Deprecate multiple endpoints for out-of-cluster k8s api (#2454)

This fix deprecates endpoints for out-of-cluster k8s api,
The Corefile still takes multiple endpoints though only
the first one is used. A warning is shown if there are
multiple endpoints.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/kubernetes/README.md

@@ -32,7 +32,7 @@ all the zones the plugin should be authoritative for.
 ```
 kubernetes [ZONES...] {
     resyncperiod DURATION
-    endpoint URL [URL...]
+    endpoint URL
     tls CERT KEY CACERT
     kubeconfig KUBECONFIG CONTEXT
     namespaces NAMESPACE...
@@ -51,10 +51,6 @@ kubernetes [ZONES...] {
 * `resyncperiod` specifies the Kubernetes data API **DURATION** period.
 * `endpoint` specifies the **URL** for a remote k8s API endpoint.
    If omitted, it will connect to k8s in-cluster using the cluster service account.
-   Multiple k8s API endpoints could be specified:
-   `endpoint http://k8s-endpoint1:8080 http://k8s-endpoint2:8080`.
-   CoreDNS will automatically perform a healthcheck and proxy to the healthy k8s API endpoint.
-   Note that only http is supported when more than one k8s API endpoints are specified at the moment.
 * `tls` **CERT** **KEY** **CACERT** are the TLS cert, key and the CA cert file names for remote k8s connection.
    This option is ignored if connecting in-cluster (i.e. endpoint is not specified).
 * `kubeconfig` **KUBECONFIG** **CONTEXT** authenticates the connection to a remote k8s cluster using a kubeconfig file. It supports TLS, username and password, or token-based authentication. This option is ignored if connecting in-cluster (i.e., the endpoint is not specified).

plugin/kubernetes/kubernetes.go

@@ -6,15 +6,12 @@ import (
 	"fmt"
 	"net"
 	"strings"
-	"sync/atomic"
-	"time"
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/etcd/msg"
 	"github.com/coredns/coredns/plugin/kubernetes/object"
 	"github.com/coredns/coredns/plugin/pkg/dnsutil"
 	"github.com/coredns/coredns/plugin/pkg/fall"
-	"github.com/coredns/coredns/plugin/pkg/healthcheck"
 	"github.com/coredns/coredns/plugin/pkg/upstream"
 	"github.com/coredns/coredns/request"
 
@@ -174,50 +171,8 @@ func (k *Kubernetes) getClientConfig() (*rest.Config, error) {
 	}
 
 	// Connect to API from out of cluster
-	endpoint := k.APIServerList[0]
-	if len(k.APIServerList) > 1 {
-		// Use a random port for api proxy, will get the value later through listener.Addr()
-		listener, err := net.Listen("tcp", "127.0.0.1:0")
-		if err != nil {
-			return nil, fmt.Errorf("failed to create kubernetes api proxy: %v", err)
-		}
-		k.APIProxy = &apiProxy{
-			listener: listener,
-			handler: proxyHandler{
-				HealthCheck: healthcheck.HealthCheck{
-					FailTimeout: 3 * time.Second,
-					MaxFails:    1,
-					Path:        "/",
-					Interval:    5 * time.Second,
-				},
-			},
-		}
-		k.APIProxy.handler.Hosts = make([]*healthcheck.UpstreamHost, len(k.APIServerList))
-		for i, entry := range k.APIServerList {
-
-			uh := &healthcheck.UpstreamHost{
-				Name: strings.TrimPrefix(entry, "http://"),
-
-				CheckDown: func(upstream *proxyHandler) healthcheck.UpstreamHostDownFunc {
-					return func(uh *healthcheck.UpstreamHost) bool {
-
-						fails := atomic.LoadInt32(&uh.Fails)
-						if fails >= upstream.MaxFails && upstream.MaxFails != 0 {
-							return true
-						}
-						return false
-					}
-				}(&k.APIProxy.handler),
-			}
-
-			k.APIProxy.handler.Hosts[i] = uh
-		}
-		k.APIProxy.Handler = &k.APIProxy.handler
-
-		// Find the random port used for api proxy
-		endpoint = fmt.Sprintf("http://%s", listener.Addr())
-	}
-	clusterinfo.Server = endpoint
+	// Only the first one is used. We will deprecated multiple endpoints later.
+	clusterinfo.Server = k.APIServerList[0]
 
 	if len(k.APICertAuth) > 0 {
 		clusterinfo.CertificateAuthority = k.APICertAuth

plugin/kubernetes/setup.go

@@ -195,15 +195,11 @@ func ParseStanza(c *caddy.Controller) (*Kubernetes, error) {
 		case "endpoint":
 			args := c.RemainingArgs()
 			if len(args) > 0 {
+				// Multiple endoints are deprecated but still could be specified,
+				// only the first one be used, though
 				k8s.APIServerList = args
 				if len(args) > 1 {
-					// If multiple endoints specified, then only http allowed
-					for i := range args {
-						parts := strings.SplitN(args[i], "://", 2)
-						if len(parts) == 2 && parts[0] != "http" {
-							return nil, fmt.Errorf("multiple endpoints can only accept http, found: %v", args[i])
-						}
-					}
+					log.Warningf("Multiple endpoints have been deprecated, only the first specified endpoint '%s' is used", args[0])
 				}
 				continue
 			}

plugin/kubernetes/setup_test.go

@@ -394,19 +394,6 @@ kubernetes cluster.local`,
 			podModeDisabled,
 			fall.Zero,
 		},
-		{
-			`kubernetes coredns.local {
-    endpoint http://localhost:9090 https://localhost:9091
-}`,
-			true,
-			"multiple endpoints can only accept http",
-			-1,
-			-1,
-			defaultResyncPeriod,
-			"",
-			podModeDisabled,
-			fall.Zero,
-		},
 	}
 
 	for i, test := range tests {