trigger handshakes when lighthouse reply arrives (#246)

Currently, we wait until the next timer tick to act on the lighthouse's
reply to our HostQuery. This means we can easily add hundreds of
milliseconds of unnecessary delay to the handshake. To fix this, we
can introduce a channel to trigger an outbound handshake without waiting
for the next timer tick.

A few samples of cold ping time between two hosts that require a
lighthouse lookup:

    before (v1.2.0):

    time=156 ms
    time=252 ms
    time=12.6 ms
    time=301 ms
    time=352 ms
    time=49.4 ms
    time=150 ms
    time=13.5 ms
    time=8.24 ms
    time=161 ms
    time=355 ms

    after:

    time=3.53 ms
    time=3.14 ms
    time=3.08 ms
    time=3.92 ms
    time=7.78 ms
    time=3.59 ms
    time=3.07 ms
    time=3.22 ms
    time=3.12 ms
    time=3.08 ms
    time=8.04 ms

I recommend reviewing this PR by looking at each commit individually, as
some refactoring was required that makes the diff a bit confusing when
combined together.

examples/config.yml

@@ -194,6 +194,9 @@ logging:
   #retries: 20
   # wait_rotation is the number of handshake attempts to do before starting to try non-local IP addresses
   #wait_rotation: 5
+  # trigger_buffer is the size of the buffer channel for quickly sending handshakes
+  # after receiving the response for lighthouse queries
+  #trigger_buffer: 64
 
 # Nebula security group configuration
 firewall:

handshake_manager.go

@@ -17,6 +17,7 @@ const (
 	DefaultHandshakeRetries     = 20
 	// DefaultHandshakeWaitRotation is the number of handshake attempts to do before starting to use other ips addresses
 	DefaultHandshakeWaitRotation  = 5
+	DefaultHandshakeTriggerBuffer = 64
 )
 
 var (
@@ -24,6 +25,7 @@ var (
 		tryInterval:   DefaultHandshakeTryInterval,
 		retries:       DefaultHandshakeRetries,
 		waitRotation:  DefaultHandshakeWaitRotation,
+		triggerBuffer: DefaultHandshakeTriggerBuffer,
 	}
 )
 
@@ -31,6 +33,7 @@ type HandshakeConfig struct {
 	tryInterval   time.Duration
 	retries       int
 	waitRotation  int
+	triggerBuffer int
 
 	messageMetrics *MessageMetrics
 }
@@ -42,6 +45,9 @@ type HandshakeManager struct {
 	outside        *udpConn
 	config         HandshakeConfig
 
+	// can be used to trigger outbound handshake for the given vpnIP
+	trigger chan uint32
+
 	OutboundHandshakeTimer *SystemTimerWheel
 	InboundHandshakeTimer  *SystemTimerWheel
 
@@ -57,6 +63,8 @@ func NewHandshakeManager(tunCidr *net.IPNet, preferredRanges []*net.IPNet, mainH
 
 		config: config,
 
+		trigger: make(chan uint32, config.triggerBuffer),
+
 		OutboundHandshakeTimer: NewSystemTimerWheel(config.tryInterval, config.tryInterval*time.Duration(config.retries)),
 		InboundHandshakeTimer:  NewSystemTimerWheel(config.tryInterval, config.tryInterval*time.Duration(config.retries)),
 
@@ -66,11 +74,17 @@ func NewHandshakeManager(tunCidr *net.IPNet, preferredRanges []*net.IPNet, mainH
 
 func (c *HandshakeManager) Run(f EncWriter) {
 	clockSource := time.Tick(c.config.tryInterval)
-	for now := range clockSource {
+	for {
+		select {
+		case vpnIP := <-c.trigger:
+			l.WithField("vpnIp", IntIp(vpnIP)).Debug("HandshakeManager: triggered")
+			c.handleOutbound(vpnIP, f, true)
+		case now := <-clockSource:
 			c.NextOutboundHandshakeTimerTick(now, f)
 			c.NextInboundHandshakeTimerTick(now)
 		}
 	}
+}
 
 func (c *HandshakeManager) NextOutboundHandshakeTimerTick(now time.Time, f EncWriter) {
 	c.OutboundHandshakeTimer.advance(now)
@@ -80,15 +94,18 @@ func (c *HandshakeManager) NextOutboundHandshakeTimerTick(now time.Time, f EncWr
 			break
 		}
 		vpnIP := ep.(uint32)
-
+		c.handleOutbound(vpnIP, f, false)
-		index, err := c.pendingHostMap.GetIndexByVpnIP(vpnIP)
+	}
-		if err != nil {
-			continue
 }
 
