Merge pull request #45148 from rickypai/rpai/use_host_aliases

Automatic merge from submit-queue (batch tested with PRs 45110, 45148)

write HostAliases to hosts file

**What this PR does / why we need it**: using the PodSpec's `HostAliases`, we write entries into the Kubernetes-managed hosts file.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #43632

**Special notes for your reviewer**:
Previous PRs in this series:
- https://github.com/kubernetes/kubernetes/pull/44572 isolates the logic of creating the file and writing the file
- https://github.com/kubernetes/kubernetes/pull/44641 introduces the `HostAliases` field in PodSpec along with validations

**Release note**:
```release-note
PodSpec's `HostAliases` now write entries into the Kubernetes-managed hosts file.
```

@thockin @yujuhong 

Thanks for reviewing!

pkg/kubelet/kubelet_pods.go

@@ -181,7 +181,8 @@ func makeMounts(pod *v1.Pod, podDir string, container *v1.Container, hostName, h
 		})
 	}
 	if mountEtcHostsFile {
-		hostsMount, err := makeHostsMount(podDir, podIP, hostName, hostDomain)
+		hostAliases := pod.Spec.HostAliases
+		hostsMount, err := makeHostsMount(podDir, podIP, hostName, hostDomain, hostAliases)
 		if err != nil {
 			return nil, err
 		}
@@ -192,9 +193,9 @@ func makeMounts(pod *v1.Pod, podDir string, container *v1.Container, hostName, h
 
 // makeHostsMount makes the mountpoint for the hosts file that the containers
 // in a pod are injected with.
-func makeHostsMount(podDir, podIP, hostName, hostDomainName string) (*kubecontainer.Mount, error) {
+func makeHostsMount(podDir, podIP, hostName, hostDomainName string, hostAliases []v1.HostAlias) (*kubecontainer.Mount, error) {
 	hostsFilePath := path.Join(podDir, "etc-hosts")
-	if err := ensureHostsFile(hostsFilePath, podIP, hostName, hostDomainName); err != nil {
+	if err := ensureHostsFile(hostsFilePath, podIP, hostName, hostDomainName, hostAliases); err != nil {
 		return nil, err
 	}
 	return &kubecontainer.Mount{
@@ -208,17 +209,17 @@ func makeHostsMount(podDir, podIP, hostName, hostDomainName string) (*kubecontai
 
 // ensureHostsFile ensures that the given host file has an up-to-date ip, host
 // name, and domain name.
-func ensureHostsFile(fileName, hostIP, hostName, hostDomainName string) error {
+func ensureHostsFile(fileName, hostIP, hostName, hostDomainName string, hostAliases []v1.HostAlias) error {
 	if _, err := os.Stat(fileName); os.IsExist(err) {
 		glog.V(4).Infof("kubernetes-managed etc-hosts file exits. Will not be recreated: %q", fileName)
 		return nil
 	}
-	content := hostsFileContent(hostIP, hostName, hostDomainName)
+	content := hostsFileContent(hostIP, hostName, hostDomainName, hostAliases)
 	return ioutil.WriteFile(fileName, content, 0644)
 }
 
 // hostsFileContent is the content of the managed etc hosts
-func hostsFileContent(hostIP, hostName, hostDomainName string) []byte {
+func hostsFileContent(hostIP, hostName, hostDomainName string, hostAliases []v1.HostAlias) []byte {
 	var buffer bytes.Buffer
 	buffer.WriteString("# Kubernetes-managed hosts file.\n")
 	buffer.WriteString("127.0.0.1\tlocalhost\n")                      // ipv4 localhost
@@ -232,6 +233,12 @@ func hostsFileContent(hostIP, hostName, hostDomainName string) []byte {
 	} else {
 		buffer.WriteString(fmt.Sprintf("%s\t%s\n", hostIP, hostName))
 	}
+	// write each IP/hostname pair as an entry into hosts file
+	for _, hostAlias := range hostAliases {
+		for _, hostname := range hostAlias.Hostnames {
+			buffer.WriteString(fmt.Sprintf("%s\t%s\n", hostAlias.IP, hostname))
+		}
+	}
 	return buffer.Bytes()
 }
 

pkg/kubelet/kubelet_pods_test.go

@@ -119,12 +119,14 @@ func TestHostsFileContent(t *testing.T) {
 		hostIP          string
 		hostName        string
 		hostDomainName  string
+		hostAliases     []v1.HostAlias
 		expectedContent string
 	}{
 		{
 			"123.45.67.89",
 			"podFoo",
 			"",
+			[]v1.HostAlias{},
 			`# Kubernetes-managed hosts file.
 127.0.0.1	localhost
 ::1	localhost ip6-localhost ip6-loopback
@@ -139,6 +141,7 @@ fe00::2	ip6-allrouters
 			"203.0.113.1",
 			"podFoo",
 			"domainFoo",
+			[]v1.HostAlias{},
 			`# Kubernetes-managed hosts file.
 127.0.0.1	localhost
 ::1	localhost ip6-localhost ip6-loopback
@@ -147,12 +150,56 @@ fe00::0	ip6-mcastprefix
 fe00::1	ip6-allnodes
 fe00::2	ip6-allrouters
 203.0.113.1	podFoo.domainFoo	podFoo
+`,
+		},
+		{
+			"203.0.113.1",
+			"podFoo",
+			"domainFoo",
+			[]v1.HostAlias{
+				{IP: "123.45.67.89", Hostnames: []string{"foo", "bar", "baz"}},
+			},
+			`# Kubernetes-managed hosts file.
+127.0.0.1	localhost
+::1	localhost ip6-localhost ip6-loopback
+fe00::0	ip6-localnet
+fe00::0	ip6-mcastprefix
+fe00::1	ip6-allnodes
+fe00::2	ip6-allrouters
+203.0.113.1	podFoo.domainFoo	podFoo
+123.45.67.89	foo
+123.45.67.89	bar
+123.45.67.89	baz
+`,
+		},
+		{
+			"203.0.113.1",
+			"podFoo",
+			"domainFoo",
+			[]v1.HostAlias{
+				{IP: "123.45.67.89", Hostnames: []string{"foo", "bar", "baz"}},
+				{IP: "456.78.90.123", Hostnames: []string{"park", "doo", "boo"}},
+			},
+			`# Kubernetes-managed hosts file.
+127.0.0.1	localhost
+::1	localhost ip6-localhost ip6-loopback
+fe00::0	ip6-localnet
+fe00::0	ip6-mcastprefix
+fe00::1	ip6-allnodes
+fe00::2	ip6-allrouters
+203.0.113.1	podFoo.domainFoo	podFoo
+123.45.67.89	foo
+123.45.67.89	bar
+123.45.67.89	baz
+456.78.90.123	park
+456.78.90.123	doo
+456.78.90.123	boo
 `,
 		},
 	}
 
 	for _, testCase := range testCases {
-		actualContent := string(hostsFileContent(testCase.hostIP, testCase.hostName, testCase.hostDomainName))
+		actualContent := string(hostsFileContent(testCase.hostIP, testCase.hostName, testCase.hostDomainName, testCase.hostAliases))
 		assert.Equal(t, testCase.expectedContent, actualContent, "hosts file content not expected")
 	}
 }