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Better interface selection heuristic #3546

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merged 4 commits into from
Nov 15, 2017
Merged

Better interface selection heuristic #3546

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35cb143
Better interface selection heuristic
dadgar Nov 13, 2017
00557af
Use interface attached to default route
dadgar Nov 15, 2017
8ebca4b
use revised wording
dadgar Nov 15, 2017
6a434bc
changelog
dadgar Nov 15, 2017
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56 changes: 49 additions & 7 deletions client/fingerprint/network.go
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Original file line number Diff line number Diff line change
Expand Up @@ -187,7 +187,6 @@ func (n *NetworkFingerprint) isDeviceLoopBackOrPointToPoint(intf *net.Interface)
// and finds one which is routable and marked as UP
// It excludes PPP and lo devices unless they are specifically asked
func (f *NetworkFingerprint) findInterface(deviceName string) (*net.Interface, error) {
var interfaces []net.Interface
var err error

if deviceName != "" {
Expand All @@ -200,14 +199,57 @@ func (f *NetworkFingerprint) findInterface(deviceName string) (*net.Interface, e
return nil, err
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One of the comments on the PR indicated that the returned list here is not stable (can return things out of order). What happens if there is more than one interface with a global unicast address, thus resulting in them getting the same score?
Reading the code below, it seems like it will choose the first one, but if the order changes when calling interfaceDetector.Interfaces() that will change the results.

}

// Since we aren't given an interface to use we have to pick using a
// heuristic. To choose between interfaces we avoid down interfaces, those
// that are loopback, point to point, or don't have an address. Of the
// remaining interfaces we rank them positively for each global unicast
// address and slightly negatively for a link local address. This makes
// us select interfaces that have more globally routable address over those
// that do not.
var bestChoice *net.Interface
bestScore := -1000
for _, intf := range intfs {
if f.isDeviceEnabled(&intf) && !f.isDeviceLoopBackOrPointToPoint(&intf) && f.deviceHasIpAddress(&intf) {
interfaces = append(interfaces, intf)
// We require a non-loopback interface that is enabled with a valid
// address.
if !f.isDeviceEnabled(&intf) || f.isDeviceLoopBackOrPointToPoint(&intf) || !f.deviceHasIpAddress(&intf) {
continue
}

addrs, err := f.interfaceDetector.Addrs(&intf)
if err != nil {
return nil, err
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🤔 We could WARN and continue here, but after peeking at the Addrs(...) code it seems like all of the errors it returns indicate pretty bad syscall failures. Seems like just bailing is probably safest as users can manually set this anyway.

}
}

if len(interfaces) == 0 {
return nil, nil
seenLinkLocal := false
intfScore := 0
for _, addr := range addrs {
// Find the IP Addr and the CIDR from the Address
var ip net.IP
switch v := (addr).(type) {
case *net.IPNet:
ip = v.IP
case *net.IPAddr:
ip = v.IP
}

if !seenLinkLocal && (ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast()) {
intfScore -= 1
seenLinkLocal = true
}

if ip.IsGlobalUnicast() {
intfScore += 2
}
}

if intfScore > bestScore {
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@preetapan preetapan Nov 14, 2017 •
edited

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If infscore stays at zero and bestScore at -1000 this will pick the first intf from the intfs list, is that acceptable?

// Make a copy on the stack so we grab a pointer to the correct
// interface
local := intf
bestChoice = &local
bestScore = intfScore
}
}
return &interfaces[0], nil

return bestChoice, nil
}
7 changes: 5 additions & 2 deletions client/fingerprint/network_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,8 @@ type NetworkInterfaceDetectorMultipleInterfaces struct {
}

func (n *NetworkInterfaceDetectorMultipleInterfaces) Interfaces() ([]net.Interface, error) {
return []net.Interface{lo, eth0, eth1, eth2}, nil
// Return link local first to test we don't prefer it
return []net.Interface{eth3, lo, eth0, eth1, eth2, eth4}, nil
}

func (n *NetworkInterfaceDetectorMultipleInterfaces) InterfaceByName(name string) (*net.Interface, error) {
Expand Down Expand Up @@ -301,7 +302,9 @@ func TestNetworkFingerPrint_default_device(t *testing.T) {
}
}

func TestNetworkFingerPrint_excludelo_down_interfaces(t *testing.T) {
// This tests that we prefer skipping link local and down interfaces as well as
// those without global unicast addresses
func TestNetworkFingerPrint_preferential_interfaces(t *testing.T) {
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I don't see how any of these tests are exercising the new code path with the scoring introduced above.
I realize its not possible to test in a portable way across machines, but I would try to refactor the code so the scoring/selection logic is testable

f := &NetworkFingerprint{logger: testLogger(), interfaceDetector: &NetworkInterfaceDetectorMultipleInterfaces{}}
node := &structs.Node{
Attributes: make(map[string]string),
Expand Down