Adds Discovery Server and Discovery Client (#886)

Author: Ryan Baxter

README.adoc

@@ -114,6 +114,20 @@ access from a Spring Boot application running as a pod.
 
 This is something that you get for free by adding the following dependency inside your project:
 
+====
+HTTP Based `DiscoveryClient`
+[source,xml]
+----
+<dependency>
+    <groupId>org.springframework.cloud</groupId>
+    <artifactId>spring-cloud-starter-kubernetes-discoveryclient</artifactId>
+</dependency>
+----
+====
+
+NOTE: `spring-cloud-starter-kubernetes-discoveryclient` is designed to be used with the
+<<spring-cloud-kubernetes-discoveryserver, Spring Cloud Kubernetes DiscoveryServer>>.
+
 ====
 Fabric8 Kubernetes Client
 [source,xml]
@@ -1514,6 +1528,219 @@ items:
 ----
 ====
 
+[#spring-cloud-kubernetes-discoveryserver]
+## Spring Cloud Kubernetes Discovery Server
+
+The Spring Cloud Kubernetes Discovery Server provides HTTP endpoints apps can use to gather information
+about services available within a Kubernetes cluster.  The Spring Cloud Kubernetes Discovery Server
+can be used by apps using the `spring-cloud-starter-kubernetes-discoveryclient` to provide data to
+the `DiscoveryClient` implementation provided by that starter.
+
+### Permissions
+The Spring Cloud Discovery server uses
+the Kubernetes API server to get data about Service and Endpoint resrouces so it needs list, watch, and
+get permissions to use those endpoints.  See the below sample Kubernetes deployment YAML for an
+examlpe of how to configure the Service Account on Kubernetes.
+
+
+### Endpoints
+There are three endpoints exposed by the server.
+
+#### `/apps`
+
+A `GET` request sent to `/apps` will return a JSON array of available services.  Each item contains
+the name of the Kubernetes service and service instance information.  Below is a sample response.
+
+====
+[source,json]
+----
+[
+   {
+      "name":"spring-cloud-kubernetes-discoveryserver",
+      "serviceInstances":[
+         {
+            "instanceId":"836a2f25-daee-4af2-a1be-aab9ce2b938f",
+            "serviceId":"spring-cloud-kubernetes-discoveryserver",
+            "host":"10.244.1.6",
+            "port":8761,
+            "uri":"http://10.244.1.6:8761",
+            "secure":false,
+            "metadata":{
+               "app":"spring-cloud-kubernetes-discoveryserver",
+               "kubectl.kubernetes.io/last-applied-configuration":"{\"apiVersion\":\"v1\",\"kind\":\"Service\",\"metadata\":{\"annotations\":{},\"labels\":{\"app\":\"spring-cloud-kubernetes-discoveryserver\"},\"name\":\"spring-cloud-kubernetes-discoveryserver\",\"namespace\":\"default\"},\"spec\":{\"ports\":[{\"name\":\"http\",\"port\":80,\"targetPort\":8761}],\"selector\":{\"app\":\"spring-cloud-kubernetes-discoveryserver\"},\"type\":\"ClusterIP\"}}\n",
+               "http":"8761"
+            },
+            "namespace":"default",
+            "scheme":"http"
+         }
+      ]
+   },
+   {
+      "name":"kubernetes",
+      "serviceInstances":[
+         {
+            "instanceId":"1234",
+            "serviceId":"kubernetes",
+            "host":"172.18.0.3",
+            "port":6443,
+            "uri":"http://172.18.0.3:6443",
+            "secure":false,
+            "metadata":{
+               "provider":"kubernetes",
+               "component":"apiserver",
+               "https":"6443"
+            },
+            "namespace":"default",
+            "scheme":"http"
+         }
+      ]
+   }
+]
+----
+====
+
+#### `/app/{name}`
+
+A `GET` request to `/app/{name}` can be used to get instance data for all instances of a given
+service.  Below is a sample response when a `GET` request is made to `/app/kubernetes`.
+
+====
+[source,json]
+----
+[
+     {
+        "instanceId":"1234",
+        "serviceId":"kubernetes",
+        "host":"172.18.0.3",
+        "port":6443,
+        "uri":"http://172.18.0.3:6443",
+        "secure":false,
+        "metadata":{
+           "provider":"kubernetes",
+           "component":"apiserver",
+           "https":"6443"
