Write HostAliases aliases on same line per host IP

* change HostAliases to put all aliases for an IP
  on the same line in /etc/hosts rather than writing
  one line per IP-alias pair
* having multiple entries in /etc/hosts for the same IP
  causes issues with DNS resolution for some software
* https://unix.stackexchange.com/questions/102660/hosts-file-is-it-incorrect-to-have-the-same-ip-address-on-multiple-lines

pkg/kubelet/kubelet_pods.go

@@ -356,11 +356,9 @@ func hostsEntriesFromHostAliases(hostAliases []v1.HostAlias) []byte {
 	var buffer bytes.Buffer
 	buffer.WriteString("\n")
 	buffer.WriteString("# Entries added by HostAliases.\n")
-	// write each IP/hostname pair as an entry into hosts file
+	// for each IP, write all aliases onto single line in hosts file
 	for _, hostAlias := range hostAliases {
-		for _, hostname := range hostAlias.Hostnames {
-			buffer.WriteString(fmt.Sprintf("%s\t%s\n", hostAlias.IP, hostname))
-		}
+		buffer.WriteString(fmt.Sprintf("%s\t%s\n", hostAlias.IP, strings.Join(hostAlias.Hostnames, "\t")))
 	}
 	return buffer.Bytes()
 }

pkg/kubelet/kubelet_pods_test.go

@@ -183,9 +183,7 @@ fe00::2	ip6-allrouters
 123.45.67.89	some.domain
 
 # Entries added by HostAliases.
-123.45.67.89	foo
-123.45.67.89	bar
-123.45.67.89	baz
+123.45.67.89	foo	bar	baz
 `,
 		},
 		{
@@ -214,12 +212,8 @@ fe00::2	ip6-allrouters
 12.34.56.78	another.domain
 
 # Entries added by HostAliases.
-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
+123.45.67.89	foo	bar	baz
+456.78.90.123	park	doo	boo
 `,
 		},
 	}
@@ -300,9 +294,7 @@ fe00::2	ip6-allrouters
 203.0.113.1	podFoo.domainFoo	podFoo
 
 # Entries added by HostAliases.
-123.45.67.89	foo
-123.45.67.89	bar
-123.45.67.89	baz
+123.45.67.89	foo	bar	baz
 `,
 		},
 		{
@@ -323,12 +315,8 @@ fe00::2	ip6-allrouters
 203.0.113.1	podFoo.domainFoo	podFoo
 
 # Entries added by HostAliases.
-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
+123.45.67.89	foo	bar	baz
+456.78.90.123	park	doo	boo
 `,
 		},
 	}

test/e2e/common/kubelet.go

@@ -175,7 +175,7 @@ var _ = framework.KubeDescribe("Kubelet", func() {
 				buf.ReadFrom(rc)
 				hostsFileContent := buf.String()
 
-				if !strings.Contains(hostsFileContent, "123.45.67.89\tfoo") || !strings.Contains(hostsFileContent, "123.45.67.89\tbar") {
+				if !strings.Contains(hostsFileContent, "123.45.67.89\tfoo\tbar") {
 					return fmt.Errorf("expected hosts file to contain entries from HostAliases. Got:\n%+v", hostsFileContent)
 				}