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feat(secondary): add fallthrough support (#8041)

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This commit is contained in:
Ville Vesilehto
2026-05-20 10:13:03 +03:00
committed by GitHub
parent b1a7fc8db1
commit f8dffa7fc2
4 changed files with 187 additions and 8 deletions
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6
plugin/secondary/README.md
View File

@@ -27,6 +27,7 @@ A working syntax would be:
~~~
secondary [zones...] {
transfer from ADDRESS [ADDRESS...]
fallthrough [ZONES...]
}
~~~
@@ -34,6 +35,11 @@ secondary [zones...] {
times; if one does not work, another will be tried. Transferring this zone outwards again can be
done by enabling the *transfer* plugin.
* `fallthrough` If a query for a record in the zone results in NXDOMAIN, the query will be passed
to the next plugin in the chain. If **[ZONES...]** are listed, then only queries for those zones
will be subject to fallthrough. This can be useful in split DNS setups where the secondary zone
contains only partial records.
When a zone is due to be refreshed (refresh timer fires) a random jitter of 5 seconds is applied,
before fetching. In the case of retry this will be 2 seconds. If there are any errors during the
transfer in, the transfer fails; this will be logged.

18
plugin/secondary/setup.go
View File

@@ -7,6 +7,7 @@ import (
"github.com/coredns/coredns/core/dnsserver"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/file"
"github.com/coredns/coredns/plugin/pkg/fall"
clog "github.com/coredns/coredns/plugin/pkg/log"
"github.com/coredns/coredns/plugin/pkg/parse"
"github.com/coredns/coredns/plugin/pkg/upstream"
@@ -18,12 +19,12 @@ var log = clog.NewWithPlugin("secondary")
func init() { plugin.Register("secondary", setup) }
func setup(c *caddy.Controller) error {
zones, err := secondaryParse(c)
zones, fall, err := secondaryParse(c)
if err != nil {
return plugin.Error("secondary", err)
}
s := &Secondary{file.File{Zones: zones}}
s := &Secondary{file.File{Zones: zones, Fall: fall}}
var x *transfer.Transfer
c.OnStartup(func() error {
t := dnsserver.GetConfig(c).Handler("transfer")
@@ -84,9 +85,10 @@ func setup(c *caddy.Controller) error {
return nil
}
func secondaryParse(c *caddy.Controller) (file.Zones, error) {
func secondaryParse(c *caddy.Controller) (file.Zones, fall.F, error) {
z := make(map[string]*file.Zone)
names := []string{}
fall := fall.F{}
for c.Next() {
if c.Val() == "secondary" {
// secondary [origin]
@@ -105,11 +107,13 @@ func secondaryParse(c *caddy.Controller) (file.Zones, error) {
var err error
f, err = parse.TransferIn(c)
if err != nil {
return file.Zones{}, err
return file.Zones{}, fall, err
}
hasTransfer = true
case "fallthrough":
fall.SetZonesFromArgs(c.RemainingArgs())
default:
return file.Zones{}, c.Errf("unknown property '%s'", c.Val())
return file.Zones{}, fall, c.Errf("unknown property '%s'", c.Val())
}
for _, origin := range origins {
@@ -120,9 +124,9 @@ func secondaryParse(c *caddy.Controller) (file.Zones, error) {
}
}
if !hasTransfer {
return file.Zones{}, c.Err("secondary zones require a transfer from property")
return file.Zones{}, fall, c.Err("secondary zones require a transfer from property")
}
}
}
return file.Zones{Z: z, Names: names}, nil
return file.Zones{Z: z, Names: names}, fall, nil
}

34
plugin/secondary/setup_test.go
View File

@@ -4,6 +4,7 @@ import (
"testing"
"github.com/coredns/caddy"
"github.com/coredns/coredns/plugin/pkg/fall"
)
func TestSecondaryParse(t *testing.T) {
@@ -12,6 +13,7 @@ func TestSecondaryParse(t *testing.T) {
shouldErr bool
transferFrom string
zones []string
fall fall.F
}{
{
`secondary {
@@ -20,6 +22,7 @@ func TestSecondaryParse(t *testing.T) {
false,
"127.0.0.1:53",
nil,
fall.F{},
},
{
`secondary example.org {
@@ -28,12 +31,14 @@ func TestSecondaryParse(t *testing.T) {
false,
"127.0.0.1:53",
[]string{"example.org."},
fall.F{},
},
{
`secondary`,
true,
"",
nil,
fall.F{},
},
{
`secondary example.org {
@@ -42,12 +47,35 @@ func TestSecondaryParse(t *testing.T) {
true,
"",
nil,
fall.F{},
},
// fallthrough: bare (all zones)
{
`secondary {
transfer from 127.0.0.1
fallthrough
}`,
false,
"127.0.0.1:53",
nil,
fall.Root,
},
// fallthrough: specific zone
{
`secondary example.org {
transfer from 127.0.0.1
fallthrough example.org
}`,
false,
"127.0.0.1:53",
[]string{"example.org."},
fall.F{Zones: []string{"example.org."}},
},
}
for i, test := range tests {
c := caddy.NewTestController("dns", test.inputFileRules)
s, err := secondaryParse(c)
s, f, err := secondaryParse(c)
if err == nil && test.shouldErr {
t.Fatalf("Test %d expected errors, but got no error", i)
@@ -67,5 +95,9 @@ func TestSecondaryParse(t *testing.T) {
t.Fatalf("Test %d transform from names don't match expected %q, but got %q", i, test.transferFrom, x)
}
}
if !f.Equal(test.fall) {
t.Fatalf("Test %d fallthrough not equal: expected %v, got %v", i, test.fall, f)
}
}
}