+func (c *HandshakeManager) handleOutbound(vpnIP uint32, f EncWriter, lighthouseTriggered bool) {
+	index, err := c.pendingHostMap.GetIndexByVpnIP(vpnIP)
+	if err != nil {
+		return
+	}
 	hostinfo, err := c.pendingHostMap.QueryVpnIP(vpnIP)
 	if err != nil {
-			continue
+		return
 	}
 
 	// If we haven't finished the handshake and we haven't hit max retries, query
@@ -98,13 +115,26 @@ func (c *HandshakeManager) NextOutboundHandshakeTimerTick(now time.Time, f EncWr
 			// We continue to query the lighthouse because hosts may
 			// come online during handshake retries. If the query
 			// succeeds (no error), add the lighthouse info to hostinfo
-				ips, err := c.lightHouse.Query(vpnIP, f)
+			ips := c.lightHouse.QueryCache(vpnIP)
+			// If we have no responses yet, or only one IP (the host hadn't
+			// finished reporting its own IPs yet), then send another query to
+			// the LH.
+			if len(ips) <= 1 {
+				ips, err = c.lightHouse.Query(vpnIP, f)
+			}
 			if err == nil {
 				for _, ip := range ips {
 					hostinfo.AddRemote(ip)
 				}
 				hostinfo.ForcePromoteBest(c.mainHostMap.preferredRanges)
 			}
+		} else if lighthouseTriggered {
+			// We were triggered by a lighthouse HostQueryReply packet, but
+			// we have already picked a remote for this host (this can happen
+			// if we are configured with multiple lighthouses). So we can skip
+			// this trigger and let the timerwheel handle the rest of the
+			// process
+			return
 		}
 
 		hostinfo.HandshakeCounter++
@@ -137,14 +167,15 @@ func (c *HandshakeManager) NextOutboundHandshakeTimerTick(now time.Time, f EncWr
 		}
 
 		// Readd to the timer wheel so we continue trying wait HandshakeTryInterval * counter longer for next try
+		if !lighthouseTriggered {
 			//l.Infoln("Interval: ", HandshakeTryInterval*time.Duration(hostinfo.HandshakeCounter))
 			c.OutboundHandshakeTimer.Add(vpnIP, c.config.tryInterval*time.Duration(hostinfo.HandshakeCounter))
+		}
 	} else {
 		c.pendingHostMap.DeleteVpnIP(vpnIP)
 		c.pendingHostMap.DeleteIndex(index)
 	}
 }
-}
 
 func (c *HandshakeManager) NextInboundHandshakeTimerTick(now time.Time) {
 	c.InboundHandshakeTimer.advance(now)
@@ -169,6 +200,15 @@ func (c *HandshakeManager) AddVpnIP(vpnIP uint32) *HostInfo {
 	// We lock here and use an array to insert items to prevent locking the
 	// main receive thread for very long by waiting to add items to the pending map
 	c.OutboundHandshakeTimer.Add(vpnIP, c.config.tryInterval)
+
+	// If this is a static host, we don't need to wait for the HostQueryReply
+	// We can trigger the handshake right now
+	if _, ok := c.lightHouse.staticList[vpnIP]; ok {
+		select {
+		case c.trigger <- vpnIP:
+		default:
+		}
+	}
 	return hostinfo
 }
 

