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Apply DNS host config on change only #4695

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Apply DNS host config on change only #4695

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22 changes: 22 additions & 0 deletions client/internal/dns/server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,7 @@ type DefaultServer struct {
updateSerial uint64
previousConfigHash uint64
currentConfig HostDNSConfig
currentConfigHash uint64
handlerChain *HandlerChain
extraDomains map[domain.Domain]int

Expand Down Expand Up @@ -207,6 +208,7 @@ func newDefaultServer(
hostsDNSHolder: newHostsDNSHolder(),
hostManager: &noopHostConfigurator{},
mgmtCacheResolver: mgmtCacheResolver,
currentConfigHash: ^uint64(0), // Initialize to max uint64 to ensure first config is always applied
}

// register with root zone, handler chain takes care of the routing
Expand Down Expand Up @@ -586,8 +588,28 @@ func (s *DefaultServer) applyHostConfig() {

log.Debugf("extra match domains: %v", maps.Keys(s.extraDomains))

hash, err := hashstructure.Hash(config, hashstructure.FormatV2, &hashstructure.HashOptions{
ZeroNil: true,
IgnoreZeroValue: true,
SlicesAsSets: true,
UseStringer: true,
})
if err != nil {
log.Warnf("unable to hash the host dns configuration, will apply config anyway: %s", err)
// Fall through to apply config anyway (fail-safe approach)
} else if s.currentConfigHash == hash {
log.Debugf("not applying host config as there are no changes")
return
}

if err := s.hostManager.applyDNSConfig(config, s.stateManager); err != nil {
log.Errorf("failed to apply DNS host manager update: %v", err)
return
}

// Only update hash if it was computed successfully and config was applied
if err == nil {
s.currentConfigHash = hash
}

s.registerFallback(config)
Expand Down
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