Add flag `--host` to `service create` and `--host-add/--host-rm` to `service update`

This fix tries to address 27902 by adding a flag `--host`
to `docker service create` and `--host-add/--host-rm` to
`docker service update`, so that it is possible to
specify extra `host:ip` settings in `/etc/hosts`.

This fix adds `Hosts` in swarmkit's `ContainerSpec` so that it
is possible to specify extra hosts during service creation.

Related docs has been updated.

An integration test has been added.

This fix fixes 27902.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

command/service/create.go

@@ -45,6 +45,7 @@ func newCreateCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.Var(&opts.dns, flagDNS, "Set custom DNS servers")
 	flags.Var(&opts.dnsOption, flagDNSOption, "Set DNS options")
 	flags.Var(&opts.dnsSearch, flagDNSSearch, "Set custom DNS search domains")
+	flags.Var(&opts.hosts, flagHost, "Set one or more custom host-to-IP mappings (host:ip)")
 
 	flags.SetInterspersed(false)
 	return cmd

command/service/opts.go

@@ -397,6 +397,20 @@ func ValidatePort(value string) (string, error) {
 	return value, err
 }
 
+// convertExtraHostsToSwarmHosts converts an array of extra hosts in cli
+//     <host>:<ip>
+// into a swarmkit host format:
+//     IP_address canonical_hostname [aliases...]
+// This assumes input value (<host>:<ip>) has already been validated
+func convertExtraHostsToSwarmHosts(extraHosts []string) []string {
+	hosts := []string{}
+	for _, extraHost := range extraHosts {
+		parts := strings.SplitN(extraHost, ":", 2)
+		hosts = append(hosts, fmt.Sprintf("%s %s", parts[1], parts[0]))
+	}
+	return hosts
+}
+
 type serviceOptions struct {
 	name            string
 	labels          opts.ListOpts
@@ -414,6 +428,7 @@ type serviceOptions struct {
 	dns             opts.ListOpts
 	dnsSearch       opts.ListOpts
 	dnsOption       opts.ListOpts
+	hosts           opts.ListOpts
 
 	resources resourceOptions
 	stopGrace DurationOpt
@@ -450,6 +465,7 @@ func newServiceOptions() *serviceOptions {
 		dns:       opts.NewListOpts(opts.ValidateIPAddress),
 		dnsOption: opts.NewListOpts(nil),
 		dnsSearch: opts.NewListOpts(opts.ValidateDNSSearch),
+		hosts:     opts.NewListOpts(runconfigopts.ValidateExtraHost),
 		networks:  opts.NewListOpts(nil),
 	}
 }
@@ -498,6 +514,7 @@ func (opts *serviceOptions) ToService() (swarm.ServiceSpec, error) {
 					Search:      opts.dnsSearch.GetAll(),
 					Options:     opts.dnsOption.GetAll(),
 				},
+				Hosts:           convertExtraHostsToSwarmHosts(opts.hosts.GetAll()),
 				StopGracePeriod: opts.stopGrace.Value(),
 				Secrets:         nil,
 			},
@@ -604,6 +621,9 @@ const (
 	flagDNSSearchRemove       = "dns-search-rm"
 	flagDNSSearchAdd          = "dns-search-add"
 	flagEndpointMode          = "endpoint-mode"
+	flagHost                  = "host"
+	flagHostAdd               = "host-add"
+	flagHostRemove            = "host-rm"
 	flagHostname              = "hostname"
 	flagEnv                   = "env"
 	flagEnvFile               = "env-file"

command/service/update.go

@@ -52,6 +52,7 @@ func newUpdateCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.Var(newListOptsVar(), flagDNSRemove, "Remove a custom DNS server")
 	flags.Var(newListOptsVar(), flagDNSOptionRemove, "Remove a DNS option")
 	flags.Var(newListOptsVar(), flagDNSSearchRemove, "Remove a DNS search domain")
+	flags.Var(newListOptsVar(), flagHostRemove, "Remove a custom host-to-IP mapping (host:ip)")
 	flags.Var(&opts.labels, flagLabelAdd, "Add or update a service label")
 	flags.Var(&opts.containerLabels, flagContainerLabelAdd, "Add or update a container label")
 	flags.Var(&opts.env, flagEnvAdd, "Add or update an environment variable")
@@ -64,6 +65,7 @@ func newUpdateCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.Var(&opts.dns, flagDNSAdd, "Add or update a custom DNS server")
 	flags.Var(&opts.dnsOption, flagDNSOptionAdd, "Add or update a DNS option")
 	flags.Var(&opts.dnsSearch, flagDNSSearchAdd, "Add or update a custom DNS search domain")
+	flags.Var(&opts.hosts, flagHostAdd, "Add or update a custom host-to-IP mapping (host:ip)")
 
