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plugin/k8s_external: Resolve headless services (#5505)

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*add option for resolving headless Services without external IPs in k8s_external

Signed-off-by: Tomas Kohout <tomas.kohout1995@gmail.com>
This commit is contained in:
TomasKohout
2022-08-30 20:59:27 +02:00
committed by GitHub
parent b218b56063
commit 6782b7fb42
15 changed files with 491 additions and 81 deletions
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14
plugin/k8s_external/README.md
View File

@@ -2,12 +2,12 @@
## Name
*k8s_external* - resolves load balancer and external IPs from outside Kubernetes clusters.
*k8s_external* - resolves load balancer, external IPs from outside Kubernetes clusters and if enabled headless services.
## Description
This plugin allows an additional zone to resolve the external IP address(es) of a Kubernetes
service. This plugin is only useful if the *kubernetes* plugin is also loaded.
service and headless services. This plugin is only useful if the *kubernetes* plugin is also loaded.
The plugin uses an external zone to resolve in-cluster IP addresses. It only handles queries for A,
AAAA, SRV, and PTR records; all others result in NODATA responses. To make it a proper DNS zone, it handles
@@ -57,6 +57,16 @@ k8s_external [ZONE...] {
* **APEX** is the name (DNS label) to use for the apex records; it defaults to `dns`.
* `ttl` allows you to set a custom **TTL** for responses. The default is 5 (seconds).
If you want to enable headless service resolution, you can do so by adding `headless` option.
~~~
k8s_external [ZONE...] {
headless
}
~~~
* if there is a headless service with external IPs set, external IPs will be resolved
## Examples
Enable names under `example.org` to be resolved to in-cluster DNS addresses.

4
plugin/k8s_external/apex.go
View File

@@ -18,7 +18,7 @@ func (e *External) serveApex(state request.Request) (int, error) {
case dns.TypeNS:
m.Answer = []dns.RR{e.ns(state)}
addr := e.externalAddrFunc(state)
addr := e.externalAddrFunc(state, e.headless)
for _, rr := range addr {
rr.Header().Ttl = e.ttl
rr.Header().Name = dnsutil.Join("ns1", e.apex, state.QName())
@@ -58,7 +58,7 @@ func (e *External) serveSubApex(state request.Request) (int, error) {
return 0, nil
}
addr := e.externalAddrFunc(state)
addr := e.externalAddrFunc(state, e.headless)
for _, rr := range addr {
rr.Header().Ttl = e.ttl
rr.Header().Name = state.QName()

1
plugin/k8s_external/apex_test.go
View File

@@ -17,6 +17,7 @@ func TestApex(t *testing.T) {
k.APIConn = &external{}
e := New()
e.headless = true
e.Zones = []string{"example.com."}
e.Next = test.NextHandler(dns.RcodeSuccess, nil)
e.externalFunc = k.External

23
plugin/k8s_external/external.go
View File

@@ -26,11 +26,11 @@ import (
type Externaler interface {
// External returns a slice of msg.Services that are looked up in the backend and match
// the request.
External(request.Request) ([]msg.Service, int)
External(request.Request, bool) ([]msg.Service, int)
// ExternalAddress should return a string slice of addresses for the nameserving endpoint.
ExternalAddress(state request.Request) []dns.RR
// ExternalServices returns all services in the given zone as a slice of msg.Service.
ExternalServices(zone string) []msg.Service
ExternalAddress(state request.Request, headless bool) []dns.RR
// ExternalServices returns all services in the given zone as a slice of msg.Service and if enabled, headless services as a map of services.
ExternalServices(zone string, headless bool) ([]msg.Service, map[string][]msg.Service)
// ExternalSerial gets the current serial.
ExternalSerial(string) uint32
}
@@ -40,16 +40,17 @@ type External struct {
Next plugin.Handler
Zones []string
hostmaster string
apex string
ttl uint32
hostmaster string
apex string
ttl uint32
headless bool
upstream *upstream.Upstream
externalFunc func(request.Request) ([]msg.Service, int)
externalAddrFunc func(request.Request) []dns.RR
externalFunc func(request.Request, bool) ([]msg.Service, int)
externalAddrFunc func(request.Request, bool) []dns.RR
externalSerialFunc func(string) uint32
externalServicesFunc func(string) []msg.Service
externalServicesFunc func(string, bool) ([]msg.Service, map[string][]msg.Service)
}
// New returns a new and initialized *External.
@@ -85,7 +86,7 @@ func (e *External) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Ms
}
}
svc, rcode := e.externalFunc(state)
svc, rcode := e.externalFunc(state, e.headless)
m := new(dns.Msg)
m.SetReply(state.Req)

