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dns.go
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dns.go
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package plugin
import (
"fmt"
"net"
"os/exec"
"strings"
"sync"
"time"
"github.com/golang/glog"
kerrors "k8s.io/apimachinery/pkg/util/errors"
kexec "k8s.io/kubernetes/pkg/util/exec"
)
const (
DIG = "dig"
defaultTTL = 30 * time.Minute
)
type dnsValue struct {
// All IPv4 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 {
// Runs shell commands
execer kexec.Interface
// Protects dnsMap operations
lock sync.Mutex
// Holds dns name and its corresponding information
dnsMap map[string]dnsValue
}
func CheckDNSResolver() error {
if _, err := exec.LookPath(DIG); err != nil {
return fmt.Errorf("%s is not installed", DIG)
}
return nil
}
func NewDNS(execer kexec.Interface) *DNS {
return &DNS{
execer: execer,
dnsMap: map[string]dnsValue{},
}
}
func (d *DNS) Size() int {
d.lock.Lock()
defer d.lock.Unlock()
return len(d.dnsMap)
}
func (d *DNS) Get(dns string) dnsValue {
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
}
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) Update() (error, bool) {
d.lock.Lock()
defer d.lock.Unlock()
errList := []error{}
changed := false
for dns := range d.dnsMap {
err, updated := d.updateOne(dns)
if err != nil {
errList = append(errList, err)
continue
}
if updated {
changed = true
}
}
return kerrors.NewAggregate(errList), changed
}
func (d *DNS) updateOne(dns string) (error, bool) {
// Due to lack of any go bindings for dns resolver that actually provides TTL value, we are relying on 'dig' shell command.
// Output Format:
// <domain-name>. <<ttl from authoritative ns> IN A <IP addr>
out, err := d.execer.Command(DIG, "+nocmd", "+noall", "+answer", "+ttlid", "a", dns).CombinedOutput()
if err != nil || len(out) == 0 {
return fmt.Errorf("Failed to fetch IP addr and TTL value for domain: %q, err: %v", dns, err), false
}
outStr := strings.Trim(string(out[:]), "\n")
res, ok := d.dnsMap[dns]
if !ok {
// Should not happen, all operations on dnsMap are synchronized by d.lock
return fmt.Errorf("DNS value not found in dnsMap for domain: %q", dns), false
}
var minTTL time.Duration
var ips []net.IP
for _, line := range strings.Split(outStr, "\n") {
fields := strings.Fields(line)
if len(fields) != 5 {
continue
}
ttl, err := time.ParseDuration(fmt.Sprintf("%ss", fields[1]))
if err != nil {
glog.Errorf("Invalid TTL value for domain: %q, err: %v, defaulting ttl=%s", dns, err, defaultTTL.String())
ttl = defaultTTL
}
if (minTTL.Seconds() == 0) || (minTTL.Seconds() > ttl.Seconds()) {
minTTL = ttl
}
ip := net.ParseIP(fields[4])
if ip != nil {
ips = append(ips, ip)
}
}
changed := false
if !ipsEqual(res.ips, ips) {
changed = true
}
res.ips = ips
res.ttl = minTTL
res.nextQueryTime = time.Now().Add(res.ttl)
d.dnsMap[dns] = res
return nil, changed
}
func (d *DNS) GetMinQueryTime() (time.Time, bool) {
d.lock.Lock()
defer d.lock.Unlock()
timeSet := false
var minTime time.Time
for _, res := range d.dnsMap {
if (timeSet == false) || res.nextQueryTime.Before(minTime) {
timeSet = true
minTime = res.nextQueryTime
}
}
return minTime, 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
}