137
test/secondary_test.go
View File

@@ -10,6 +10,143 @@ import (
"github.com/miekg/dns"
)
func TestSecondaryFallthrough(t *testing.T) {
// Create zone file for primary - has www.example.org A 127.0.0.1
primaryZone, rm1, err := test.TempFile(".", `$ORIGIN example.org.
@ 3600 IN SOA sns.dns.icann.org. noc.dns.icann.org. (
2017042745 ; serial
7200 ; refresh (2 hours)
3600 ; retry (1 hour)
1209600 ; expire (2 weeks)
3600 ; minimum (1 hour)
)
3600 IN NS a.iana-servers.net.
3600 IN NS b.iana-servers.net.
www IN A 127.0.0.1
`)
if err != nil {
t.Fatalf("Failed to create primary zone: %s", err)
}
defer rm1()
// Create zone file for fallback server - has other.example.org A 10.10.10.10
fallbackZone, rm2, err := test.TempFile(".", `$ORIGIN example.org.
@ 3600 IN SOA sns.dns.icann.org. noc.dns.icann.org. (
2017042745 ; serial
7200 ; refresh (2 hours)
3600 ; retry (1 hour)
1209600 ; expire (2 weeks)
3600 ; minimum (1 hour)
)
3600 IN NS a.iana-servers.net.
3600 IN NS b.iana-servers.net.
other IN A 10.10.10.10
`)
if err != nil {
t.Fatalf("Failed to create fallback zone: %s", err)
}
defer rm2()
// Start primary server (serves zone via AXFR)
primaryCorefile := `example.org:0 {
file ` + primaryZone + `
transfer {
to *
}
}`
primary, _, primaryTCP, err := CoreDNSServerAndPorts(primaryCorefile)
if err != nil {
t.Fatalf("Could not get primary CoreDNS instance: %s", err)
}
defer primary.Stop()
// Start fallback server (answers queries forwarded by secondary)
fallbackCorefile := `example.org:0 {
file ` + fallbackZone + `
}`
fallback, fallbackUDP, _, err := CoreDNSServerAndPorts(fallbackCorefile)
if err != nil {
t.Fatalf("Could not get fallback CoreDNS instance: %s", err)
}
defer fallback.Stop()
// Start secondary with fallthrough + forward to fallback
secondaryCorefile := `example.org:0 {
secondary {
transfer from ` + primaryTCP + `
fallthrough
}
forward . ` + fallbackUDP + `
}`
sec, secUDP, _, err := CoreDNSServerAndPorts(secondaryCorefile)
if err != nil {
t.Fatalf("Could not get secondary CoreDNS instance: %s", err)
}
defer sec.Stop()
// Wait for zone transfer to complete
m := new(dns.Msg)
m.SetQuestion("example.org.", dns.TypeSOA)
var r *dns.Msg
for range 10 {
r, _ = dns.Exchange(m, secUDP)
if r != nil && len(r.Answer) != 0 {
break
}
time.Sleep(100 * time.Millisecond)
}
if r == nil || len(r.Answer) == 0 {
t.Fatal("Zone transfer did not complete")
}
// Test 1: www.example.org exists in secondary zone - should return answer from zone
m = new(dns.Msg)
m.SetQuestion("www.example.org.", dns.TypeA)
r, err = dns.Exchange(m, secUDP)
if err != nil {
t.Fatalf("Expected to receive reply for www.example.org, but got error: %s", err)
}
if r.Rcode != dns.RcodeSuccess {
t.Fatalf("Expected NOERROR for www.example.org, got %s", dns.RcodeToString[r.Rcode])
}
if len(r.Answer) != 1 {
t.Fatalf("Expected 1 answer for www.example.org, got %d", len(r.Answer))
}
a, ok := r.Answer[0].(*dns.A)
if !ok {
t.Fatalf("Expected A record for www.example.org, got %T", r.Answer[0])
}
if a.A.String() != "127.0.0.1" {
t.Fatalf("Expected www.example.org to be 127.0.0.1, got %s", a.A.String())
}
// Test 2: other.example.org does NOT exist in secondary zone
// With fallthrough, query should pass to forward plugin which queries fallback server
m = new(dns.Msg)
m.SetQuestion("other.example.org.", dns.TypeA)
r, err = dns.Exchange(m, secUDP)
if err != nil {
t.Fatalf("Expected to receive reply for other.example.org, but got error: %s", err)
}
if r.Rcode != dns.RcodeSuccess {
t.Fatalf("Expected NOERROR for fallthrough query other.example.org, got %s", dns.RcodeToString[r.Rcode])
}
if len(r.Answer) != 1 {
t.Fatalf("Expected 1 answer from fallback for other.example.org, got %d", len(r.Answer))
}
a, ok = r.Answer[0].(*dns.A)
if !ok {
t.Fatalf("Expected A record from fallback for other.example.org, got %T", r.Answer[0])
}
if a.A.String() != "10.10.10.10" {
t.Fatalf("Expected fallback answer 10.10.10.10, got %s", a.A.String())
}
}
func TestEmptySecondaryZone(t *testing.T) {
// Corefile that fails to transfer example.org.
corefile := `example.org:0 {