133
plugin/k8s_external/external_test.go
View File

@@ -21,6 +21,7 @@ func TestExternal(t *testing.T) {
e := New()
e.Zones = []string{"example.com.", "in-addr.arpa."}
e.headless = true
e.Next = test.NextHandler(dns.RcodeSuccess, nil)
e.externalFunc = k.External
e.externalAddrFunc = externalAddress // internal test function
@@ -216,18 +217,86 @@ var tests = []test.Case{
test.SRV("svc12.testns.example.com. 5 IN SRV 0 100 80 dummy.hostname."),
},
},
// headless service
{
Qname: "svc-headless.testns.example.com.", Qtype: dns.TypeA, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.A("svc-headless.testns.example.com. 5 IN A 1.2.3.4"),
test.A("svc-headless.testns.example.com. 5 IN A 1.2.3.5"),
},
},
{
Qname: "svc-headless.testns.example.com.", Qtype: dns.TypeSRV, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.SRV("svc-headless.testns.example.com. 5 IN SRV 0 50 80 endpoint-svc-0.svc-headless.testns.example.com."),
test.SRV("svc-headless.testns.example.com. 5 IN SRV 0 50 80 endpoint-svc-1.svc-headless.testns.example.com."),
},
Extra: []dns.RR{
test.A("endpoint-svc-0.svc-headless.testns.example.com. 5 IN A 1.2.3.4"),
test.A("endpoint-svc-1.svc-headless.testns.example.com. 5 IN A 1.2.3.5"),
},
},
{
Qname: "_http._tcp.svc-headless.testns.example.com.", Qtype: dns.TypeSRV, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.SRV("_http._tcp.svc-headless.testns.example.com. 5 IN SRV 0 50 80 endpoint-svc-0.svc-headless.testns.example.com."),
test.SRV("_http._tcp.svc-headless.testns.example.com. 5 IN SRV 0 50 80 endpoint-svc-1.svc-headless.testns.example.com."),
},
Extra: []dns.RR{
test.A("endpoint-svc-0.svc-headless.testns.example.com. 5 IN A 1.2.3.4"),
test.A("endpoint-svc-1.svc-headless.testns.example.com. 5 IN A 1.2.3.5"),
},
},
{
Qname: "endpoint-svc-0.svc-headless.testns.example.com.", Qtype: dns.TypeSRV, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.SRV("endpoint-svc-0.svc-headless.testns.example.com. 5 IN SRV 0 100 80 endpoint-svc-0.svc-headless.testns.example.com."),
},
Extra: []dns.RR{
test.A("endpoint-svc-0.svc-headless.testns.example.com. 5 IN A 1.2.3.4"),
},
},
{
Qname: "endpoint-svc-1.svc-headless.testns.example.com.", Qtype: dns.TypeSRV, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.SRV("endpoint-svc-1.svc-headless.testns.example.com. 5 IN SRV 0 100 80 endpoint-svc-1.svc-headless.testns.example.com."),
},
Extra: []dns.RR{
test.A("endpoint-svc-1.svc-headless.testns.example.com. 5 IN A 1.2.3.5"),
},
},
{
Qname: "endpoint-svc-0.svc-headless.testns.example.com.", Qtype: dns.TypeA, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.A("endpoint-svc-0.svc-headless.testns.example.com. 5 IN A 1.2.3.4"),
},
},
{
Qname: "endpoint-svc-1.svc-headless.testns.example.com.", Qtype: dns.TypeA, Rcode: dns.RcodeSuccess,
Answer: []dns.RR{
test.A("endpoint-svc-1.svc-headless.testns.example.com. 5 IN A 1.2.3.5"),
},
},
}
type external struct{}
func (external) HasSynced() bool { return true }
func (external) Run() {}
func (external) Stop() error { return nil }
func (external) EpIndexReverse(string) []*object.Endpoints { return nil }
func (external) SvcIndexReverse(string) []*object.Service { return nil }
func (external) Modified(bool) int64 { return 0 }
func (external) EpIndex(s string) []*object.Endpoints { return nil }
func (external) EndpointsList() []*object.Endpoints { return nil }
func (external) HasSynced() bool { return true }
func (external) Run() {}
func (external) Stop() error { return nil }
func (external) EpIndexReverse(string) []*object.Endpoints { return nil }
func (external) SvcIndexReverse(string) []*object.Service { return nil }
func (external) Modified(bool) int64 { return 0 }
func (external) EpIndex(s string) []*object.Endpoints {
return epIndexExternal[s]
}
func (external) EndpointsList() []*object.Endpoints {
var eps []*object.Endpoints
for _, ep := range epIndexExternal {
eps = append(eps, ep...)
}
return eps
}
func (external) GetNodeByName(ctx context.Context, name string) (*api.Node, error) { return nil, nil }
func (external) SvcIndex(s string) []*object.Service { return svcIndexExternal[s] }
func (external) PodIndex(string) []*object.Pod { return nil }
@@ -252,6 +321,41 @@ func (external) GetNamespaceByName(name string) (*object.Namespace, error) {
}, nil
}
var epIndexExternal = map[string][]*object.Endpoints{
"svc-headless.testns": {
{
Name: "svc-headless",
Namespace: "testns",
Index: "svc-headless.testns",
Subsets: []object.EndpointSubset{
{
Ports: []object.EndpointPort{
{
Port: 80,
Name: "http",
Protocol: "TCP",
},
},
Addresses: []object.EndpointAddress{
{
IP: "1.2.3.4",
Hostname: "endpoint-svc-0",
NodeName: "test-node",
TargetRefName: "endpoint-svc-0",
},
{
IP: "1.2.3.5",
Hostname: "endpoint-svc-1",
NodeName: "test-node",
TargetRefName: "endpoint-svc-1",
},
},
},
},
},
},
}
var svcIndexExternal = map[string][]*object.Service{
"svc1.testns": {
{
@@ -279,6 +383,7 @@ var svcIndexExternal = map[string][]*object.Service{
Namespace: "testns",
Type: api.ServiceTypeLoadBalancer,
ExternalIPs: []string{"2.3.4.5"},
ClusterIPs: []string{"10.0.0.3"},
Ports: []api.ServicePort{{Name: "http", Protocol: "tcp", Port: 80}},
},
},
@@ -287,10 +392,20 @@ var svcIndexExternal = map[string][]*object.Service{
Name: "svc12",
Namespace: "testns",
Type: api.ServiceTypeLoadBalancer,
ClusterIPs: []string{"10.0.0.3"},
ExternalIPs: []string{"dummy.hostname"},
Ports: []api.ServicePort{{Name: "http", Protocol: "tcp", Port: 80}},
},
},
"svc-headless.testns": {
{
Name: "svc-headless",
Namespace: "testns",
Type: api.ServiceTypeClusterIP,
ClusterIPs: []string{"None"},
Ports: []api.ServicePort{{Name: "http", Protocol: "tcp", Port: 80}},
},
},
}
func (external) ServiceList() []*object.Service {
@@ -301,7 +416,7 @@ func (external) ServiceList() []*object.Service {
return svcs
}
func externalAddress(state request.Request) []dns.RR {
func externalAddress(state request.Request, headless bool) []dns.RR {
a := test.A("example.org. IN A 127.0.0.1")
return []dns.RR{a}
}

