feat: retry on DNS queries.

challenge/dns01/nameserver.go

@@ -8,6 +8,8 @@ import (
  "sync"
  "time"
 
+ "github.com/cenkalti/backoff/v4"
+ "github.com/go-acme/lego/v3/log"
  "github.com/miekg/dns"
 )
 
@@ -229,15 +231,31 @@ func dnsQuery(fqdn string, rtype uint16, nameservers []string, recursive bool) (
  m := createDNSMsg(fqdn, rtype, recursive)
 
  var in *dns.Msg
- var err error
+ var errG error
 
  for _, ns := range nameservers {
- in, err = sendDNSQuery(m, ns)
- if err == nil && len(in.Answer) > 0 {
+ bo := backoff.NewExponentialBackOff()
+ bo.Multiplier = 1.2
+ bo.InitialInterval = dnsTimeout
+ bo.MaxInterval = 2 * bo.InitialInterval
+ bo.MaxElapsedTime = 6 * bo.InitialInterval
+
+ operation := func() error {
+ var err error
+ in, err = sendDNSQuery(m, ns)
+ return err
+ }
+
+ notify := func(err error, d time.Duration) {
+ log.Infof("dnsQuery retry %v: fqdn=%s, ns=%s: %v", d, fqdn, ns, err)
+ }
+
+ errG = backoff.RetryNotify(operation, bo, notify)
+ if errG == nil && len(in.Answer) > 0 {
  break
  }
  }
- return in, err
+ return in, errG
 }
 
 func createDNSMsg(fqdn string, rtype uint16, recursive bool) *dns.Msg {