etcdctlv3: elect command

etcdctlv3/README.md

@@ -282,6 +282,43 @@ mylock/1234534535445
 
 ```
 
+### Notes
+
+The lease length of a lock defaults to 60 seconds. If LOCK is abnormally terminated, lock progress may be delayed
+by up to 60 seconds.
+
+
+### ELECT [options] \<election-name\> [proposal]
+
+ELECT participates on a named election. A node announces its candidacy in the election by providing
+a proposal value. If a node wishes to observe the election, ELECT listens for new leaders values.
+Whenever a leader is elected, its proposal is given as output.
+
+#### Options
+
+- listen -- observe the election
+
+#### Return value
+
+- If a candidate, ELECT displays the GET on the leader key once the node is elected election.
+
+- If observing, ELECT streams the result for a GET on the leader key for the current election and all future elections.
+
+- ELECT returns a zero exit code only if it is terminated by a signal and can revoke its candidacy or leadership, if any.
+
+#### Example
+```bash
+./etcdctl elect myelection foo
+myelection/1456952310051373265
+foo
+
+```
+
+### Notes
+
+The lease length of a leader defaults to 60 seconds. If a candidate is abnormally terminated, election
+progress may be delayed by up to 60 seconds.
+
 
 ### MAKE-MIRROR [options] \<destination\>
 

etcdctlv3/command/elect_command.go

@@ -0,0 +1,132 @@
+// Copyright 2016 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package command
+
+import (
+	"errors"
+	"os"
+	"os/signal"
+
+	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/spf13/cobra"
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
+)
+
+var (
+	electListen bool
+)
+
+// NewElectCommand returns the cobra command for "elect".
+func NewElectCommand() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "elect <election-name> [proposal]",
+		Short: "elect observes and participates in leader election",
+		Run:   electCommandFunc,
+	}
+	cmd.Flags().BoolVarP(&electListen, "listen", "l", false, "observation mode")
+	return cmd
+}
+
+func electCommandFunc(cmd *cobra.Command, args []string) {
+	if len(args) != 1 && len(args) != 2 {
+		ExitWithError(ExitBadArgs, errors.New("elect takes one election name argument and an optional proposal argument."))
+	}
+	c := mustClientFromCmd(cmd)
+
+	var err error
+	if len(args) == 1 {
+		if !electListen {
+			ExitWithError(ExitBadArgs, errors.New("no proposal argument but -l not set"))
+		}
+		err = observe(c, args[0])
+	} else {
+		if electListen {
+			ExitWithError(ExitBadArgs, errors.New("proposal given but -l is set"))
+		}
+		err = campaign(c, args[0], args[1])
+	}
+	if err != nil {
+		ExitWithError(ExitError, err)
+	}
+}
+
+func observe(c *clientv3.Client, election string) error {
+	e := concurrency.NewElection(context.TODO(), c, election)
+	ctx, cancel := context.WithCancel(context.TODO())
+
+	donec := make(chan struct{})
+	sigc := make(chan os.Signal, 1)
+	signal.Notify(sigc, os.Interrupt, os.Kill)
+	go func() {
+		<-sigc
+		cancel()
+	}()
+
+	go func() {
+		for resp := range e.Observe(ctx) {
+			display.Get(resp)
+		}
+		close(donec)
+	}()
+
+	<-donec
+
+	select {
+	case <-ctx.Done():
+	default:
+		return errors.New("elect: observer lost")
+	}
+
+	return nil
+}
+
+func campaign(c *clientv3.Client, election string, prop string) error {
+	e := concurrency.NewElection(context.TODO(), c, election)
+	ctx, cancel := context.WithCancel(context.TODO())
+
+	donec := make(chan struct{})
+	sigc := make(chan os.Signal, 1)
+	signal.Notify(sigc, os.Interrupt, os.Kill)
+	go func() {
+		<-sigc
+		cancel()
+		close(donec)
+	}()
+
+	s, serr := concurrency.NewSession(c)
+	if serr != nil {
+		return serr
+	}
+
+	if err := e.Campaign(ctx, prop); err != nil {
+		return err
+	}
+
+	// print key since elected
+	resp, err := c.Get(ctx, e.Key())
+	if err != nil {
+		return err
+	}
+	display.Get(*resp)
+
+	select {
+	case <-donec:
+	case <-s.Done():
+		return errors.New("elect: session expired")
+	}
+
+	return e.Resign()
+}

etcdctlv3/main.go

@@ -64,6 +64,7 @@ func init() {
 		command.NewMakeMirrorCommand(),
 		command.NewLockCommand(),
 		command.NewAuthCommand(),
+		command.NewElectCommand(),
 	)
 }