Codebase list golang-github-docker-leadership / upstream/0.0_git20160208.0.b545f2d
Imported Upstream version 0.0~git20160208.0.b545f2d Dmitry Smirnov 8 years ago
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CONTRIBUTING.md less more
0 # Contributing to Docker
1
2 ### Sign your work
3
4 The sign-off is a simple line at the end of the explanation for the patch. Your
5 signature certifies that you wrote the patch or otherwise have the right to pass
6 it on as an open-source patch. The rules are pretty simple: if you can certify
7 the below (from [developercertificate.org](http://developercertificate.org/)):
8
9 ```
10 Developer Certificate of Origin
11 Version 1.1
12
13 Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
14 660 York Street, Suite 102,
15 San Francisco, CA 94110 USA
16
17 Everyone is permitted to copy and distribute verbatim copies of this
18 license document, but changing it is not allowed.
19
20 Developer's Certificate of Origin 1.1
21
22 By making a contribution to this project, I certify that:
23
24 (a) The contribution was created in whole or in part by me and I
25 have the right to submit it under the open source license
26 indicated in the file; or
27
28 (b) The contribution is based upon previous work that, to the best
29 of my knowledge, is covered under an appropriate open source
30 license and I have the right under that license to submit that
31 work with modifications, whether created in whole or in part
32 by me, under the same open source license (unless I am
33 permitted to submit under a different license), as indicated
34 in the file; or
35
36 (c) The contribution was provided directly to me by some other
37 person who certified (a), (b) or (c) and I have not modified
38 it.
39
40 (d) I understand and agree that this project and the contribution
41 are public and that a record of the contribution (including all
42 personal information I submit with it, including my sign-off) is
43 maintained indefinitely and may be redistributed consistent with
44 this project or the open source license(s) involved.
45 ```
46
47 Then you just add a line to every git commit message:
48
49 Signed-off-by: Joe Smith <joe.smith@email.com>
50
51 Use your real name (sorry, no pseudonyms or anonymous contributions.)
52
53 If you set your `user.name` and `user.email` git configs, you can sign your
54 commit automatically with `git commit -s`.
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LICENSE less more
0
1 Apache License
2 Version 2.0, January 2004
3 https://www.apache.org/licenses/
4
5 TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
6
7 1. Definitions.
8
9 "License" shall mean the terms and conditions for use, reproduction,
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22
23 "You" (or "Your") shall mean an individual or Legal Entity
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26 "Source" form shall mean the preferred form for making modifications,
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28 source, and configuration files.
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34
35 "Work" shall mean the work of authorship, whether in Source or
36 Object form, made available under the License, as indicated by a
37 copyright notice that is included in or attached to the work
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40 "Derivative Works" shall mean any work, whether in Source or Object
41 form, that is based on (or derived from) the Work and for which the
42 editorial revisions, annotations, elaborations, or other modifications
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45 separable from, or merely link (or bind by name) to the interfaces of,
46 the Work and Derivative Works thereof.
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48 "Contribution" shall mean any work of authorship, including
49 the original version of the Work and any modifications or additions
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62 "Contributor" shall mean Licensor and any individual or Legal Entity
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82 institute patent litigation against any entity (including a
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88
89 4. Redistribution. You may reproduce and distribute copies of the
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92 meet the following conditions:
93
94 (a) You must give any other recipients of the Work or
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96
97 (b) You must cause any modified files to carry prominent notices
98 stating that You changed the files; and
99
100 (c) You must retain, in the Source form of any Derivative Works
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105
106 (d) If the Work includes a "NOTICE" text file as part of its
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116 of the NOTICE file are for informational purposes only and
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118 notices within Derivative Works that You distribute, alongside
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122
123 You may add Your own copyright statement to Your modifications and
124 may provide additional or different license terms and conditions
125 for use, reproduction, or distribution of Your modifications, or
126 for any such Derivative Works as a whole, provided Your use,
127 reproduction, and distribution of the Work otherwise complies with
128 the conditions stated in this License.
129
130 5. Submission of Contributions. Unless You explicitly state otherwise,
131 any Contribution intentionally submitted for inclusion in the Work
132 by You to the Licensor shall be under the terms and conditions of
133 this License, without any additional terms or conditions.
