Add Environment Guide example.

This example shows a simple two tier setup in Kubernetes, and
simply prints the environment information that each pod sees.
Querying the service multiple times will show services at work
load balancing requests.

examples/environment-guide/README.md

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+Environment Guide Example
+=========================
+This example demonstrates running pods, replication controllers, and
+services. It shows two types of pods: frontend and backend, with
+services on top of both. Accessing the frontend pod will return
+environment information about itself, and a backend pod that it has
+accessed through the service. The goal is to illuminate the
+environment metadata available to running containers inside the
+Kubernetes cluster. The documentation for the kubernetes environment
+is [here](/docs/container-environment.md).
+
+![Diagram](diagram.png)
+
+Prerequisites
+-------------
+This example assumes that you have a Kubernetes cluster installed and
+running, and that you have installed the `kubectl` command line tool
+somewhere in your path.  Please see the [getting
+started](/docs/getting-started-guides) for installation instructions
+for your platform.
+
+Optional: Build your own containers
+-----------------------------------
+The code for the containers is under
+[containers/](containers)
+
+Get everything running
+----------------------
+
+    kubectl create -f ./backend-rc.yaml
+    kubectl create -f ./backend-srv.yaml
+    kubectl create -f ./show-rc.yaml
+    kubectl create -f ./show-srv.yaml
+
+Query the service
+-----------------
+Use `kubectl describe service show-srv` to determine the public IP of
+your service.
+
+> Note: If your platform does not support external load balancers,
+  you'll need to open the proper port and direct traffic to the
+  internal IP shown for the frontend service with the above command
+
+Run `curl <public ip>:80` to query the service. You should get
+something like this back:
+
+```
+Pod Name: show-rc-xxu6i
+Pod Namespace: default
+USER_VAR: important information
+
+Kubenertes environment variables
+BACKEND_SRV_SERVICE_HOST = 10.147.252.185
+BACKEND_SRV_SERVICE_PORT = 5000
+KUBERNETES_RO_SERVICE_HOST = 10.147.240.1
+KUBERNETES_RO_SERVICE_PORT = 80
+KUBERNETES_SERVICE_HOST = 10.147.240.2
+KUBERNETES_SERVICE_PORT = 443
+KUBE_DNS_SERVICE_HOST = 10.147.240.10
+KUBE_DNS_SERVICE_PORT = 53
+
+Found backend ip: 10.147.252.185 port: 5000
+Response from backend
+Backend Container
+Backend Pod Name: backend-rc-6qiya
+Backend Namespace: default
+```
+
+First the frontend pod's information is printed. The pod name and
+[namespace](/docs/design/namespaces.md) are retreived from the
+[Downward API](/docs/downward_api.md). Next, `USER_VAR` is the name of
+an environment variable set in the [pod
+definition](show-rc.yaml). Then, the dynamic kubernetes environment
+variables are scanned and printed. These are used to find the backend
+service, named `backend-srv`. Finally, the frontend pod queries the
+backend service and prints the information returned. Again the backend
+pod returns its own pod name and namespace.
+
+Try running the `curl` command a few times, and notice what
+changes. Ex: `watch -n 1 curl -s <ip>` Firstly, the frontend service
+is directing your request to different frontend pods each time. The
+frontend pods are always contacting the backend through the backend
+service. This results in a different backend pod servicing each
+request as well.
+
+Cleanup
+-------
+    kubectl delete rc,service -l type=show-type
+    kubectl delete rc,service -l type=backend-type
+
+
+[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/examples/environment-guide/README.md?pixel)]()

examples/environment-guide/backend-rc.yaml

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+---
+apiVersion: v1
+kind: ReplicationController
+metadata:
+  name: backend-rc
+  labels:
+    type: backend-type
+spec:
+  replicas: 3
+  template:
+    metadata:
+      labels:
+        type: backend-type
+    spec:
+      containers:
+      - name: backend-container
+        image: gcr.io/google-samples/env-backend:1.1
+        imagePullPolicy: Always
+        ports:
+        - containerPort: 5000
+          protocol: TCP
+        env:
+        - name: POD_NAME
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.name
+        - name: POD_NAMESPACE
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.namespace

examples/environment-guide/backend-srv.yaml

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+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: backend-srv
+  labels:
+    type: backend-type
+spec:
+  ports:
+  - port: 5000
+    protocol: TCP
+  selector:
+    type: backend-type

