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/containers/README.md

@@ -0,0 +1,23 @@
+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

@@ -0,0 +1,2 @@
+FROM golang:onbuild
+EXPOSE 8080

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

@@ -0,0 +1,37 @@
+/*
+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

@@ -0,0 +1,2 @@
+FROM golang:onbuild
+EXPOSE 8080

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

@@ -0,0 +1,95 @@
+/*
+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))
+}