134 Notwithstanding the above, nothing herein shall supersede or modify
135 the terms of any separate license agreement you may have executed
136 with Licensor regarding such Contributions.
137
138 6. Trademarks. This License does not grant permission to use the trade
139 names, trademarks, service marks, or product names of the Licensor,
140 except as required for reasonable and customary use in describing the
141 origin of the Work and reproducing the content of the NOTICE file.
142
143 7. Disclaimer of Warranty. Unless required by applicable law or
144 agreed to in writing, Licensor provides the Work (and each
145 Contributor provides its Contributions) on an "AS IS" BASIS,
146 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
147 implied, including, without limitation, any warranties or conditions
148 of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
149 PARTICULAR PURPOSE. You are solely responsible for determining the
150 appropriateness of using or redistributing the Work and assume any
151 risks associated with Your exercise of permissions under this License.
152
153 8. Limitation of Liability. In no event and under no legal theory,
154 whether in tort (including negligence), contract, or otherwise,
155 unless required by applicable law (such as deliberate and grossly
156 negligent acts) or agreed to in writing, shall any Contributor be
157 liable to You for damages, including any direct, indirect, special,
158 incidental, or consequential damages of any character arising as a
159 result of this License or out of the use or inability to use the
160 Work (including but not limited to damages for loss of goodwill,
161 work stoppage, computer failure or malfunction, or any and all
162 other commercial damages or losses), even if such Contributor
163 has been advised of the possibility of such damages.
164
165 9. Accepting Warranty or Additional Liability. While redistributing
166 the Work or Derivative Works thereof, You may choose to offer,
167 and charge a fee for, acceptance of support, warranty, indemnity,
168 or other liability obligations and/or rights consistent with this
169 License. However, in accepting such obligations, You may act only
170 on Your own behalf and on Your sole responsibility, not on behalf
171 of any other Contributor, and only if You agree to indemnify,
172 defend, and hold each Contributor harmless for any liability
173 incurred by, or claims asserted against, such Contributor by reason
174 of your accepting any such warranty or additional liability.
175
176 END OF TERMS AND CONDITIONS
177
178 Copyright 2015 Docker, Inc.
179
180 Licensed under the Apache License, Version 2.0 (the "License");
181 you may not use this file except in compliance with the License.
182 You may obtain a copy of the License at
183
184 https://www.apache.org/licenses/LICENSE-2.0
185
186 Unless required by applicable law or agreed to in writing, software
187 distributed under the License is distributed on an "AS IS" BASIS,
188 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
189 See the License for the specific language governing permissions and
190 limitations under the License.
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MAINTAINERS less more
0 # leadership maintainers file
1 #
2 # This file describes who runs the docker/leadership project and how.
3 # This is a living document - if you see something out of date or missing, speak up!
4 #
5 # It is structured to be consumable by both humans and programs.
6 # To extract its contents programmatically, use any TOML-compliant parser.
7 #
8 # This file is compiled into the MAINTAINERS file in docker/opensource.
9 #
10 [Org]
11 [Org."Core maintainers"]
12 people = [
13 "abronan",
14 ]
15
16 [people]
17
18 # A reference list of all people associated with the project.
19 # All other sections should refer to people by their canonical key
20 # in the people section.
21
22 # ADD YOURSELF HERE IN ALPHABETICAL ORDER
23 [people.abronan]
24 Name = "Alexandre Beslic"
25 Email = "alexandre.beslic@gmail.com"
26 GitHub = "abronan"
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README.md less more
0 # Leadership: Distributed Leader Election for Clustered Environments.
1
2 Leadership is a library for a cluster leader election on top of a distributed
3 Key/Value store.
4
5 It is built using the `docker/libkv` library and is designed to work across multiple
6 storage backends.
7
8 You can use `leadership` with `Consul`, `etcd` and `Zookeeper`.
9
10 ```go
11 // Create a store using pkg/store.
12 client, err := store.NewStore("consul", []string{"127.0.0.1:8500"}, &store.Config{})
13 if err != nil {
14 panic(err)
15 }
16
17 underwood := leadership.NewCandidate(client, "service/swarm/leader", "underwood", 15*time.Second)
18 electedCh, _, err := underwood.RunForElection()
19 if err != nil {
20 log.Fatal("Cannot run for election, store is probably down")
21 }
22
23 for isElected := range electedCh {
24 // This loop will run every time there is a change in our leadership
25 // status.
