Error out when multiple https endpoints are specified. (#2438)

This fix will error out when multiple https endpoints are specified,
as additional work is needed to support beyond http.

This fix fixes 1464.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/kubernetes/README.md

@@ -52,8 +52,9 @@ kubernetes [ZONES...] {
 * `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.
+   `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/setup.go

@@ -196,6 +196,15 @@ func ParseStanza(c *caddy.Controller) (*Kubernetes, error) {
 			args := c.RemainingArgs()
 			if len(args) > 0 {
 				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])
+						}
+					}
+				}
 				continue
 			}
 			return nil, c.ArgErr()

plugin/kubernetes/setup_test.go

@@ -439,6 +439,20 @@ kubernetes cluster.local`,
 			fall.Zero,
 			nil,
 		},
+		{
+			`kubernetes coredns.local {
+    endpoint http://localhost:9090 https://localhost:9091
+}`,
+			true,
+			"multiple endpoints can only accept http",
+			-1,
+			-1,
+			defaultResyncPeriod,
+			"",
+			podModeDisabled,
+			fall.Zero,
+			nil,
+		},
 	}
 
 	for i, test := range tests {