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fix(metrics): preserve request size from plugins (#7313)

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The rewrite plugin modifies DNS messages, affecting the request
size observed in the coredns_dns_request_size_bytes metric.

This change captures the original request size before any plugins
can modify it. It adds a functional options pattern to Report() to
pass this information while maintaining API compatibility.

Tests have been added to verify the fix prevents rewrite from
affecting the request size metrics.

Docs included.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
This commit is contained in:
Ville Vesilehto
2025-05-22 16:38:22 +03:00
committed by GitHub
parent 528cc26a4c
commit 32ea433a29
7 changed files with 337 additions and 15 deletions
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1
go.mod
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@@ -123,6 +123,7 @@ require (
github.com/jmespath/go-jmespath v0.4.0 // indirect
github.com/josharian/intern v1.0.0 // indirect
github.com/json-iterator/go v1.1.12 // indirect
github.com/kylelemons/godebug v1.1.0 // indirect
github.com/lufia/plan9stats v0.0.0-20240226150601-1dcf7310316a // indirect
github.com/mailru/easyjson v0.7.7 // indirect
github.com/mitchellh/go-homedir v1.1.0 // indirect

51
man/coredns-metrics.7
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@@ -1,5 +1,5 @@
.\" Generated by Mmark Markdown Processer - mmark.miek.nl
.TH "COREDNS-METRICS" 7 "March 2021" "CoreDNS" "CoreDNS Plugins"
.TH "COREDNS-METRICS" 7 "May 2025" "CoreDNS" "CoreDNS Plugins"
.SH "NAME"
.PP
@@ -10,30 +10,38 @@
.PP
With \fIprometheus\fP you export metrics from CoreDNS and any plugin that has them.
The default location for the metrics is \fB\fClocalhost:9153\fR. The metrics path is fixed to \fB\fC/metrics\fR.
The following metrics are exported:
.PP
In addition to the default Go metrics exported by the Prometheus Go client
\[la]https://prometheus.io/docs/guides/go-application/\[ra],
the following metrics are exported:
.IP \(bu 4
\fB\fCcoredns_build_info{version, revision, goversion}\fR - info about CoreDNS itself.
.IP \(bu 4
\fB\fCcoredns_panics_total{}\fR - total number of panics.
.IP \(bu 4
\fB\fCcoredns_dns_requests_total{server, zone, proto, family, type}\fR - total query count.
\fB\fCcoredns_dns_requests_total{server, zone, view, proto, family, type}\fR - total query count.
.IP \(bu 4
\fB\fCcoredns_dns_request_duration_seconds{server, zone, type}\fR - duration to process each query.
\fB\fCcoredns_dns_request_duration_seconds{server, zone, view, type}\fR - duration to process each query.
.IP \(bu 4
\fB\fCcoredns_dns_request_size_bytes{server, zone, proto}\fR - size of the request in bytes.
\fB\fCcoredns_dns_request_size_bytes{server, zone, view, proto}\fR - size of the request in bytes. Uses the original size before any plugin rewrites.
.IP \(bu 4
\fB\fCcoredns_dns_do_requests_total{server, zone}\fR - queries that have the DO bit set
\fB\fCcoredns_dns_do_requests_total{server, view, zone}\fR - queries that have the DO bit set
.IP \(bu 4
\fB\fCcoredns_dns_response_size_bytes{server, zone, proto}\fR - response size in bytes.
\fB\fCcoredns_dns_response_size_bytes{server, zone, view, proto}\fR - response size in bytes.
.IP \(bu 4
\fB\fCcoredns_dns_responses_total{server, zone, rcode}\fR - response per zone and rcode.
\fB\fCcoredns_dns_responses_total{server, zone, view, rcode, plugin}\fR - response per zone, rcode and plugin.
.IP \(bu 4
\fB\fCcoredns_plugin_enabled{server, zone, name}\fR - indicates whether a plugin is enabled on per server and zone basis.
\fB\fCcoredns_dns_https_responses_total{server, status}\fR - responses per server and http status code.
.IP \(bu 4
\fB\fCcoredns_dns_quic_responses_total{server, status}\fR - responses per server and QUIC application code.
.IP \(bu 4
\fB\fCcoredns_plugin_enabled{server, zone, view, name}\fR - indicates whether a plugin is enabled on per server, zone and view basis.
.PP
Each counter has a label \fB\fCzone\fR which is the zonename used for the request/response.
Almost each counter has a label \fB\fCzone\fR which is the zonename used for the request/response.
.PP
Extra labels used are:
@@ -48,14 +56,35 @@ this is \fB\fCdns://:53\fR. If you are using the \fIbind\fP plugin an IP address
The address family (\fB\fCfamily\fR) of the transport (1 = IP (IP version 4), 2 = IP6 (IP version 6)).
.IP \(bu 4
\fB\fCtype\fR which holds the query type. It holds most common types (A, AAAA, MX, SOA, CNAME, PTR, TXT,
NS, SRV, DS, DNSKEY, RRSIG, NSEC, NSEC3, IXFR, AXFR and ANY) and "other" which lumps together all
NS, SRV, DS, DNSKEY, RRSIG, NSEC, NSEC3, HTTPS, IXFR, AXFR and ANY) and "other" which lumps together all
other types.
.IP \(bu 4
\fB\fCstatus\fR which holds the https status code. Possible values are:
.RS
.IP \(en 4
200 - request is processed,
.IP \(en 4
404 - request has been rejected on validation,
.IP \(en 4
400 - request to dns message conversion failed,
.IP \(en 4
500 - processing ended up with no response.
.RE
.IP \(bu 4
the \fB\fCplugin\fR label holds the name of the plugin that made the write to the client. If the server
did the write (on error for instance), the value is empty.
.PP
If monitoring is enabled, queries that do not enter the plugin chain are exported under the fake
name "dropped" (without a closing dot - this is never a valid domain name).
.PP
Other plugins may export additional stats when the \fIprometheus\fP plugin is enabled. Those stats are documented in each
plugin's README.
.PP
This plugin can only be used once per Server Block.

