Explorer example shows what environment k8s runs your container in.

examples/explorer/Dockerfile

+# 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.
+
+FROM scratch
+MAINTAINER Daniel Smith <dbsmith@google.com>
+ADD explorer explorer
+ADD README.md README.md
+EXPOSE 8080
+ENTRYPOINT ["/explorer"]

examples/explorer/Makefile

+all: push
+
+# Keep this one version ahead, so no one accidentally blows away the latest published version.
+TAG = 1.1
+
+explorer: explorer.go
+	CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -ldflags '-w' ./explorer.go
+
+container: explorer
+	docker build -t gcr.io/google_containers/explorer:$(TAG) .
+
+push: container
+	gcloud preview docker push gcr.io/google_containers/explorer:$(TAG)
+
+clean:
+	rm -f explorer

examples/explorer/README.md

+### explorer
+
+Explorer is a little container for examining the runtime environment kubernetes produces for your pods.
+
+The intended use is to substitute gcr.io/google_containers/explorer for your intended container, and then visit it via the proxy.
+
+Currently, you can look at:
+ * The environment variables to make sure kubernetes is doing what you expect.
+ * The filesystem to make sure the mounted volumes and files are also what you expect.
+ * Perform DNS lookups, to see how DNS works.
+
+`pod.json` is supplied as an example. You can control the port it serves on with the -port flag.
+
+Example from command line (the DNS lookup looks better from a web browser):
+```
+$ alias kctl=../../../cluster/kubectl.sh
+$ kctl create -f pod.json
+$ kctl proxy &
+Starting to serve on localhost:8001
+
+$ curl localhost:8001/api/v1beta3/proxy/namespaces/default/pods/explorer:8080/vars/
+PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+HOSTNAME=explorer
+KIBANA_LOGGING_PORT_5601_TCP_PORT=5601
+KUBERNETES_SERVICE_HOST=10.0.0.2
+MONITORING_GRAFANA_PORT_80_TCP_PROTO=tcp
+MONITORING_INFLUXDB_UI_PORT_80_TCP_PROTO=tcp
+KIBANA_LOGGING_SERVICE_PORT=5601
+MONITORING_HEAPSTER_PORT_80_TCP_PORT=80
+MONITORING_INFLUXDB_UI_PORT_80_TCP_PORT=80
+KIBANA_LOGGING_SERVICE_HOST=10.0.204.206
+KIBANA_LOGGING_PORT_5601_TCP=tcp://10.0.204.206:5601
+KUBERNETES_PORT=tcp://10.0.0.2:443
+MONITORING_INFLUXDB_PORT=tcp://10.0.2.30:80
+MONITORING_INFLUXDB_PORT_80_TCP_PROTO=tcp
+MONITORING_INFLUXDB_UI_PORT=tcp://10.0.36.78:80
+KUBE_DNS_PORT_53_UDP=udp://10.0.0.10:53
+MONITORING_INFLUXDB_SERVICE_HOST=10.0.2.30
+ELASTICSEARCH_LOGGING_PORT=tcp://10.0.48.200:9200
+ELASTICSEARCH_LOGGING_PORT_9200_TCP_PORT=9200
+KUBERNETES_PORT_443_TCP=tcp://10.0.0.2:443
+ELASTICSEARCH_LOGGING_PORT_9200_TCP_PROTO=tcp
+KIBANA_LOGGING_PORT_5601_TCP_ADDR=10.0.204.206
+KUBE_DNS_PORT_53_UDP_ADDR=10.0.0.10
+MONITORING_HEAPSTER_PORT_80_TCP_PROTO=tcp
+MONITORING_INFLUXDB_PORT_80_TCP_ADDR=10.0.2.30
+KIBANA_LOGGING_PORT=tcp://10.0.204.206:5601