+        },
+        "namespace":"default",
+        "scheme":"http"
+     }
+]
+----
+====
+
+#### `/app/{name}/{instanceid}`
+
+A `GET` request made to `/app/{name}/{instanceid}` will return the instance data for a specific
+instance of a given service.  Below is a sample response when a `GET` request is made to `/app/kubernetes/1234`.
+
+====
+[source,json]
+----
+ {
+    "instanceId":"1234",
+    "serviceId":"kubernetes",
+    "host":"172.18.0.3",
+    "port":6443,
+    "uri":"http://172.18.0.3:6443",
+    "secure":false,
+    "metadata":{
+       "provider":"kubernetes",
+       "component":"apiserver",
+       "https":"6443"
+    },
+    "namespace":"default",
+    "scheme":"http"
+ }
+----
+====
+
+### Deployment YAML
+
+An image of the Spring Cloud Discovery Server is hosted on Docker Hub.
+
+Below is a sample deployment YAML you can use to deploy the Kubernetes Configuration Watcher to Kubernetes.
+
+====
+[source,yaml]
+----
+---
+apiVersion: v1
+kind: List
+items:
+  - apiVersion: v1
+    kind: Service
+    metadata:
+      labels:
+        app: spring-cloud-kubernetes-discoveryserver
+      name: spring-cloud-kubernetes-discoveryserver
+    spec:
+      ports:
+        - name: http
+          port: 80
+          targetPort: 8761
+      selector:
+        app: spring-cloud-kubernetes-discoveryserver
+      type: ClusterIP
+  - apiVersion: v1
+    kind: ServiceAccount
+    metadata:
+      labels:
+        app: spring-cloud-kubernetes-discoveryserver
+      name: spring-cloud-kubernetes-discoveryserver
+  - apiVersion: rbac.authorization.k8s.io/v1
+    kind: RoleBinding
+    metadata:
+      labels:
+        app: spring-cloud-kubernetes-discoveryserver
+      name: spring-cloud-kubernetes-discoveryserver:view
+    roleRef:
+      kind: Role
+      apiGroup: rbac.authorization.k8s.io
+      name: namespace-reader
+    subjects:
+      - kind: ServiceAccount
+        name: spring-cloud-kubernetes-discoveryserver
+  - apiVersion: rbac.authorization.k8s.io/v1
+    kind: Role
+    metadata:
+      namespace: default
+      name: namespace-reader
+    rules:
+      - apiGroups: ["", "extensions", "apps"]
+        resources: ["services", "endpoints"]
+        verbs: ["get", "list", "watch"]
+  - apiVersion: apps/v1
+    kind: Deployment
+    metadata:
+      name: spring-cloud-kubernetes-discoveryserver-deployment
+    spec:
+      selector:
+        matchLabels:
+          app: spring-cloud-kubernetes-discoveryserver
+      template:
+        metadata:
+          labels:
+            app: spring-cloud-kubernetes-discoveryserver
+        spec:
+          serviceAccount: spring-cloud-kubernetes-discoveryserver
+          containers:
+          - name: spring-cloud-kubernetes-discoveryserver
+            image: springcloud/spring-cloud-kubernetes-discoveryserver:2.1.0-SNAPSHOT
+            imagePullPolicy: IfNotPresent
+            readinessProbe:
+              httpGet:
+                port: 8761
+                path: /actuator/health/readiness
+            livenessProbe:
+              httpGet:
+                port: 8761
+                path: /actuator/health/liveness
+            ports:
+            - containerPort: 8761
+
+
+----
+====
+
 == Examples
 
 Spring Cloud Kubernetes tries to make it transparent for your applications to consume Kubernetes Native Services by

docs/src/main/asciidoc/discovery-client.adoc

@@ -8,6 +8,20 @@ access from a Spring Boot application running as a pod.
 
 This is something that you get for free by adding the following dependency inside your project:
 
+====
+HTTP Based `DiscoveryClient`
+[source,xml]
+----
+<dependency>
+    <groupId>org.springframework.cloud</groupId>
+    <artifactId>spring-cloud-starter-kubernetes-discoveryclient</artifactId>
+</dependency>
+----
+====
+
+NOTE: `spring-cloud-starter-kubernetes-discoveryclient` is designed to be used with the
+<<spring-cloud-kubernetes-discoveryserver, Spring Cloud Kubernetes DiscoveryServer>>.
+
 ====
 Fabric8 Kubernetes Client
 [source,xml]