2
plugin/metrics/README.md
View File

@@ -16,7 +16,7 @@ the following metrics are exported:
* `coredns_panics_total{}` - total number of panics.
* `coredns_dns_requests_total{server, zone, view, proto, family, type}` - total query count.
* `coredns_dns_request_duration_seconds{server, zone, view, type}` - duration to process each query.
* `coredns_dns_request_size_bytes{server, zone, view, proto}` - size of the request in bytes.
* `coredns_dns_request_size_bytes{server, zone, view, proto}` - size of the request in bytes. Uses the original size before any plugin rewrites.
* `coredns_dns_do_requests_total{server, view, zone}` - queries that have the DO bit set
* `coredns_dns_response_size_bytes{server, zone, view, proto}` - response size in bytes.
* `coredns_dns_responses_total{server, zone, view, rcode, plugin}` - response per zone, rcode and plugin.

7
plugin/metrics/handler.go
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@@ -16,6 +16,9 @@ import (
func (m *Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
state := request.Request{W: w, Req: r}
// Capture the original request size before any plugins modify it
originalSize := r.Len()
qname := state.QName()
zone := plugin.Zones(m.ZoneNames()).Matches(qname)
if zone == "" {
@@ -34,7 +37,9 @@ func (m *Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
rc = status
}
plugin := m.authoritativePlugin(rw.Caller)
vars.Report(WithServer(ctx), state, zone, WithView(ctx), rcode.ToString(rc), plugin, rw.Len, rw.Start)
// Pass the original request size to vars.Report
vars.Report(WithServer(ctx), state, zone, WithView(ctx), rcode.ToString(rc), plugin,
rw.Len, rw.Start, vars.WithOriginalReqSize(originalSize))
return status, err
}

34
plugin/metrics/vars/report.go
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@@ -6,10 +6,34 @@ import (
"github.com/coredns/coredns/request"
)
// ReportOptions is a struct that contains available options for the Report function.
type ReportOptions struct {
OriginalReqSize int
}
// ReportOption defines a function that modifies ReportOptions
type ReportOption func(*ReportOptions)
// WithOriginalReqSize returns an option to set the original request size
func WithOriginalReqSize(size int) ReportOption {
return func(opts *ReportOptions) {
opts.OriginalReqSize = size
}
}
// Report reports the metrics data associated with request. This function is exported because it is also
// called from core/dnsserver to report requests hitting the server that should not be handled and are thus
// not sent down the plugin chain.
func Report(server string, req request.Request, zone, view, rcode, plugin string, size int, start time.Time) {
func Report(server string, req request.Request, zone, view, rcode, plugin string,
size int, start time.Time, opts ...ReportOption) {
options := ReportOptions{
OriginalReqSize: 0,
}
for _, opt := range opts {
opt(&options)
}
// Proto and Family.
net := req.Proto()
fam := "1"
@@ -27,7 +51,13 @@ func Report(server string, req request.Request, zone, view, rcode, plugin string
RequestDuration.WithLabelValues(server, zone, view).Observe(time.Since(start).Seconds())
ResponseSize.WithLabelValues(server, zone, view, net).Observe(float64(size))
RequestSize.WithLabelValues(server, zone, view, net).Observe(float64(req.Len()))
reqSize := req.Len()
if options.OriginalReqSize > 0 {
reqSize = options.OriginalReqSize
}
RequestSize.WithLabelValues(server, zone, view, net).Observe(float64(reqSize))
ResponseRcode.WithLabelValues(server, zone, view, rcode, plugin).Inc()
}

