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feat: retry on DNS queries. #1180

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feat: retry on DNS queries. #1180

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feat: retry on DNS queries.
ldez Jun 3, 2020
d7b4336
review: rename errG.
ldez Jun 9, 2020
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34 changes: 30 additions & 4 deletions challenge/dns01/nameserver.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,8 @@ import (
"sync"
"time"

"github.com/cenkalti/backoff/v4"
"github.com/go-acme/lego/v3/log"
"github.com/miekg/dns"
)

Expand Down Expand Up @@ -229,15 +231,39 @@ 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 = 4 * bo.InitialInterval
Comment on lines +239 to +241
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@dmke dmke Jun 8, 2020

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This sets the max. wait time to 2 minutes if I invoke lego with --dns-timeout=30, doesn't it? Should bo.InitialInterval be dnsTimeout/4 instead?

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@ldez ldez Jun 8, 2020 •
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The initial interval must be the same as the timeout use by the DNS client.

The dnsTimeout cannot be used as MaxElapsedTime because it can be too short with the current value.

Currently dnsTimeout is the timeout for one DNS query.

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@dmke dmke Jun 9, 2020

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The initial interval must be the same as the timeout use by the DNS client

I see. Then the documentation of the --dns-timeout flag needs to be modified to something like "this is the minimum timeout given to resolve SOA queries; on network errors the actual timeout might be considerably longer".

Alternatively, we can reduce the default timeout down to something like 2 or 3s to approximate the previous behaviour (on that note, this should work in most cases, because DNS usually resolves fast enough). To accommodate #1008, we could also bump bo.MaxInterval and bo.MaxElapsedTime to 10*initialInterval and 20*initialInterval respectively.

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@ldez ldez Jun 9, 2020 •
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I can reduce the default timeout.

But I think that multiply by 10 or 20 is too big: the dnsQuery is used by several functions in a loop (by example a loop on ns) and this can become very very long.

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@dmke dmke Jun 9, 2020

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Oh, I've missed the context; I thought this was part of the fetchSoaByFqdn methods. Sorry for the confusion on my part.


operation := func() error {
var err error
in, err = sendDNSQuery(m, ns)

// errors from miekg/dns package and some errors from the net package must stop the retry.
var e *dns.Error
if err != nil &&
(strings.Contains(err.Error(), "connection refused") || errors.As(err, &e)) {
return backoff.Permanent(err)
}

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 {
Expand Down