+MONITORING_GRAFANA_SERVICE_PORT=80
+MONITORING_HEAPSTER_SERVICE_PORT=80
+MONITORING_HEAPSTER_PORT_80_TCP=tcp://10.0.150.238:80
+ELASTICSEARCH_LOGGING_PORT_9200_TCP=tcp://10.0.48.200:9200
+ELASTICSEARCH_LOGGING_PORT_9200_TCP_ADDR=10.0.48.200
+MONITORING_GRAFANA_PORT_80_TCP_PORT=80
+MONITORING_HEAPSTER_PORT=tcp://10.0.150.238:80
+MONITORING_INFLUXDB_PORT_80_TCP=tcp://10.0.2.30:80
+KUBE_DNS_SERVICE_PORT=53
+KUBE_DNS_PORT_53_UDP_PORT=53
+MONITORING_GRAFANA_PORT_80_TCP_ADDR=10.0.100.174
+MONITORING_INFLUXDB_UI_SERVICE_HOST=10.0.36.78
+KIBANA_LOGGING_PORT_5601_TCP_PROTO=tcp
+MONITORING_GRAFANA_PORT=tcp://10.0.100.174:80
+MONITORING_INFLUXDB_UI_PORT_80_TCP_ADDR=10.0.36.78
+KUBE_DNS_SERVICE_HOST=10.0.0.10
+KUBERNETES_PORT_443_TCP_PORT=443
+MONITORING_HEAPSTER_PORT_80_TCP_ADDR=10.0.150.238
+MONITORING_INFLUXDB_UI_SERVICE_PORT=80
+KUBE_DNS_PORT=udp://10.0.0.10:53
+ELASTICSEARCH_LOGGING_SERVICE_HOST=10.0.48.200
+KUBERNETES_SERVICE_PORT=443
+MONITORING_HEAPSTER_SERVICE_HOST=10.0.150.238
+MONITORING_INFLUXDB_SERVICE_PORT=80
+MONITORING_INFLUXDB_PORT_80_TCP_PORT=80
+KUBE_DNS_PORT_53_UDP_PROTO=udp
+MONITORING_GRAFANA_PORT_80_TCP=tcp://10.0.100.174:80
+ELASTICSEARCH_LOGGING_SERVICE_PORT=9200
+MONITORING_GRAFANA_SERVICE_HOST=10.0.100.174
+MONITORING_INFLUXDB_UI_PORT_80_TCP=tcp://10.0.36.78:80
+KUBERNETES_PORT_443_TCP_PROTO=tcp
+KUBERNETES_PORT_443_TCP_ADDR=10.0.0.2
+HOME=/
+
+$ curl localhost:8001/api/v1beta3/proxy/namespaces/default/pods/explorer:8080/fs/
+mount/
+var/
+.dockerenv
+etc/
+dev/
+proc/
+.dockerinit
+sys/
+README.md
+explorer
+
+$ curl localhost:8001/api/v1beta3/proxy/namespaces/default/pods/explorer:8080/dns?q=elasticsearch-logging
+<html><head></head><body>
+<form action="/api/v1beta3/proxy/namespaces/default/pods/explorer:8080/dns">
+<input name="q" type="text" value="elasticsearch-logging"/>
+<button type="submit">Lookup</button>
+</form>
+<br/><br/><pre>LookupNS(elasticsearch-logging):
+Result: ([]*net.NS)<nil>
+Error: &lt;*&gt;lookup elasticsearch-logging: no such host
+
+LookupTXT(elasticsearch-logging):
+Result: ([]string)<nil>
+Error: &lt;*&gt;lookup elasticsearch-logging: no such host
+
+LookupSRV(&#34;&#34;, &#34;&#34;, elasticsearch-logging):
+cname: elasticsearch-logging.default.cluster.local.
+Result: ([]*net.SRV)[&lt;*&gt;{Target:(string)elasticsearch-logging.default.cluster.local. Port:(uint16)9200 Priority:(uint16)10 Weight:(uint16)100}]
+Error: <nil>
+
+LookupHost(elasticsearch-logging):
+Result: ([]string)[10.0.60.245]
+Error: <nil>
+
+LookupIP(elasticsearch-logging):
+Result: ([]net.IP)[10.0.60.245]
+Error: <nil>
+
+LookupMX(elasticsearch-logging):
+Result: ([]*net.MX)<nil>
+Error: &lt;*&gt;lookup elasticsearch-logging: no such host
+
+</nil></nil></nil></nil></nil></nil></pre>
+
+</body></html>
+```

