Add custom DNS settings to service definition

This fix tries to fix the issue raised in 24391 about allowing
custom DNS settings to service definition.

This fix adds `DNSConfig` (`Nameservers`, `Options`, `Search`) to
service definition, as well as `--dns`, `--dns-opt`, and `dns-search`
to `service create`.

An integration test has been added to cover the changes in this fix.

This fix fixes 24391.

A PR in swarmkit will be created separately.

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

command/service/create.go

@@ -41,6 +41,9 @@ func newCreateCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.StringSliceVar(&opts.networks, flagNetwork, []string{}, "Network attachments")
 	flags.VarP(&opts.endpoint.ports, flagPublish, "p", "Publish a port as a node port")
 	flags.StringSliceVar(&opts.groups, flagGroup, []string{}, "Set one or more supplementary user groups for the container")
+	flags.Var(&opts.dns, flagDNS, "Set custom DNS servers")
+	flags.Var(&opts.dnsOptions, flagDNSOptions, "Set DNS options")
+	flags.Var(&opts.dnsSearch, flagDNSSearch, "Set custom DNS search domains")
 
 	flags.SetInterspersed(false)
 	return cmd

command/service/opts.go

@@ -296,6 +296,9 @@ type serviceOptions struct {
 	groups          []string
 	tty             bool
 	mounts          opts.MountOpt
+	dns             opts.ListOpts
+	dnsSearch       opts.ListOpts
+	dnsOptions      opts.ListOpts
 
 	resources resourceOptions
 	stopGrace DurationOpt
@@ -326,6 +329,9 @@ func newServiceOptions() *serviceOptions {
 			ports: opts.NewListOpts(ValidatePort),
 		},
 		logDriver:  newLogDriverOptions(),
+		dns:        opts.NewListOpts(opts.ValidateIPAddress),
+		dnsOptions: opts.NewListOpts(nil),
+		dnsSearch:  opts.NewListOpts(opts.ValidateDNSSearch),
 	}
 }
 
@@ -368,6 +374,11 @@ func (opts *serviceOptions) ToService() (swarm.ServiceSpec, error) {
 				Groups:   opts.groups,
 				TTY:      opts.tty,
 				Mounts:   opts.mounts.Value(),
+				DNSConfig: &swarm.DNSConfig{
+					Nameservers: opts.dns.GetAll(),
+					Search:      opts.dnsSearch.GetAll(),
+					Options:     opts.dnsOptions.GetAll(),
+				},
 				StopGracePeriod: opts.stopGrace.Value(),
 			},
 			Networks:      convertNetworks(opts.networks),
@@ -463,6 +474,9 @@ const (
 	flagContainerLabel        = "container-label"
 	flagContainerLabelRemove  = "container-label-rm"
 	flagContainerLabelAdd     = "container-label-add"
+	flagDNS                   = "dns"
+	flagDNSOptions            = "dns-opt"
+	flagDNSSearch             = "dns-search"
 	flagEndpointMode          = "endpoint-mode"
 	flagHostname              = "hostname"
 	flagEnv                   = "env"