 	return cmd
 }
@@ -283,6 +285,12 @@ func updateService(flags *pflag.FlagSet, spec *swarm.ServiceSpec) error {
 		}
 	}
 
+	if anyChanged(flags, flagHostAdd, flagHostRemove) {
+		if err := updateHosts(flags, &cspec.Hosts); err != nil {
+			return err
+		}
+	}
+
 	if err := updateLogDriver(flags, &spec.TaskTemplate); err != nil {
 		return err
 	}
@@ -683,6 +691,47 @@ func updateReplicas(flags *pflag.FlagSet, serviceMode *swarm.ServiceMode) error
 	return nil
 }
 
+func updateHosts(flags *pflag.FlagSet, hosts *[]string) error {
+	// Combine existing Hosts (in swarmkit format) with the host to add (convert to swarmkit format)
+	if flags.Changed(flagHostAdd) {
+		values := convertExtraHostsToSwarmHosts(flags.Lookup(flagHostAdd).Value.(*opts.ListOpts).GetAll())
+		*hosts = append(*hosts, values...)
+	}
+	// Remove duplicate
+	*hosts = removeDuplicates(*hosts)
+
+	keysToRemove := make(map[string]struct{})
+	if flags.Changed(flagHostRemove) {
+		var empty struct{}
+		extraHostsToRemove := flags.Lookup(flagHostRemove).Value.(*opts.ListOpts).GetAll()
+		for _, entry := range extraHostsToRemove {
+			key := strings.SplitN(entry, ":", 2)[0]
+			keysToRemove[key] = empty
+		}
+	}
+
+	newHosts := []string{}
+	for _, entry := range *hosts {
+		// Since this is in swarmkit format, we need to find the key, which is canonical_hostname of:
+		// IP_address canonical_hostname [aliases...]
+		parts := strings.Fields(entry)
+		if len(parts) > 1 {
+			key := parts[1]
+			if _, exists := keysToRemove[key]; !exists {
+				newHosts = append(newHosts, entry)
+			}
+		} else {
+			newHosts = append(newHosts, entry)
+		}
+	}
+
+	// Sort so that result is predictable.
+	sort.Strings(newHosts)
+
+	*hosts = newHosts
+	return nil
+}
+
 // updateLogDriver updates the log driver only if the log driver flag is set.
 // All options will be replaced with those provided on the command line.
 func updateLogDriver(flags *pflag.FlagSet, taskTemplate *swarm.TaskSpec) error {

command/service/update_test.go

@@ -339,3 +339,23 @@ func TestUpdateHealthcheckTable(t *testing.T) {
 		}
 	}
 }
+
+func TestUpdateHosts(t *testing.T) {
+	flags := newUpdateCommand(nil).Flags()
+	flags.Set("host-add", "example.net:2.2.2.2")
+	flags.Set("host-add", "ipv6.net:2001:db8:abc8::1")
+	// remove with ipv6 should work
+	flags.Set("host-rm", "example.net:2001:db8:abc8::1")
+	// just hostname should work as well
+	flags.Set("host-rm", "example.net")
+	// bad format error
+	assert.Error(t, flags.Set("host-add", "$example.com$"), "bad format for add-host:")
+
+	hosts := []string{"1.2.3.4 example.com", "4.3.2.1 example.org", "2001:db8:abc8::1 example.net"}
+
+	updateHosts(flags, &hosts)
+	assert.Equal(t, len(hosts), 3)
+	assert.Equal(t, hosts[0], "1.2.3.4 example.com")
+	assert.Equal(t, hosts[1], "2001:db8:abc8::1 ipv6.net")
+	assert.Equal(t, hosts[2], "4.3.2.1 example.org")
+}