26
27 if isElected {
28 // We won the election - we are now the leader.
29 // Let's do leader stuff, for example, sleep for a while.
30 log.Printf("I won the election! I'm now the leader")
31 time.Sleep(10 * time.Second)
32
33 // Tired of being a leader? You can resign anytime.
34 candidate.Resign()
35 } else {
36 // We lost the election but are still running for leadership.
37 // `elected == false` is the default state and is the first event
38 // we'll receive from the channel. After a successful election,
39 // this event can get triggered if someone else steals the
40 // leadership or if we resign.
41
42 log.Printf("Lost the election, let's try another time")
43 }
44 }
45 ```
46
47 It is possible to follow an election in real-time and get notified whenever
48 there is a change in leadership:
49 ```go
50 follower := leadership.NewFollower(client, "service/swarm/leader")
51 leaderCh, _, err := follower.FollowElection()
52 if err != nil {
53 log.Fatal("Cannot follow the election, store is probably down")
54 }
55 for leader := range leaderCh {
56 // Leader is a string containing the value passed to `NewCandidate`.
57 log.Printf("%s is now the leader", leader)
58 }
59 ```
60
61 A typical use case for this is to be able to always send requests to the current
62 leader.
63
64 ## Fault tolerance
65
66 Leadership returns an error channel for Candidates and Followers that you can use
67 to be resilient to failures. For example, if the watch on the leader key fails
68 because the store becomes unavailable, you can retry the process later.
69
70 ```go
71 func participate() {
72 // Create a store using pkg/store.
73 client, err := store.NewStore("consul", []string{"127.0.0.1:8500"}, &store.Config{})
74 if err != nil {
75 panic(err)
76 }
77
78 waitTime := 10 * time.Second
79 underwood := leadership.NewCandidate(client, "service/swarm/leader", "underwood", 15*time.Second)
80
81 go func() {
82 for {
83 run(underwood)
84 time.Sleep(waitTime)
85 // retry
86 }
87 }
88 }
89
90 func run(candidate *leadership.Candidate) {
91 electedCh, errCh, err := candidate.RunForElection()
92 if err != nil {
93 return
94 }
95 for {
96 select {
97 case elected := <-electedCh:
98 if isElected {
99 // Do something
100 } else {
101 // Do something else
102 }
103
104 case err := <-errCh:
105 log.Error(err)
106 return
107 }
108 }
109 ```
110
111 ## License
112
113 leadership is licensed under the Apache License, Version 2.0. See [LICENSE](LICENSE) for the full license text.
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candidate.go less more
0 package leadership
1
2 import (
3 "sync"
4 "time"
5
6 "github.com/docker/libkv/store"
7 )
8
9 const (
10 defaultLockTTL = 15 * time.Second
11 )
12
13 // Candidate runs the leader election algorithm asynchronously
14 type Candidate struct {
15 client store.Store
16 key string
17 node string
18
19 electedCh chan bool
20 lock sync.Mutex
21 lockTTL time.Duration
22 leader bool
23 stopCh chan struct{}
24 resignCh chan bool
25 errCh chan error
26 }
27
28 // NewCandidate creates a new Candidate
29 func NewCandidate(client store.Store, key, node string, ttl time.Duration) *Candidate {
30 return &Candidate{
31 client: client,
32 key: key,
33 node: node,
34
35 leader: false,
36 lockTTL: ttl,
37 resignCh: make(chan bool),
38 stopCh: make(chan struct{}),
39 }
40 }
41
42 // IsLeader returns true if the candidate is currently a leader.
43 func (c *Candidate) IsLeader() bool {
44 return c.leader
45 }
46
47 // RunForElection starts the leader election algorithm. Updates in status are
48 // pushed through the ElectedCh channel.
49 //
50 // ElectedCh is used to get a channel which delivers signals on
51 // acquiring or losing leadership. It sends true if we become
52 // the leader, and false if we lose it.
