBytes[2] = 0xff
-		addrBytes[3] = 0xfe
-		end = netip.AddrFrom4(addrBytes)
+	// start is the 5th address of the Cidr
+	start = cidr.Masked().Addr()
+	for i := 0; i < 5; i++ {
+		start = start.Next()
+	}
+
+	bits := cidr.Bits()
+	if start.Is4() {
+		// Padding for ipv4 addresses in a [16]bytes table
+		bits += 96
+	}
+	// convert it to a [16]bytes table, set the remaining bits to 1
+	addrBytes := start.As16()
+	for b := bits; b < 128; b++ {
+		addrBytes[b/8] |= 1 << uint(7-(b%8))
 	}
+	// convert the table to an ip address to get the last IP
+	// in case of IPv4, the address should be unmapped
+	last := netip.AddrFrom16(addrBytes)
+	if start.Is4() {
+		last = last.Unmap()
+	}
+	// end is the 2nd last
+	end = last.Prev()
+
 	return
 }
 

tests/functional/octavia_controller_test.go

@@ -663,7 +663,7 @@ var _ = Describe("Octavia controller", func() {
 
 			spec["lbMgmtNetwork"].(map[string]interface{})["availabilityZoneCIDRs"] = map[string]string{
 				"az1": "172.34.0.0/16",
-				"az2": "172.44.0.0/16",
+				"az2": "172.44.8.0/21",
 			}
 			spec["lbMgmtNetwork"].(map[string]interface{})["createDefaultLbMgmtNetwork"] = false
 			DeferCleanup(th.DeleteInstance, CreateOctavia(octaviaName, spec))
@@ -763,6 +763,16 @@ var _ = Describe("Octavia controller", func() {
 					CIDR:        nadConfig.IPAM.CIDR.String(),
 				},
 			}
+			expectedAllocationPools := map[string]subnets.AllocationPool{
+				subnetNameAZ1: {
+					Start: "172.34.0.5",
+					End:   "172.34.255.254",
+				},
+				subnetNameAZ2: {
+					Start: "172.44.8.5",
+					End:   "172.44.15.254",
+				},
+			}
 
 			resultSubnets := map[string]subnets.Subnet{}
 			for _, subnet := range apiFixtures.Neutron.Subnets {
@@ -777,6 +787,10 @@ var _ = Describe("Octavia controller", func() {
 				Expect(subnet.NetworkID).To(Equal(expectedSubnet.NetworkID))
 				Expect(subnet.CIDR).To(Equal(expectedSubnet.CIDR))
 				Expect(subnet.HostRoutes).To(Equal(expectedSubnet.HostRoutes))
+				if expectedAllocationPool, ok := expectedAllocationPools[name]; ok {
+					Expect(subnet.AllocationPools[0].Start).To(Equal(expectedAllocationPool.Start))
+					Expect(subnet.AllocationPools[0].End).To(Equal(expectedAllocationPool.End))
+				}
 			}
 
 			// Routers