Allow extra lines in /etc/hosts

This adds a --add-host host:ip flag which appends lines to /etc/hosts.  This is needed in places where you want the container to get a different name resolution than it would through DNS.  This was submitted before as #5525, closed, and now I am re-opening.  It has come up 2 or 3 times in the last couple days.

Signed-off-by: Tim Hockin <thockin@google.com>

daemon/container.go

@@ -422,6 +422,11 @@ func (container *Container) buildHostsFiles(IP string) error {
 		extraContent[alias] = child.NetworkSettings.IPAddress
 	}
 
+	for _, extraHost := range container.hostConfig.ExtraHosts {
+		parts := strings.Split(extraHost, ":")
+		extraContent[parts[0]] = parts[1]
+	}
+
 	return etchosts.Build(container.HostsPath, IP, container.Config.Hostname, container.Config.Domainname, &extraContent)
 }
 

docs/man/docker-run.1.md

@@ -7,6 +7,7 @@ docker-run - Run a command in a new container
 # SYNOPSIS
 **docker run**
 [**-a**|**--attach**[=*[]*]]
+[**--add-host**[=*[]*]]
 [**-c**|**--cpu-shares**[=*0*]]
 [**--cap-add**[=*[]*]]
 [**--cap-drop**[=*[]*]]
@@ -64,6 +65,10 @@ error. It can even pretend to be a TTY (this is what most commandline
 executables expect) and pass along signals. The **-a** option can be set for
 each of stdin, stdout, and stderr.
 
+**--add-host**=*hostname*:*ip*
+   Add a line to /etc/hosts. The format is hostname:ip.  The **--add-host**
+option can be set multiple times.
+
 **-c**, **--cpu-shares**=0
    CPU shares in relative weight. You can increase the priority of a container
 with the -c option. By default, all containers run at the same priority and get

docs/sources/reference/commandline/cli.md

@@ -986,6 +986,7 @@ removed before the image is removed.
     Run a command in a new container
 
       -a, --attach=[]            Attach to STDIN, STDOUT or STDERR.
+      --add-host=[]              Add a custom host-to-IP mapping (host:ip)
       -c, --cpu-shares=0         CPU shares (relative weight)
       --cap-add=[]               Add Linux capabilities
       --cap-drop=[]              Drop Linux capabilities

docs/sources/reference/run.md

@@ -139,6 +139,7 @@ example, `docker run ubuntu:14.04`.
                                  'none': no networking for this container
                                  'container:<name|id>': reuses another container network stack
                                  'host': use the host network stack inside the container
+    --add-host=""   : Add a line to /etc/hosts (host:IP)
 
 By default, all containers have networking enabled and they can make any
 outgoing connections. The operator can completely disable networking
@@ -196,6 +197,22 @@ running the `redis-cli` command and connecting to the Redis server over the
     $ # use the redis container's network stack to access localhost
     $ sudo docker run --rm -ti --net container:redis example/redis-cli -h 127.0.0.1
 
+### Managing /etc/hosts
+
+Your container will have lines in `/etc/hosts` which define the hostname of the
+container itself as well as `localhost` and a few other common things.  The
+`--add-host` flag can be used to add additional lines to `/etc/hosts`.  
+
+    $ /docker run -ti --add-host db-static:86.75.30.9 ubuntu cat /etc/hosts
+    172.17.0.22     09d03f76bf2c
+    fe00::0         ip6-localnet
+    ff00::0         ip6-mcastprefix
+    ff02::1         ip6-allnodes
+    ff02::2         ip6-allrouters
+    127.0.0.1       localhost
+    ::1	            localhost ip6-localhost ip6-loopback
+    86.75.30.9      db-static
+
 ## Clean Up (–-rm)
 
 By default a container's file system persists even after the container

integration-cli/docker_cli_run_test.go

@@ -1331,6 +1331,23 @@ func TestDnsOptionsBasedOnHostResolvConf(t *testing.T) {
 	logDone("run - dns options based on host resolv.conf")
 }
 