53 func (c *Candidate) RunForElection() (<-chan bool, <-chan error, error) {
54 c.electedCh = make(chan bool)
55 c.errCh = make(chan error)
56
57 lockOpts := &store.LockOptions{
58 Value: []byte(c.node),
59 }
60
61 if c.lockTTL != defaultLockTTL {
62 lockOpts.TTL = c.lockTTL
63 lockOpts.RenewLock = make(chan struct{})
64 }
65
66 lock, err := c.client.NewLock(c.key, lockOpts)
67
68 if err != nil {
69 return nil, nil, err
70 }
71
72 go c.campaign(lock)
73
74 return c.electedCh, c.errCh, nil
75 }
76
77 // Stop running for election.
78 func (c *Candidate) Stop() {
79 close(c.stopCh)
80 }
81
82 // Resign forces the candidate to step-down and try again.
83 // If the candidate is not a leader, it doesn't have any effect.
84 // Candidate will retry immediately to acquire the leadership. If no-one else
85 // took it, then the Candidate will end up being a leader again.
86 func (c *Candidate) Resign() {
87 c.lock.Lock()
88 defer c.lock.Unlock()
89
90 if c.leader {
91 c.resignCh <- true
92 }
93 }
94
95 func (c *Candidate) update(status bool) {
96 c.lock.Lock()
97 defer c.lock.Unlock()
98
99 c.leader = status
100 c.electedCh <- status
101 }
102
103 func (c *Candidate) campaign(lock store.Locker) {
104 defer close(c.electedCh)
105 defer close(c.errCh)
106
107 for {
108 // Start as a follower.
109 c.update(false)
110
111 lostCh, err := lock.Lock(nil)
112 if err != nil {
113 c.errCh <- err
114 return
115 }
116
117 // Hooray! We acquired the lock therefore we are the new leader.
118 c.update(true)
119
120 select {
121 case <-c.resignCh:
122 // We were asked to resign, give up the lock and go back
123 // campaigning.
124 lock.Unlock()
125 case <-c.stopCh:
126 // Give up the leadership and quit.
127 if c.leader {
128 lock.Unlock()
129 }
130 return
131 case <-lostCh:
132 // We lost the lock. Someone else is the leader, try again.
133 }
134 }
135 }
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candidate_test.go less more
0 package leadership
1
2 import (
3 "testing"
4 "time"
5
6 libkvmock "github.com/docker/libkv/store/mock"
7 "github.com/stretchr/testify/assert"
8 "github.com/stretchr/testify/mock"
9 )
10
11 func TestCandidate(t *testing.T) {
12 kv, err := libkvmock.New([]string{}, nil)
13 assert.NoError(t, err)
14 assert.NotNil(t, kv)
15
16 mockStore := kv.(*libkvmock.Mock)
17 mockLock := &libkvmock.Lock{}
18 mockStore.On("NewLock", "test_key", mock.Anything).Return(mockLock, nil)
19
20 // Lock and unlock always succeeds.
21 lostCh := make(chan struct{})
22 var mockLostCh <-chan struct{} = lostCh
23 mockLock.On("Lock", mock.Anything).Return(mockLostCh, nil)
24 mockLock.On("Unlock").Return(nil)
25
26 candidate := NewCandidate(kv, "test_key", "test_node", 0)
27 electedCh, _, err := candidate.RunForElection()
28 assert.Nil(t, err)
29
30 // Should issue a false upon start, no matter what.
31 assert.False(t, <-electedCh)
32
33 // Since the lock always succeeeds, we should get elected.
34 assert.True(t, <-electedCh)
35 assert.True(t, candidate.IsLeader())
36
37 // Signaling a lost lock should get us de-elected...
38 close(lostCh)
39 assert.False(t, <-electedCh)
40
41 // And we should attempt to get re-elected again.
42 assert.True(t, <-electedCh)
43
44 // When we resign, unlock will get called, we'll be notified of the
45 // de-election and we'll try to get the lock again.
