README
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Leadership: Distributed Leader Election for Clustered Environments.
Leadership is a library for a cluster leader election on top of a distributed Key/Value store.
It's built using Swarm's pkg/store and is designed to work across multiple
storage backends.
You can use leadership with Consul, etcd and Zookeeper.
// Create a store using pkg/store.
client, err := store.NewStore("consul", []string{"127.0.0.1:8500"}, &store.Config{})
if err != nil {
panic(err)
}
underwood := leadership.NewCandidate(client, "service/swarm/leader", "underwood")
underwood.RunForElection()
electedCh := underwood.ElectedCh()
for isElected := range electedCh {
// This loop will run every time there is a change in our leadership
// status.
if isElected {
// We won the election - we are now the leader.
// Let's do leader stuff, for example, sleep for a while.
log.Printf("I won the election! I'm now the leader")
time.Sleep(10 * time.Second)
// Tired of being a leader? You can resign anytime.
candidate.Resign()
} else {
// We lost the election but are still running for leadership.
// `elected == false` is the default state and is the first event
// we'll receive from the channel. After a successful election,
// this event can get triggered if someone else steals the
// leadership or if we resign.
log.Printf("Lost the election, let's try another time")
}
}
It is possible to follow an election in real-time and get notified whenever there is a change in leadership:
follower := leadership.NewFollower(client, "service/swarm/leader")
follower.FollowElection()
leaderCh := follower.LeaderCh()
for leader := <-leaderCh {
// Leader is a string containing the value passed to `NewCandidate`.
log.Printf("%s is now the leader", leader)
}
A typical usecase for this is to be able to always send requests to the current leader.
Documentation
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Index ¶
Constants ¶
This section is empty.
Variables ¶
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Functions ¶
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Types ¶
type Candidate ¶
type Candidate struct {
// contains filtered or unexported fields
}
Candidate runs the leader election algorithm asynchronously
func NewCandidate ¶
NewCandidate creates a new Candidate
func (*Candidate) ElectedCh ¶
ElectedCh is used to get a channel which delivers signals on acquiring or losing leadership. It sends true if we become the leader, and false if we lose it.
func (*Candidate) Resign ¶
func (c *Candidate) Resign()
Resign forces the candidate to step-down and try again. If the candidate is not a leader, it doesn't have any effect. Candidate will retry immediately to acquire the leadership. If no-one else took it, then the Candidate will end up being a leader again.
func (*Candidate) RunForElection ¶
RunForElection starts the leader election algorithm. Updates in status are pushed through the ElectedCh channel.
type Follower ¶
type Follower struct {
// contains filtered or unexported fields
}
Follower can folow an election in real-time and push notifications whenever there is a change in leadership.
func NewFollower ¶
NewFollower creates a new follower.
func (*Follower) FollowElection ¶
FollowElection starts monitoring the election.
Source Files