Allow swarm join with --availability=drain

This fix tries to address the issue raised in 24596 where it was not
possible to join as manager only (`--availability=drain`).

This fix adds a new flag `--availability` to `swarm join`.

Related documentation has been updated.

An integration test has been added.

NOTE: Additional pull request for swarmkit and engine-api will
be created separately.

This fix fixes 24596.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Upstream-commit: ab2635ead0
Component: cli

components/cli/command/swarm/join.go

@@ -2,12 +2,15 @@ package swarm
 
 import (
 	"fmt"
+	"strings"
+
+	"golang.org/x/net/context"
 
 	"github.com/docker/docker/api/types/swarm"
 	"github.com/docker/docker/cli"
 	"github.com/docker/docker/cli/command"
 	"github.com/spf13/cobra"
-	"golang.org/x/net/context"
+	"github.com/spf13/pflag"
 )
 
 type joinOptions struct {
@@ -16,6 +19,7 @@ type joinOptions struct {
 	// Not a NodeAddrOption because it has no default port.
 	advertiseAddr string
 	token         string
+	availability  string
 }
 
 func newJoinCommand(dockerCli command.Cli) *cobra.Command {
@@ -29,7 +33,7 @@ func newJoinCommand(dockerCli command.Cli) *cobra.Command {
 		Args:  cli.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			opts.remote = args[0]
-			return runJoin(dockerCli, opts)
+			return runJoin(dockerCli, cmd.Flags(), opts)
 		},
 	}
 
@@ -37,10 +41,11 @@ func newJoinCommand(dockerCli command.Cli) *cobra.Command {
 	flags.Var(&opts.listenAddr, flagListenAddr, "Listen address (format: <ip|interface>[:port])")
 	flags.StringVar(&opts.advertiseAddr, flagAdvertiseAddr, "", "Advertised address (format: <ip|interface>[:port])")
 	flags.StringVar(&opts.token, flagToken, "", "Token for entry into the swarm")
+	flags.StringVar(&opts.availability, flagAvailability, "active", "Availability of the node (active/pause/drain)")
 	return cmd
 }
 
-func runJoin(dockerCli command.Cli, opts joinOptions) error {
+func runJoin(dockerCli command.Cli, flags *pflag.FlagSet, opts joinOptions) error {
 	client := dockerCli.Client()
 	ctx := context.Background()
 
@@ -50,6 +55,16 @@ func runJoin(dockerCli command.Cli, opts joinOptions) error {
 		AdvertiseAddr: opts.advertiseAddr,
 		RemoteAddrs:   []string{opts.remote},
 	}
+	if flags.Changed(flagAvailability) {
+		availability := swarm.NodeAvailability(strings.ToLower(opts.availability))
+		switch availability {
+		case swarm.NodeAvailabilityActive, swarm.NodeAvailabilityPause, swarm.NodeAvailabilityDrain:
+			req.Availability = availability
+		default:
+			return fmt.Errorf("invalid availability %q, only active, pause and drain are supported", opts.availability)
+		}
+	}
+
 	err := client.SwarmJoin(ctx, req)
 	if err != nil {
 		return err

components/cli/command/swarm/opts.go

@@ -28,6 +28,7 @@ const (
 	flagSnapshotInterval    = "snapshot-interval"
 	flagLockKey             = "lock-key"
 	flagAutolock            = "autolock"
+	flagAvailability        = "availability"
 )
 
 type swarmOptions struct {