Initial support for multi kubernetes clusters for k8s nodes

Change-Id: I6ca132898f8e157e0583de38a637fdc135f21d6f
(cherry picked from commit e2a04cedde73618ef24575e70cb221e03854de1d)
diff --git a/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sExternalNetwork.java b/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sExternalNetwork.java
new file mode 100644
index 0000000..3462ad0
--- /dev/null
+++ b/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sExternalNetwork.java
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2020-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.k8snode.api;
+
+import org.onlab.packet.IpAddress;
+import org.onlab.packet.MacAddress;
+
+/**
+ * Representation of an external network.
+ */
+public interface K8sExternalNetwork {
+
+    /**
+     * Returns the external bridge's IP address.
+     *
+     * @return IP address; null if the IP address does not exist
+     */
+    IpAddress extBridgeIp();
+
+    /**
+     * Returns the external gateway IP address.
+     *
+     * @return IP address; null if the IP address does not exist
+     */
+    IpAddress extGatewayIp();
+
+    /**
+     * Returns the external gateway MAC address.
+     *
+     * @return MAC address; null if the MAC address does not exist
+     */
+    MacAddress extGatewayMac();
+
+    /**
+     * Builder of new network entity.
+     */
+    interface Builder {
+
+        /**
+         * Builds an immutable kubernetes external network instance.
+         *
+         * @return kubernetes external network
+         */
+        K8sExternalNetwork build();
+
+        /**
+         * Returns kubernetes node builder with supplied external bridge IP.
+         *
+         * @param extBridgeIp external bridge IP
+         * @return kubernetes node builder
+         */
+        Builder extBridgeIp(IpAddress extBridgeIp);
+
+        /**
+         * Returns kubernetes node builder with supplied gateway IP.
+         *
+         * @param extGatewayIp external gateway IP
+         * @return kubernetes node builder
+         */
+        Builder extGatewayIp(IpAddress extGatewayIp);
+
+        /**
+         * Returns kubernetes node builder with supplied external gateway MAC.
+         *
+         * @param extGatewayMac external gateway MAC address
+         * @return kubernetes node builder
+         */
+        Builder extGatewayMac(MacAddress extGatewayMac);
+    }
+}