| // Copyright 2016 The etcd Authors |
| // |
| // 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 ( |
| "context" |
| "errors" |
| "os" |
| "os/signal" |
| "syscall" |
| |
| "github.com/coreos/etcd/clientv3" |
| "github.com/coreos/etcd/clientv3/concurrency" |
| |
| "github.com/spf13/cobra" |
| ) |
| |
| var ( |
| electListen bool |
| ) |
| |
| // NewElectCommand returns the cobra command for "elect". |
| func NewElectCommand() *cobra.Command { |
| cmd := &cobra.Command{ |
| Use: "elect <election-name> [proposal]", |
| Short: "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 { |
| s, err := concurrency.NewSession(c) |
| if err != nil { |
| return err |
| } |
| e := concurrency.NewElection(s, election) |
| ctx, cancel := context.WithCancel(context.TODO()) |
| |
| donec := make(chan struct{}) |
| sigc := make(chan os.Signal, 1) |
| signal.Notify(sigc, syscall.SIGINT, syscall.SIGTERM) |
| 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 { |
| s, err := concurrency.NewSession(c) |
| if err != nil { |
| return err |
| } |
| e := concurrency.NewElection(s, election) |
| ctx, cancel := context.WithCancel(context.TODO()) |
| |
| donec := make(chan struct{}) |
| sigc := make(chan os.Signal, 1) |
| signal.Notify(sigc, syscall.SIGINT, syscall.SIGTERM) |
| go func() { |
| <-sigc |
| cancel() |
| close(donec) |
| }() |
| |
| 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(context.TODO()) |
| } |