2
plugin/k8s_external/setup.go
View File

@@ -68,6 +68,8 @@ func parse(c *caddy.Controller) (*External, error) {
return nil, c.ArgErr()
}
e.apex = args[0]
case "headless":
e.headless = true
default:
return nil, c.Errf("unknown property '%s'", c.Val())
}

23
plugin/k8s_external/setup_test.go
View File

@@ -8,16 +8,20 @@ import (
func TestSetup(t *testing.T) {
tests := []struct {
input string
shouldErr bool
expectedZone string
expectedApex string
input string
shouldErr bool
expectedZone string
expectedApex string
expectedHeadless bool
}{
{`k8s_external`, false, "", "dns"},
{`k8s_external example.org`, false, "example.org.", "dns"},
{`k8s_external`, false, "", "dns", false},
{`k8s_external example.org`, false, "example.org.", "dns", false},
{`k8s_external example.org {
apex testdns
}`, false, "example.org.", "testdns"},
}`, false, "example.org.", "testdns", false},
{`k8s_external example.org {
headless
}`, false, "example.org.", "dns", true},
}
for i, test := range tests {
@@ -44,5 +48,10 @@ func TestSetup(t *testing.T) {
t.Errorf("Test %d, expected apex %q for input %s, got: %q", i, test.expectedApex, test.input, e.apex)
}
}
if !test.shouldErr {
if test.expectedHeadless != e.headless {
t.Errorf("Test %d, expected headless %q for input %s, got: %v", i, test.expectedApex, test.input, e.headless)
}
}
}
}

