/
dns.go
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/
dns.go
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package util
import (
"fmt"
"net"
"sync"
"time"
"github.com/miekg/dns"
utilruntime "k8s.io/apimachinery/pkg/util/runtime"
"k8s.io/apimachinery/pkg/util/sets"
"k8s.io/klog/v2"
"github.com/ovn-org/ovn-kubernetes/go-controller/pkg/config"
)
const (
// defaultTTL is used if an invalid or zero TTL is provided.
defaultTTL = 30 * time.Minute
)
type dnsValue struct {
// All IP addresses for a given domain name
ips []net.IP
// Time-to-live value from non-authoritative/cached name server for the domain
ttl time.Duration
// Holds (last dns lookup time + ttl), tells when to refresh IPs next time
nextQueryTime time.Time
}
type DNS struct {
// Protects dnsMap operations
lock sync.Mutex
// Holds dns name and its corresponding information
dnsMap map[string]dnsValue
// DNS resolvers
nameservers []string
// DNS port
port string
}
func NewDNS(resolverConfigFile string) (*DNS, error) {
config, err := dnsOps.ClientConfigFromFile(resolverConfigFile)
if err != nil || config == nil {
return nil, fmt.Errorf("cannot initialize the resolver: %v", err)
}
return &DNS{
dnsMap: map[string]dnsValue{},
nameservers: filterIPServers(config.Servers),
port: config.Port,
}, nil
}
func (d *DNS) Size() int {
d.lock.Lock()
defer d.lock.Unlock()
return len(d.dnsMap)
}
func (d *DNS) GetIPs(dns string) []net.IP {
d.lock.Lock()
defer d.lock.Unlock()
data := dnsValue{}
if res, ok := d.dnsMap[dns]; ok {
data.ips = make([]net.IP, len(res.ips))
copy(data.ips, res.ips)
data.ttl = res.ttl
data.nextQueryTime = res.nextQueryTime
}
return data.ips
}
func (d *DNS) Add(dns string) error {
d.lock.Lock()
defer d.lock.Unlock()
d.dnsMap[dns] = dnsValue{}
_, err := d.updateOne(dns)
if err != nil {
delete(d.dnsMap, dns)
}
return err
}
func (d *DNS) Delete(dns string) {
d.lock.Lock()
defer d.lock.Unlock()
delete(d.dnsMap, dns)
}
func (d *DNS) Update(dnsName string) (bool, error) {
d.lock.Lock()
defer d.lock.Unlock()
return d.updateOne(dnsName)
}
func (d *DNS) updateOne(dns string) (bool, error) {
res, ok := d.dnsMap[dns]
if !ok {
// Should not happen, all operations on dnsMap are synchronized by d.lock
return false, fmt.Errorf("DNS value not found in dnsMap for domain: %q", dns)
}
ips, ttl, err := d.getIPsAndMinTTL(dns)
if err != nil {
res.nextQueryTime = time.Now().Add(defaultTTL)
d.dnsMap[dns] = res
return false, err
}
changed := false
if !ipsEqual(res.ips, ips) {
changed = true
}
res.ips = ips
res.ttl = ttl
res.nextQueryTime = time.Now().Add(res.ttl)
d.dnsMap[dns] = res
return changed, nil
}
func (d *DNS) getIPsAndMinTTL(domain string) ([]net.IP, time.Duration, error) {
ips := []net.IP{}
ttlSet := false
var ttlSeconds uint32
var minTTL uint32
var recordTypes []uint16
if config.IPv4Mode {
recordTypes = append(recordTypes, dns.TypeA)
}
if config.IPv6Mode {
recordTypes = append(recordTypes, dns.TypeAAAA)
}
for _, recordType := range recordTypes {
for _, server := range d.nameservers {
msg := new(dns.Msg)
dnsOps.SetQuestion(msg, dnsOps.Fqdn(domain), recordType)
dialServer := server
if _, _, err := net.SplitHostPort(server); err != nil {
dialServer = net.JoinHostPort(server, d.port)
}
c := new(dns.Client)
c.Timeout = 5 * time.Second
in, _, err := dnsOps.Exchange(c, msg, dialServer)
if err != nil {
klog.Warningf("Failed to query nameserver: %s with address: %s for domain: %s, err: %v", server, dialServer, domain, err)
continue
}
if in.Truncated {
// if it was fall back on TCP
c.Net = "tcp"
// ensure that the old message is overwritten
msg = new(dns.Msg)
dnsOps.SetQuestion(msg, dnsOps.Fqdn(domain), recordType)
in_TCP, _, err := dnsOps.Exchange(c, msg, dialServer)
if err != nil {
klog.Warningf("Failed to fall back to TCP to get untruncated DNS results: for domain %s, err: %v", domain, err)
} else {
in = in_TCP
}
}
if in != nil && in.Rcode != dns.RcodeSuccess {
klog.Warningf("Failed to get a valid answer: %v from nameserver: %s for domain: %s", in.Rcode, server, domain)
continue
}
if in != nil && len(in.Answer) > 0 {
for _, a := range in.Answer {
if !ttlSet || a.Header().Ttl < ttlSeconds {
ttlSeconds = a.Header().Ttl
ttlSet = true
if minTTL == 0 {
minTTL = ttlSeconds
}
}
switch t := a.(type) {
case *dns.A:
ips = append(ips, t.A)
case *dns.AAAA:
ips = append(ips, t.AAAA)
}
}
if ttlSeconds < minTTL {
minTTL = ttlSeconds
}
}
}
}
if !ttlSet || (len(ips) == 0) {
return nil, defaultTTL, fmt.Errorf("IPv4 or IPv6 addr not found for domain: %q, nameservers: %v", domain, d.nameservers)
}
ttl, err := time.ParseDuration(fmt.Sprintf("%ds", minTTL))
if err != nil {
utilruntime.HandleError(fmt.Errorf("invalid TTL value for domain: %q, err: %v, defaulting ttl=%s", domain, err, defaultTTL.String()))
ttl = defaultTTL
}
if ttl == 0 {
ttl = defaultTTL
}
return removeDuplicateIPs(ips), ttl, nil
}
func (d *DNS) GetNextQueryTime() (time.Time, string, bool) {
d.lock.Lock()
defer d.lock.Unlock()
timeSet := false
var minTime time.Time
var dns string
for dnsName, res := range d.dnsMap {
if !timeSet || res.nextQueryTime.Before(minTime) {
timeSet = true
minTime = res.nextQueryTime
dns = dnsName
}
}
return minTime, dns, timeSet
}
func ipsEqual(oldips, newips []net.IP) bool {
if len(oldips) != len(newips) {
return false
}
for _, oldip := range oldips {
found := false
for _, newip := range newips {
if oldip.Equal(newip) {
found = true
break
}
}
if !found {
return false
}
}
return true
}
func filterIPServers(servers []string) []string {
ipServers := []string{}
for _, server := range servers {
if ip := net.ParseIP(server); ip != nil {
if ip.To4() != nil && config.IPv4Mode {
ipServers = append(ipServers, server)
} else if ip.To4() == nil && config.IPv6Mode {
// this is an ipv6 address
ipServers = append(ipServers, server)
}
}
}
return ipServers
}
func removeDuplicateIPs(ips []net.IP) []net.IP {
ipSet := sets.NewString()
uniqueIPs := []net.IP{}
for _, ip := range ips {
if !ipSet.Has(ip.String()) {
uniqueIPs = append(uniqueIPs, ip)
}
ipSet.Insert(ip.String())
}
return uniqueIPs
}