+func TestRunAddHost(t *testing.T) {
+	defer deleteAllContainers()
+	cmd := exec.Command(dockerBinary, "run", "--add-host=extra:86.75.30.9", "busybox", "grep", "extra", "/etc/hosts")
+
+	out, _, err := runCommandWithOutput(cmd)
+	if err != nil {
+		t.Fatal(err, out)
+	}
+
+	actual := strings.Trim(out, "\r\n")
+	if actual != "86.75.30.9\textra" {
+		t.Fatalf("expected '86.75.30.9\textra', but says: '%s'", actual)
+	}
+
+	logDone("run - add-host option")
+}
+
 // Regression test for #6983
 func TestAttachStdErrOnlyTTYMode(t *testing.T) {
 	cmd := exec.Command(dockerBinary, "run", "-t", "-a", "stderr", "busybox", "true")

opts/opts.go

@@ -199,6 +199,17 @@ func validateDomain(val string) (string, error) {
 	return "", fmt.Errorf("%s is not a valid domain", val)
 }
 
+func ValidateExtraHost(val string) (string, error) {
+	arr := strings.Split(val, ":")
+	if len(arr) != 2 || len(arr[0]) == 0 {
+		return "", fmt.Errorf("bad format for add-host: %s", val)
+	}
+	if _, err := ValidateIPAddress(arr[1]); err != nil {
+		return "", fmt.Errorf("bad format for add-host: %s", val)
+	}
+	return val, nil
+}
+
 // Validates an HTTP(S) registry mirror
 func ValidateMirror(val string) (string, error) {
 	uri, err := url.Parse(val)

runconfig/hostconfig.go

@@ -49,6 +49,7 @@ type HostConfig struct {
 	PublishAllPorts bool
 	Dns             []string
 	DnsSearch       []string
+	ExtraHosts      []string
 	VolumesFrom     []string
 	Devices         []DeviceMapping
 	NetworkMode     NetworkMode
@@ -81,6 +82,9 @@ func ContainerHostConfigFromJob(job *engine.Job) *HostConfig {
 	if DnsSearch := job.GetenvList("DnsSearch"); DnsSearch != nil {
 		hostConfig.DnsSearch = DnsSearch
 	}
+	if ExtraHosts := job.GetenvList("ExtraHosts"); ExtraHosts != nil {
+		hostConfig.ExtraHosts = ExtraHosts
+	}
 	if VolumesFrom := job.GetenvList("VolumesFrom"); VolumesFrom != nil {
 		hostConfig.VolumesFrom = VolumesFrom
 	}

runconfig/parse.go

@@ -54,6 +54,7 @@ func parseRun(cmd *flag.FlagSet, args []string, sysInfo *sysinfo.SysInfo) (*Conf
 		flExpose      = opts.NewListOpts(nil)
 		flDns         = opts.NewListOpts(opts.ValidateIPAddress)
 		flDnsSearch   = opts.NewListOpts(opts.ValidateDnsSearch)
+		flExtraHosts  = opts.NewListOpts(opts.ValidateExtraHost)
 		flVolumesFrom = opts.NewListOpts(nil)
 		flLxcOpts     = opts.NewListOpts(nil)
 		flEnvFile     = opts.NewListOpts(nil)
@@ -93,6 +94,7 @@ func parseRun(cmd *flag.FlagSet, args []string, sysInfo *sysinfo.SysInfo) (*Conf
 	cmd.Var(&flExpose, []string{"#expose", "-expose"}, "Expose a port from the container without publishing it to your host")
 	cmd.Var(&flDns, []string{"#dns", "-dns"}, "Set custom DNS servers")
 	cmd.Var(&flDnsSearch, []string{"-dns-search"}, "Set custom DNS search domains")
+	cmd.Var(&flExtraHosts, []string{"-add-host"}, "Add a custom host-to-IP mapping (host:ip)")
 	cmd.Var(&flVolumesFrom, []string{"#volumes-from", "-volumes-from"}, "Mount volumes from the specified container(s)")
 	cmd.Var(&flLxcOpts, []string{"#lxc-conf", "-lxc-conf"}, "(lxc exec-driver only) Add custom lxc options --lxc-conf=\"lxc.cgroup.cpuset.cpus = 0,1\"")
 
@@ -291,6 +293,7 @@ func parseRun(cmd *flag.FlagSet, args []string, sysInfo *sysinfo.SysInfo) (*Conf
 		PublishAllPorts: *flPublishAll,
 		Dns:             flDns.GetAll(),
 		DnsSearch:       flDnsSearch.GetAll(),
+		ExtraHosts:      flExtraHosts.GetAll(),
 		VolumesFrom:     flVolumesFrom.GetAll(),
 		NetworkMode:     netMode,
 		Devices:         deviceMappings,