57
plugin/k8s_external/transfer.go
View File

@@ -2,9 +2,11 @@ package external
import (
"context"
"strings"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/etcd/msg"
"github.com/coredns/coredns/plugin/kubernetes"
"github.com/coredns/coredns/plugin/transfer"
"github.com/coredns/coredns/request"
@@ -40,7 +42,7 @@ func (e *External) Transfer(zone string, serial uint32) (<-chan []dns.RR, error)
ch <- []dns.RR{&dns.NS{Hdr: nsHdr, Ns: nsName}}
// Add Nameserver A/AAAA records
nsRecords := e.externalAddrFunc(state)
nsRecords := e.externalAddrFunc(state, e.headless)
for i := range nsRecords {
// externalAddrFunc returns incomplete header names, correct here
nsRecords[i].Header().Name = nsName
@@ -48,10 +50,12 @@ func (e *External) Transfer(zone string, serial uint32) (<-chan []dns.RR, error)
ch <- []dns.RR{nsRecords[i]}
}
svcs := e.externalServicesFunc(zone)
svcs, headlessSvcs := e.externalServicesFunc(zone, e.headless)
srvSeen := make(map[string]struct{})
for i := range svcs {
name := msg.Domain(svcs[i].Key)
if svcs[i].TargetStrip == 0 {
// Add Service A/AAAA records
s := request.Request{Req: &dns.Msg{Question: []dns.Question{{Name: name}}}}
@@ -81,6 +85,55 @@ func (e *External) Transfer(zone string, serial uint32) (<-chan []dns.RR, error)
}
}
}
for key, svcs := range headlessSvcs {
// we have to strip the leading key because it's either port.protocol or endpoint
name := msg.Domain(key[:strings.LastIndex(key, "/")])
switchKey := key[strings.LastIndex(key, "/")+1:]
switch switchKey {
case kubernetes.Endpoint:
// headless.namespace.example.com records
s := request.Request{Req: &dns.Msg{Question: []dns.Question{{Name: name}}}}
as, _ := e.a(ctx, svcs, s)
if len(as) > 0 {
ch <- as
}
aaaas, _ := e.aaaa(ctx, svcs, s)
if len(aaaas) > 0 {
ch <- aaaas
}
// Add bare SRV record, ensuring uniqueness
recs, _ := e.srv(ctx, svcs, s)
ch <- recs
for _, srv := range recs {
ch <- []dns.RR{srv}
}
for i := range svcs {
// endpoint.headless.namespace.example.com record
s := request.Request{Req: &dns.Msg{Question: []dns.Question{{Name: msg.Domain(svcs[i].Key)}}}}
as, _ := e.a(ctx, []msg.Service{svcs[i]}, s)
if len(as) > 0 {
ch <- as
}
aaaas, _ := e.aaaa(ctx, []msg.Service{svcs[i]}, s)
if len(aaaas) > 0 {
ch <- aaaas
}
// Add bare SRV record, ensuring uniqueness
recs, _ := e.srv(ctx, []msg.Service{svcs[i]}, s)
ch <- recs
for _, srv := range recs {
ch <- []dns.RR{srv}
}
}
case kubernetes.PortProtocol:
s := request.Request{Req: &dns.Msg{Question: []dns.Question{{Name: name}}}}
recs, _ := e.srv(ctx, svcs, s)
ch <- recs
}
}
ch <- []dns.RR{soa}
close(ch)
}()

3
plugin/k8s_external/transfer_test.go
View File

@@ -27,6 +27,7 @@ func TestTransferAXFR(t *testing.T) {
k.APIConn = &external{}
e := New()
e.headless = true
e.Zones = []string{"example.com."}
e.externalFunc = k.External
e.externalAddrFunc = externalAddress // internal test function
@@ -64,6 +65,7 @@ func TestTransferAXFR(t *testing.T) {
if ans.Header().Rrtype == dns.TypePTR {
continue
}
expect = append(expect, ans)
}
}
@@ -92,6 +94,7 @@ func TestTransferIXFR(t *testing.T) {
e := New()
e.Zones = []string{"example.com."}
e.headless = true
e.externalFunc = k.External
e.externalAddrFunc = externalAddress // internal test function
e.externalSerialFunc = externalSerial // internal test function