e2e: Add test to pd that disk contents are preserved

Issue #11012 reported that disk contents may be lost (sometimes).

We should have an e2e test to verify this is not happening.

(If it is happening, we should then fix it!)

test/e2e/pd.go

@@ -18,10 +18,12 @@ package e2e
 
 import (
 	"fmt"
+	math_rand "math/rand"
 	"os/exec"
 	"strings"
 	"time"
 
+	"bytes"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api/latest"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/client"
@@ -86,6 +88,12 @@ var _ = Describe("Pod Disks", func() {
 
 		expectNoError(waitForPodRunning(c, host0Pod.Name))
 
+		testFile := "/testpd/tracker"
+		testFileContents := fmt.Sprintf("%v", math_rand.Int())
+
+		expectNoError(writeFileOnPod(c, host0Pod.Name, testFile, testFileContents))
+		Logf("Wrote value: %v", testFileContents)
+
 		By("deleting host0Pod")
 		expectNoError(podClient.Delete(host0Pod.Name, nil), "Failed to delete host0Pod")
 
@@ -95,6 +103,12 @@ var _ = Describe("Pod Disks", func() {
 
 		expectNoError(waitForPodRunning(c, host1Pod.Name))
 
+		v, err := readFileOnPod(c, host1Pod.Name, testFile)
+		expectNoError(err)
+		Logf("Read value: %v", v)
+
+		Expect(strings.TrimSpace(v)).To(Equal(strings.TrimSpace(testFileContents)))
+
 		By("deleting host1Pod")
 		expectNoError(podClient.Delete(host1Pod.Name, nil), "Failed to delete host1Pod")
 
@@ -173,6 +187,48 @@ var _ = Describe("Pod Disks", func() {
 	})
 })
 
+func kubectlExec(namespace string, podName string, args ...string) ([]byte, []byte, error) {
+	var stdout, stderr bytes.Buffer
+	cmdArgs := []string{"exec", fmt.Sprintf("--namespace=%v", namespace), podName}
+	cmdArgs = append(cmdArgs, args...)
+
+	cmd := kubectlCmd(cmdArgs...)
+	cmd.Stdout, cmd.Stderr = &stdout, &stderr
+
+	Logf("Running '%s %s'", cmd.Path, strings.Join(cmd.Args, " "))
+	err := cmd.Run()
+	return stdout.Bytes(), stderr.Bytes(), err
+}
+
+// Write a file using kubectl exec echo <contents> > <path>
+// Because of the primitive technique we're using here, we only allow ASCII alphanumeric characters
+func writeFileOnPod(c *client.Client, podName string, path string, contents string) error {
+	By("writing a file in the container")
+	allowedCharacters := "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	for _, c := range contents {
+		if !strings.ContainsRune(allowedCharacters, c) {
+			return fmt.Errorf("Unsupported character in string to write: %v", c)
+		}
+	}
+	command := fmt.Sprintf("echo '%s' > '%s'", contents, path)
+	stdout, stderr, err := kubectlExec(api.NamespaceDefault, podName, "--", "/bin/sh", "-c", command)
+	if err != nil {
+		Logf("error running kubectl exec to write file: %v\nstdout=%v\nstderr=%v)", err, string(stdout), string(stderr))
+	}
+	return err
+}
+
+// Read a file using kubectl exec cat <path>
+func readFileOnPod(c *client.Client, podName string, path string) (string, error) {
+	By("reading a file in the container")
+
+	stdout, stderr, err := kubectlExec(api.NamespaceDefault, podName, "--", "cat", path)
+	if err != nil {
+		Logf("error running kubectl exec to read file: %v\nstdout=%v\nstderr=%v)", err, string(stdout), string(stderr))
+	}
+	return string(stdout), err
+}
+
 func createPD() (string, error) {
 	if testContext.Provider == "gce" || testContext.Provider == "gke" {
 		pdName := fmt.Sprintf("%s-%s", testContext.prefix, string(util.NewUUID()))
@@ -244,8 +300,9 @@ func testPDPod(diskName, targetHost string, readOnly bool) *api.Pod {
 		Spec: api.PodSpec{
 			Containers: []api.Container{
 				{
-					Name:  "testpd",
-					Image: "gcr.io/google_containers/pause",
+					Name:    "testpd",
+					Image:   "gcr.io/google_containers/busybox",
+					Command: []string{"sleep", "600"},
 					VolumeMounts: []api.VolumeMount{
 						{
 							Name:      "testpd",