101
plugin/metrics/vars/report_test.go Normal file
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@@ -0,0 +1,101 @@
package vars
import (
"testing"
"time"
"github.com/coredns/coredns/plugin/test"
"github.com/coredns/coredns/request"
"github.com/miekg/dns"
"github.com/prometheus/client_golang/prometheus/testutil"
)
func TestReportWithOptions(t *testing.T) {
tests := []struct {
name string
question string
qtype uint16
edns0 bool
do bool
originalSize int
useOriginal bool
}{
{
name: "A record without DO bit",
question: "example.org.",
qtype: dns.TypeA,
edns0: true,
do: false,
originalSize: 0,
useOriginal: false,
},
{
name: "A record with DO bit",
question: "example.org.",
qtype: dns.TypeA,
edns0: true,
do: true,
originalSize: 0,
useOriginal: false,
},
{
name: "A record with original size",
question: "example.org.",
qtype: dns.TypeA,
edns0: false,
do: false,
originalSize: 42,
useOriginal: true,
},
{
name: "A record bogus qtype",
question: "example.org.",
qtype: 0, // does not exist
edns0: false,
do: false,
originalSize: 42,
useOriginal: true,
},
}
for _, tc := range tests {
t.Run(tc.name, func(t *testing.T) {
m := new(dns.Msg)
m.SetQuestion(tc.question, tc.qtype)
if tc.edns0 {
m.SetEdns0(4096, tc.do)
}
w := &test.ResponseWriter{}
state := request.Request{W: w, Req: m}
if state.Do() != tc.do {
t.Errorf("DO bit detection failed, got %v, want %v", state.Do(), tc.do)
}
qType := qTypeString(tc.qtype)
expectedType := dns.Type(tc.qtype).String()
if qType != expectedType && qType != "other" {
t.Errorf("qTypeString(%d) = %s, want %s or 'other'", tc.qtype, qType, expectedType)
}
var opts []ReportOption
if tc.useOriginal {
opts = append(opts, WithOriginalReqSize(tc.originalSize))
}
net := state.Proto()
fam := "1"
countBefore := testutil.ToFloat64(RequestCount.WithLabelValues("dns://:53", "example.org.", "", net, fam, qType))
Report("dns://:53", state, "example.org.", "", "NOERROR", "test", 100, time.Now(), opts...)
countAfter := testutil.ToFloat64(RequestCount.WithLabelValues("dns://:53", "example.org.", "", net, fam, qType))
if countAfter <= countBefore {
t.Errorf("RequestCount was not incremented. Before: %f, After: %f", countBefore, countAfter)
}
})
}
}