examples/environment-guide/containers/README.md

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+Building
+--------
+For each container, the build steps are the same. The examples below
+are for the `show` container. Replace `show` with `backend` for the
+backend container.
+
+GCR
+---
+    docker build -t gcr.io/<project-name>/show .
+    gcloud preview docker push gcr.io/<project-name>/show
+
+Docker Hub
+----------
+    docker build -t <username>/show .
+    docker push <username>/show
+
+Change Pod Definitions
+----------------------
+Edit both `show-rc.yaml` and `backend-rc.yaml` and replace the
+specified `image:` with the one that you built.
+
+
+[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/examples/environment-guide/containers/README.md?pixel)]()

examples/environment-guide/containers/backend/Dockerfile

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+FROM golang:onbuild
+EXPOSE 8080

examples/environment-guide/containers/backend/backend.go

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+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+)
+
+func printInfo(resp http.ResponseWriter, req *http.Request) {
+	name := os.Getenv("POD_NAME")
+	namespace := os.Getenv("POD_NAMESPACE")
+	fmt.Fprintf(resp, "Backend Container\n")
+	fmt.Fprintf(resp, "Backend Pod Name: %v\n", name)
+	fmt.Fprintf(resp, "Backend Namespace: %v\n", namespace)
+}
+
+func main() {
+	http.HandleFunc("/", printInfo)
+	log.Fatal(http.ListenAndServe(":5000", nil))
+}

examples/environment-guide/containers/show/Dockerfile

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+FROM golang:onbuild
+EXPOSE 8080

examples/environment-guide/containers/show/show.go

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+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"sort"
+	"strings"
+)
+
+func getKubeEnv() (map[string]string, error) {
+	environS := os.Environ()
+	environ := make(map[string]string)
+	for _, val := range environS {
+		split := strings.Split(val, "=")
+		if len(split) != 2 {
+			return environ, fmt.Errorf("Some weird env vars")
+		}
+		environ[split[0]] = split[1]
+	}
+	for key := range environ {
+		if !(strings.HasSuffix(key, "_SERVICE_HOST") ||
+			strings.HasSuffix(key, "_SERVICE_PORT")) {
+			delete(environ, key)
+		}
+	}
+	return environ, nil
+}
+
+func printInfo(resp http.ResponseWriter, req *http.Request) {
+	kubeVars, err := getKubeEnv()
+	if err != nil {
+		http.Error(resp, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	backendHost := os.Getenv("BACKEND_SRV_SERVICE_HOST")
+	backendPort := os.Getenv("BACKEND_SRV_SERVICE_PORT")
+	backendRsp, backendErr := http.Get(fmt.Sprintf(
+		"http://%v:%v/",
+		backendHost,
+		backendPort))
+	if backendErr == nil {
+		defer backendRsp.Body.Close()
+	}
+
+	name := os.Getenv("POD_NAME")
+	namespace := os.Getenv("POD_NAMESPACE")
+	fmt.Fprintf(resp, "Pod Name: %v \n", name)
+	fmt.Fprintf(resp, "Pod Namespace: %v \n", namespace)
+
+	envvar := os.Getenv("USER_VAR")
+	fmt.Fprintf(resp, "USER_VAR: %v \n", envvar)
+
+	fmt.Fprintf(resp, "\nKubenertes environment variables\n")
+	var keys []string
+	for key := range kubeVars {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		fmt.Fprintf(resp, "%v = %v \n", key, kubeVars[key])
+	}
+
+	fmt.Fprintf(resp, "\nFound backend ip: %v port: %v\n", backendHost, backendPort)
+	if backendErr == nil {
+		fmt.Fprintf(resp, "Response from backend\n")
+		io.Copy(resp, backendRsp.Body)
+	} else {
+		fmt.Fprintf(resp, "Error from backend: %v", backendErr.Error())
+	}
+}
+
+func main() {
+	http.HandleFunc("/", printInfo)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}

examples/environment-guide/show-rc.yaml

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+---
+apiVersion: v1
+kind: ReplicationController
+metadata:
+  name: show-rc
+  labels:
+    type: show-type
+spec:
+  replicas: 3
+  template:
+    metadata:
+      labels:
+        type: show-type
+    spec:
+      containers:
+      - name: show-container
+        image: gcr.io/google-samples/env-show:1.1
+        imagePullPolicy: Always
+        ports:
+        - containerPort: 8080
+          protocol: TCP
+        env:
+        - name: USER_VAR
+          value: important information
+        - name: POD_NAME
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.name
+        - name: POD_NAMESPACE
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.namespace

examples/environment-guide/show-srv.yaml

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+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: show-srv
+  labels:
+    type: show-type
+spec:
+  type: LoadBalancer
+  ports:
+  - port: 80
+    protocol: TCP
+    targetPort: 8080
+  selector:
+    type: show-type