rings: RingThreePrefix()

Ring 3 corresponds to the pods of the kubernetes cluster of a region

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/rings/rings.go

@@ -24,6 +24,9 @@ const (
 	RingZeroBits = 16
 	// RingOneBits indicates the size of the prefix on the ring 1 (lan) network.
 	RingOneBits = 20
+	// RingThreeBits indicates the size of the prefix on the ring 3 (pods) network
+	// of the kubernetes cluster of a region.
+	RingThreeBits = 12
 )
 
 // RegionID is the identifier of a region, valid between 1 and [RegionMax].
@@ -128,6 +131,21 @@ func RingOneAddress(region RegionID, zone ZoneID, node NodeID) (addr netip.Addr,
 	return addr, err
 }
 
+// RingThreePrefix returns the subnet corresponding to
+// the pods of a cluster.
+//
+// Ring 3 is a `10.(region_id << 4).0.0/12` network
+func RingThreePrefix(region RegionID) (subnet netip.Prefix, err error) {
+	switch {
+	case !region.Valid():
+		err = ErrOutOfRange(region, "region")
+	default:
+		addr := unsafeRingThreeAddress(region, 0)
+		subnet = netip.PrefixFrom(addr, RingThreeBits)
+	}
+	return subnet, err
+}
+
 func unsafeRingZeroAddress(region RegionID, zone ZoneID, node NodeID) netip.Addr {
 	r := uint(region)
 	z := uint(zone)
@@ -146,3 +164,13 @@ func unsafeRingOneAddress(region RegionID, zone ZoneID, node NodeID) netip.Addr
 
 	return AddrFrom4(10, r, z<<4+n1, n0)
 }
+
+func unsafeRingThreeAddress(region RegionID, n uint) netip.Addr {
+	r := uint(region)
+
+	n2 := n >> 16
+	n1 := n >> 8
+	n0 := n >> 0
+
+	return AddrFrom4(10, r<<4+n2, n1, n0)
+}