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Don't overwrite old DNS results with empty list #1260

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Don't overwrite old DNS results with empty list #1260

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2 changes: 1 addition & 1 deletion lighthouse.go
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Original file line number Diff line number Diff line change
Expand Up @@ -545,7 +545,7 @@ func (lh *LightHouse) addStaticRemotes(i int, d time.Duration, network string, t
ctx := lh.ctx
lh.Unlock()

hr, err := NewHostnameResults(ctx, lh.l, d, network, timeout, toAddrs, func() {
hr, err := NewHostnamesResults(ctx, lh.l, d, vpnIp, network, timeout, toAddrs, func() {
// This callback runs whenever the DNS hostname resolver finds a different set of IP's
// in its resolution for hostnames.
am.Lock()
Expand Down
41 changes: 24 additions & 17 deletions remote_list.go
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Original file line number Diff line number Diff line change
Expand Up @@ -68,11 +68,12 @@ type hostnamesResults struct {
network string
lookupTimeout time.Duration
cancelFn func()
l *logrus.Logger
l logrus.FieldLogger
ips atomic.Pointer[map[netip.AddrPort]struct{}]
}

func NewHostnameResults(ctx context.Context, l *logrus.Logger, d time.Duration, network string, timeout time.Duration, hostPorts []string, onUpdate func()) (*hostnamesResults, error) {
func NewHostnamesResults(ctx context.Context, l logrus.FieldLogger, d time.Duration, vpnIp netip.Addr, network string, timeout time.Duration, hostPorts []string, onUpdate func()) (*hostnamesResults, error) {
l = l.WithField("vpnIp", vpnIp)
r := &hostnamesResults{
hostnames: make([]hostnamePort, len(hostPorts)),
network: network,
Expand Down Expand Up @@ -130,27 +131,33 @@ func NewHostnameResults(ctx context.Context, l *logrus.Logger, d time.Duration,
netipAddrs[netip.AddrPortFrom(a.Unmap(), hostPort.port)] = struct{}{}
}
}

origSet := r.ips.Load()
different := false
for a := range *origSet {
if _, ok := netipAddrs[a]; !ok {
different = true
break
}
}
if !different {
for a := range netipAddrs {
if _, ok := (*origSet)[a]; !ok {
if len(netipAddrs) == 0 && len(*origSet) != 0 {
l.WithFields(logrus.Fields{"hostnames": r.hostnames}).Info("No IPs resolved for hostnames, refusing to overwrite existing IPs")
Comment on lines +136 to +137
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I'm not sure how to behave in this scenario. LookupNetIP is asking the local resolver to either perform the DNS lookup or return its cached results. If it fails, then presumably there are no cached results because the TTL has expired. Should we keep hitting IPs when the TTL from prior queries has expired?
We could consider doing something else - Fast re-query on lookup errors? User could double the DNS lookup timeout? Or, never remove IPs from the list, just keep hitting whatever IPs we learned in the past? (I believe this is how the static IPs work today on reconfigs.)

} else {
different := false
for a := range *origSet {
if _, ok := netipAddrs[a]; !ok {
different = true
break
}
}
if !different {
for a := range netipAddrs {
if _, ok := (*origSet)[a]; !ok {
different = true
break
}
}
}
if different {
l.WithFields(logrus.Fields{"origSet": origSet, "newSet": netipAddrs}).Info("DNS results changed for host list")
r.ips.Store(&netipAddrs)
onUpdate()
}
}
if different {
l.WithFields(logrus.Fields{"origSet": origSet, "newSet": netipAddrs}).Info("DNS results changed for host list")
r.ips.Store(&netipAddrs)
onUpdate()
}

select {
case <-newCtx.Done():
return
Expand Down
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