examples/explorer/explorer.go

+/*
+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.
+*/
+
+// A tiny web server for viewing the environment kubernetes creates for your
+// containers. It exposes the filesystem and environment variables via http
+// server.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"os"
+
+	"github.com/davecgh/go-spew/spew"
+)
+
+var (
+	port = flag.Int("port", 8080, "Port number to serve at.")
+)
+
+func main() {
+	flag.Parse()
+	hostname, err := os.Hostname()
+	if err != nil {
+		log.Fatalf("Error getting hostname: %v", err)
+	}
+
+	links := []struct {
+		link, desc string
+	}{
+		{"/fs/", "Complete file system as seen by this container."},
+		{"/vars/", "Environment variables as seen by this container."},
+		{"/hostname/", "Hostname as seen by this container."},
+		{"/dns?q=google.com", "Explore DNS records seen by this container."},
+		{"/quit", "Cause this container to exit."},
+	}
+
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, "<b> Kubernetes environment explorer </b><br/><br/>")
+		for _, v := range links {
+			fmt.Fprintf(w, `<a href="%v">%v: %v</a><br/>`, v.link, v.link, v.desc)
+		}
+	})
+
+	http.Handle("/fs/", http.StripPrefix("/fs/", http.FileServer(http.Dir("/"))))
+	http.HandleFunc("/vars/", func(w http.ResponseWriter, r *http.Request) {
+		for _, v := range os.Environ() {
+			fmt.Fprintf(w, "%v\n", v)
+		}
+	})
+	http.HandleFunc("/hostname/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, hostname)
+	})
+	http.HandleFunc("/quit", func(w http.ResponseWriter, r *http.Request) {
+		os.Exit(0)
+	})
+	http.HandleFunc("/dns", dns)
+
+	go log.Fatal(http.ListenAndServe(fmt.Sprintf("0.0.0.0:%d", *port), nil))
+
+	select {}
+}
+
+func dns(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query().Get("q")
+	// Note that the below is NOT safe from input attacks, but that's OK
+	// because this is just for debugging.
+	fmt.Fprintf(w, `<html><body>
+<form action="/dns">
+<input name="q" type="text" value="%v"></input>
+<button type="submit">Lookup</button>
+</form>
+<br/><br/><pre>`, q)
+	{
+		res, err := net.LookupNS(q)
+		spew.Fprintf(w, "LookupNS(%v):\nResult: %#v\nError: %v\n\n", q, res, err)
+	}
+	{
+		res, err := net.LookupTXT(q)
+		spew.Fprintf(w, "LookupTXT(%v):\nResult: %#v\nError: %v\n\n", q, res, err)
+	}
+	{
+		cname, res, err := net.LookupSRV("", "", q)
+		spew.Fprintf(w, `LookupSRV("", "", %v):
+cname: %v
+Result: %#v
+Error: %v
+
+`, q, cname, res, err)
+	}
+	{
+		res, err := net.LookupHost(q)
+		spew.Fprintf(w, "LookupHost(%v):\nResult: %#v\nError: %v\n\n", q, res, err)
+	}
+	{
+		res, err := net.LookupIP(q)
+		spew.Fprintf(w, "LookupIP(%v):\nResult: %#v\nError: %v\n\n", q, res, err)
+	}
+	{
+		res, err := net.LookupMX(q)
+		spew.Fprintf(w, "LookupMX(%v):\nResult: %#v\nError: %v\n\n", q, res, err)
+	}
+	fmt.Fprintf(w, `</pre>
+</body>
+</html>`)
+}

examples/explorer/pod.json

+{
+  "kind": "Pod",
+  "apiVersion": "v1beta3",
+  "metadata": {
+    "name": "explorer"
+  },
+  "spec": {
+    "containers": [
+      {
+        "name": "explorer",
+        "image": "gcr.io/google_containers/explorer:1.0",
+        "args": [
+          "-port=8080"
+        ],
+        "ports": [
+          {
+            "containerPort": 8080,
+            "protocol": "TCP"
+          }
+        ],
+        "volumeMounts": [
+          {
+            "name": "test-volume",
+            "mountPath": "/mount/test-volume"
+          }
+        ]
+      }
+    ],
+    "volumes": [
+      {
+        "name": "test-volume",
+        "VolumeSorce": {
+          "EmptyDir": {}
+        }
+      }
+    ]
+  }
+}