46 go candidate.Resign()
47 assert.False(t, <-electedCh)
48 assert.True(t, <-electedCh)
49
50 candidate.Stop()
51
52 // Ensure that the chan closes after some time
53 for {
54 select {
55 case _, open := <-electedCh:
56 if !open {
57 mockStore.AssertExpectations(t)
58 return
59 }
60 case <-time.After(1 * time.Second):
61 t.Fatalf("electedCh not closed correctly")
62 }
63 }
64 }
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follower.go less more
0 package leadership
1
2 import (
3 "errors"
4
5 "github.com/docker/libkv/store"
6 )
7
8 // Follower can follow an election in real-time and push notifications whenever
9 // there is a change in leadership.
10 type Follower struct {
11 client store.Store
12 key string
13
14 leader string
15 leaderCh chan string
16 stopCh chan struct{}
17 errCh chan error
18 }
19
20 // NewFollower creates a new follower.
21 func NewFollower(client store.Store, key string) *Follower {
22 return &Follower{
23 client: client,
24 key: key,
25 stopCh: make(chan struct{}),
26 }
27 }
28
29 // Leader returns the current leader.
30 func (f *Follower) Leader() string {
31 return f.leader
32 }
33
34 // FollowElection starts monitoring the election.
35 func (f *Follower) FollowElection() (<-chan string, <-chan error, error) {
36 f.leaderCh = make(chan string)
37 f.errCh = make(chan error)
38
39 ch, err := f.client.Watch(f.key, f.stopCh)
40 if err != nil {
41 return nil, nil, err
42 }
43
44 go f.follow(ch)
45
46 return f.leaderCh, f.errCh, nil
47 }
48
49 // Stop stops monitoring an election.
50 func (f *Follower) Stop() {
51 close(f.stopCh)
52 }
53
54 func (f *Follower) follow(ch <-chan *store.KVPair) {
55 defer close(f.leaderCh)
56 defer close(f.errCh)
57
58 f.leader = ""
59 for kv := range ch {
60 if kv == nil {
61 continue
62 }
63 curr := string(kv.Value)
64 if curr == f.leader {
65 continue
66 }
67 f.leader = curr
68 f.leaderCh <- f.leader
69 }
70
71 // Channel closed, we return an error
72 f.errCh <- errors.New("Leader Election: watch leader channel closed, the store may be unavailable...")
73 }
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follower_test.go less more
0 package leadership
1
2 import (
3 "testing"
4
5 "github.com/docker/libkv/store"
6 libkvmock "github.com/docker/libkv/store/mock"
7 "github.com/stretchr/testify/assert"
8 "github.com/stretchr/testify/mock"
9 )
10
11 func TestFollower(t *testing.T) {
12 kv, err := libkvmock.New([]string{}, nil)
13 assert.NoError(t, err)
14 assert.NotNil(t, kv)
15
16 mockStore := kv.(*libkvmock.Mock)
17
18 kvCh := make(chan *store.KVPair)
19 var mockKVCh <-chan *store.KVPair = kvCh
20 mockStore.On("Watch", "test_key", mock.Anything).Return(mockKVCh, nil)
21
22 follower := NewFollower(kv, "test_key")
23 leaderCh, errCh, err := follower.FollowElection()
24 assert.Nil(t, err)
25
26 // Simulate leader updates
27 go func() {
28 kvCh <- &store.KVPair{Key: "test_key", Value: []byte("leader1")}
29 kvCh <- &store.KVPair{Key: "test_key", Value: []byte("leader1")}
30 kvCh <- &store.KVPair{Key: "test_key", Value: []byte("leader2")}
31 kvCh <- &store.KVPair{Key: "test_key", Value: []byte("leader1")}
32 }()
33
34 // We shouldn't see duplicate events.
35 assert.Equal(t, <-leaderCh, "leader1")
36 assert.Equal(t, <-leaderCh, "leader2")
37 assert.Equal(t, <-leaderCh, "leader1")
38 assert.Equal(t, follower.Leader(), "leader1")
39
40 // Once stopped, iteration over the leader channel should stop.
41 follower.Stop()
42 close(kvCh)
43
44 // Assert that we receive an error from the error chan to deal with the failover
45 err, open := <-errCh
46 assert.True(t, open)
47 assert.NotNil(t, err)
48
49 // Ensure that the chan is closed
50 _, open = <-leaderCh
51 assert.False(t, open)
52
53 mockStore.AssertExpectations(t)
54 }