156
test/metrics_test.go
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@@ -1,8 +1,11 @@
package test
import (
"fmt"
"os"
"path/filepath"
"reflect"
"strconv"
"strings"
"testing"
"time"
@@ -70,6 +73,159 @@ func TestMetricsRefused(t *testing.T) {
}
}
// getBucketCount extracts the count for a specific bucket from a metric family
func getBucketCount(mf *test.MetricFamily, bucketLabel string) (int, error) {
if mf == nil {
return 0, fmt.Errorf("metric family is nil")
}
if len(mf.Metrics) == 0 {
return 0, fmt.Errorf("metric family %s has no metrics", mf.Name)
}
// mf.Metrics[0] is an interface{} containing an unexported 'histogram' struct from plugin/test.
metricPoint := mf.Metrics[0]
val := reflect.ValueOf(metricPoint)
// Check if the underlying type is a struct (as histogram is)
if val.Kind() != reflect.Struct {
return 0, fmt.Errorf("metric point for %s is not a struct, but %s", mf.Name, val.Kind())
}
// Access the 'Buckets' field, which should be map[string]string
bucketsField := val.FieldByName("Buckets")
if !bucketsField.IsValid() {
return 0, fmt.Errorf("metric point for %s has no 'Buckets' field", mf.Name)
}
bucketsMap, ok := bucketsField.Interface().(map[string]string)
if !ok {
return 0, fmt.Errorf("'Buckets' field for %s is not a map[string]string", mf.Name)
}
countStr, ok := bucketsMap[bucketLabel]
if !ok {
// For these tests, we'll treat a missing bucket as 0.
return 0, nil
}
count, err := strconv.Atoi(countStr)
if err != nil {
return 0, fmt.Errorf("could not parse bucket count '%s' for %s: %v", countStr, mf.Name, err)
}
return count, nil
}
// extractRequestSizeBucketCounts extracts bucket counts from DNS request size metrics
func extractRequestSizeBucketCounts(t *testing.T, metrics []*test.MetricFamily, label string) (int, int, error) {
var countBelow100, countAbove100 int
var err error
for _, mf := range metrics {
if strings.Contains(mf.Name, "coredns_dns_request_size_bytes") {
t.Logf(" %s: %v", mf.Name, mf.Metrics)
countBelow100, err = getBucketCount(mf, "100")
if err != nil {
return 0, 0, fmt.Errorf("%s: error getting bucket count for 100: %v", label, err)
}
countAbove100, err = getBucketCount(mf, "1023")
if err != nil {
return 0, 0, fmt.Errorf("%s: error getting bucket count for 1023: %v", label, err)
}
return countBelow100, countAbove100, nil
}
}
return 0, 0, fmt.Errorf("%s: could not find coredns_dns_request_size_bytes metric", label)
}
func TestMetricsRewriteRequestSize(t *testing.T) {
// number of requests to send
numRequests := 5
// First test without rewrite
corefileWithoutRewrite := `.:0 {
prometheus localhost:0
forward . 8.8.8.8
}`
srv, udp, _, err := CoreDNSServerAndPorts(corefileWithoutRewrite)
if err != nil {
t.Fatalf("Could not get CoreDNS serving instance: %s", err)
}
// Create a DNS request with a long name to have a size close to 100 bytes
m := new(dns.Msg)
m.SetQuestion("somerequestthathaveasize90.123456789.123456789.123456789.example.com.", dns.TypeA)
expectedSize := 86
actualSize := m.Len()
if actualSize != expectedSize {
t.Fatalf("Expected request size %d, but got %d", expectedSize, actualSize)
}
// Send multiple requests
for i := 0; i < numRequests; i++ {
if _, err = dns.Exchange(m, udp); err != nil {
t.Fatalf("Could not send message: %s", err)
}
}
metricsWithoutRewrite := test.Scrape("http://" + metrics.ListenAddr + "/metrics")
t.Log("Available metrics without rewrite:")
countBelow100withoutRewrite, countAbove100withoutRewrite, err := extractRequestSizeBucketCounts(t, metricsWithoutRewrite, "without rewrite")
if err != nil {
t.Error(err)
}
// Stop the first server
srv.Stop()
time.Sleep(100 * time.Millisecond) // Give server time to clean up
// Now test with rewrite plugin
corefileWithRewrite := `.:0 {
prometheus localhost:0
rewrite edns0 local set 0x13 test123456 revert
forward . 8.8.8.8
}`
srv2, udp2, _, err := CoreDNSServerAndPorts(corefileWithRewrite)
if err != nil {
t.Fatalf("Could not get CoreDNS serving instance: %s", err)
}
defer srv2.Stop()
// Send the same requests with rewrite
for i := 0; i < numRequests; i++ {
if _, err = dns.Exchange(m, udp2); err != nil {
t.Fatalf("Could not send message: %s", err)
}
}
// Scrape metrics again
metricsWithRewrite := test.Scrape("http://" + metrics.ListenAddr + "/metrics")
t.Log("Available metrics with rewrite:")
countBelow100withRewrite, countAbove100withRewrite, err := extractRequestSizeBucketCounts(t, metricsWithRewrite, "with rewrite")
if err != nil {
t.Error(err)
}
// Both servers should record metrics in the same buckets regardless of the
// rewrite plugin's modifications. The original request size is 86 bytes,
// which falls into the le=100 bucket, before and after the rewrite.
if countBelow100withoutRewrite != countAbove100withoutRewrite &&
countBelow100withRewrite != countAbove100withRewrite {
t.Errorf("Expected all requests to go to le=100 bucket")
}
// The count in the le=100 bucket should be the same with or without rewrite.
// Second round of requests should go to le=100 bucket.
if countBelow100withRewrite != countBelow100withoutRewrite+numRequests {
t.Errorf("Expected all requests to go to le=100 bucket")
}
}
func TestMetricsAuto(t *testing.T) {
tmpdir := t.TempDir()