synthesise k8s service network from service IPs

This prevents cluttering host.LocalNetworks with lots of /32
addresses. These were unsightly and rather distracting in the UI. They
also bloated the report and slowed down server-side rendering.

Fixes #2748.

probe/kubernetes/reporter.go

@@ -2,6 +2,7 @@ package kubernetes
 
 import (
 	"fmt"
+	"net"
 	"strings"
 
 	"k8s.io/apimachinery/pkg/labels"
@@ -294,23 +295,32 @@ func (r *Reporter) serviceTopology() (report.Topology, []Service, error) {
 	return result, services, err
 }
 
-// FIXME: Hideous hack to remove persistent-connection edges to virtual service
-//        IPs attributed to the internet. We add each service IP as a /32 network
-//        (the global service-cluster-ip-range is not exposed by the API
-//        server so we treat each IP as a /32 network see
-//        https://github.com/kubernetes/kubernetes/issues/25533).
-//        The right way of fixing this is performing DNAT mapping on persistent
-//        connections for which we don't have a robust solution
-//        (see https://github.com/weaveworks/scope/issues/1491)
+// FIXME: Hideous hack to remove persistent-connection edges to
+// virtual service IPs attributed to the internet. The global
+// service-cluster-ip-range is not exposed by the API server (see
+// https://github.com/kubernetes/kubernetes/issues/25533), so instead
+// we synthesise it by computing the smallest network that contains
+// all service IPs. That network may be smaller than the actual range
+// but that is ok, since in the end all we care about is that it
+// contains all the service IPs.
+//
+// The right way of fixing this is performing DNAT mapping on
+// persistent connections for which we don't have a robust solution
+// (see https://github.com/weaveworks/scope/issues/1491).
 func (r *Reporter) hostTopology(services []Service) report.Topology {
-	localNetworks := report.MakeStringSet()
+	serviceIPs := make([]net.IP, 0, len(services))
 	for _, service := range services {
-		localNetworks = localNetworks.Add(service.ClusterIP() + "/32")
+		if ip := net.ParseIP(service.ClusterIP()).To4(); ip != nil {
+			serviceIPs = append(serviceIPs, ip)
+		}
 	}
-	node := report.MakeNode(report.MakeHostNodeID(r.hostID))
-	node = node.WithSets(report.MakeSets().
-		Add(host.LocalNetworks, localNetworks))
-	return report.MakeTopology().AddNode(node)
+	serviceNetwork := report.ContainingIPv4Network(serviceIPs)
+	if serviceNetwork == nil {
+		return report.MakeTopology()
+	}
+	return report.MakeTopology().AddNode(
+		report.MakeNode(report.MakeHostNodeID(r.hostID)).
+			WithSets(report.MakeSets().Add(host.LocalNetworks, report.MakeStringSet(serviceNetwork.String()))))
 }
 
 func (r *Reporter) deploymentTopology(probeID string) (report.Topology, []Deployment, error) {

report/networks.go

@@ -1,6 +1,7 @@
 package report
 
 import (
+	"encoding/binary"
 	"net"
 	"strings"
 
@@ -105,3 +106,32 @@ func ipv4Nets(addrs []net.Addr) []*net.IPNet {
 	}
 	return nets
 }
+
+// ContainingIPv4Network determines the smallest network containing
+// the given IPv4 addresses. When no addresses are specified, nil is
+// returned.
+func ContainingIPv4Network(ips []net.IP) *net.IPNet {
+	if len(ips) == 0 {
+		return nil
+	}
+	network := net.IPNet{
+		IP:   ips[0],
+		Mask: net.CIDRMask(net.IPv4len*8, net.IPv4len*8),
+	}
+	for _, ip := range ips[1:] {
+		network.Mask = net.CIDRMask(commonIPv4PrefixLen(network.IP, ip), net.IPv4len*8)
+		network.IP = network.IP.Mask(network.Mask)
+	}
+	return &network
+}
+
+func commonIPv4PrefixLen(a, b net.IP) int {
+	x := binary.BigEndian.Uint32(a)
+	y := binary.BigEndian.Uint32(b)
+	cpl := 32
+	for ; x != y; cpl-- {
+		x >>= 1
+		y >>= 1
+	}
+	return cpl
+}

report/networks_test.go

@@ -4,6 +4,7 @@ import (
 	"net"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/weaveworks/scope/report"
 )
 
@@ -23,3 +24,18 @@ func TestContains(t *testing.T) {
 		t.Errorf("10.0.0.1 in %v", networks)
 	}
 }
+
+func TestContainingIPv4Network(t *testing.T) {
+	assert.Nil(t, containingIPv4Networks([]string{}))
+	assert.Equal(t, "10.0.0.1/32", containingIPv4Networks([]string{"10.0.0.1"}).String())
+	assert.Equal(t, "10.0.0.0/17", containingIPv4Networks([]string{"10.0.0.1", "10.0.2.55", "10.0.106.48"}).String())
+	assert.Equal(t, "0.0.0.0/0", containingIPv4Networks([]string{"10.0.0.1", "192.168.0.1"}).String())
+}
+
+func containingIPv4Networks(ipstrings []string) *net.IPNet {
+	ips := make([]net.IP, len(ipstrings))
+	for i, ip := range ipstrings {
+		ips[i] = net.ParseIP(ip).To4()
+	}
+	return report.ContainingIPv4Network(ips)
+}