handshake_manager_test.go

@@ -103,6 +103,56 @@ func Test_NewHandshakeManagerVpnIP(t *testing.T) {
 	}
 }
 
+func Test_NewHandshakeManagerTrigger(t *testing.T) {
+	_, tuncidr, _ := net.ParseCIDR("172.1.1.1/24")
+	_, vpncidr, _ := net.ParseCIDR("172.1.1.1/24")
+	_, localrange, _ := net.ParseCIDR("10.1.1.1/24")
+	ip := ip2int(net.ParseIP("172.1.1.2"))
+	preferredRanges := []*net.IPNet{localrange}
+	mw := &mockEncWriter{}
+	mainHM := NewHostMap("test", vpncidr, preferredRanges)
+	lh := &LightHouse{}
+
+	blah := NewHandshakeManager(tuncidr, preferredRanges, mainHM, lh, &udpConn{}, defaultHandshakeConfig)
+
+	now := time.Now()
+	blah.NextOutboundHandshakeTimerTick(now, mw)
+
+	assert.Equal(t, 0, testCountTimerWheelEntries(blah.OutboundHandshakeTimer))
+
+	blah.AddVpnIP(ip)
+
+	assert.Equal(t, 1, testCountTimerWheelEntries(blah.OutboundHandshakeTimer))
+
+	// Trigger the same method the channel will
+	blah.handleOutbound(ip, mw, true)
+
+	// Make sure the trigger doesn't schedule another timer entry
+	assert.Equal(t, 1, testCountTimerWheelEntries(blah.OutboundHandshakeTimer))
+	hi := blah.pendingHostMap.Hosts[ip]
+	assert.Nil(t, hi.remote)
+
+	lh.addrMap = map[uint32][]udpAddr{
+		ip: {*NewUDPAddrFromString("10.1.1.1:4242")},
+	}
+
+	// This should trigger the hostmap to populate the hostinfo
+	blah.handleOutbound(ip, mw, true)
+	assert.NotNil(t, hi.remote)
+	assert.Equal(t, 1, testCountTimerWheelEntries(blah.OutboundHandshakeTimer))
+}
+
+func testCountTimerWheelEntries(tw *SystemTimerWheel) (c int) {
+	for _, i := range tw.wheel {
+		n := i.Head
+		for n != nil {
+			c++
+			n = n.Next
+		}
+	}
+	return c
+}
+
 func Test_NewHandshakeManagerVpnIPcleanup(t *testing.T) {
 	_, tuncidr, _ := net.ParseCIDR("172.1.1.1/24")
 	_, vpncidr, _ := net.ParseCIDR("172.1.1.1/24")

lighthouse.go

@@ -30,6 +30,9 @@ type LightHouse struct {
 	// filters local addresses that we advertise to lighthouses
 	localAllowList *AllowList
 
+	// used to trigger the HandshakeManager when we receive HostQueryReply
+	handshakeTrigger chan<- uint32
+
 	// staticList exists to avoid having a bool in each addrMap entry
 	// since static should be rare
 	staticList  map[uint32]struct{}
@@ -358,6 +361,11 @@ func (lh *LightHouse) HandleRequest(rAddr *udpAddr, vpnIp uint32, p []byte, c *c
 			ans := NewUDPAddr(a.Ip, uint16(a.Port))
 			lh.AddRemote(n.Details.VpnIp, ans, false)
 		}
+		// Non-blocking attempt to trigger, skip if it would block
+		select {
+		case lh.handshakeTrigger <- n.Details.VpnIp:
+		default:
+		}
 
 	case NebulaMeta_HostUpdateNotification:
 		//Simple check that the host sent this not someone else

main.go

@@ -321,11 +321,13 @@ func Main(config *Config, configTest bool, block bool, buildVersion string, logg
 		tryInterval:   config.GetDuration("handshakes.try_interval", DefaultHandshakeTryInterval),
 		retries:       config.GetInt("handshakes.retries", DefaultHandshakeRetries),
 		waitRotation:  config.GetInt("handshakes.wait_rotation", DefaultHandshakeWaitRotation),
+		triggerBuffer: config.GetInt("handshakes.trigger_buffer", DefaultHandshakeTriggerBuffer),
 
 		messageMetrics: messageMetrics,
 	}
 
 	handshakeManager := NewHandshakeManager(tunCidr, preferredRanges, hostMap, lightHouse, udpServer, handshakeConfig)
+	lightHouse.handshakeTrigger = handshakeManager.trigger
 
 	//TODO: These will be reused for psk
 	//handshakeMACKey := config.GetString("handshake_mac.key", "")