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Author | SHA1 | Date |
---|---|---|
Vitaliy Filippov | dfa8262e4c | |
Vitaliy Filippov | 9674117da7 | |
Vitaliy Filippov | 5b4444eb65 | |
Vitaliy Filippov | 58cf308112 | |
Vitaliy Filippov | 669d755381 |
|
@ -0,0 +1,103 @@
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# TinyRaft
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Raft leader election isolated from the rest of the algorithm.
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TinyRaft doesn't know anything about replication and doesn't require you to
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implement it.
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Actual network communication is also abstracted away and hidden behind a simple
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callback interface.
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The only task of TinyRaft is to elect the leader and guarantee that there is
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only one leader at each moment.
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TinyRaft can be used:
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- As a simple leader election algorithm without replication at all
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- As a building block for the standard Raft algorithm if you add log replication
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- For other variations of "weaker consensus" if you add another method of replication
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Some replication ideas for you:
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- Log-less replication: Add a version number for each key in the database
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and make the leader synchronize follower databases by simply dumping all
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followers' databases with the newest term (followers with older terms should
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be ignored), comparing version numbers and making the newest version of each
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key win.
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- Erasure coding: Suppose you store large values. You can split each value into
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N parts, add K parity parts to it using Reed-Solomon codes (ISA-L/jerasure)
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and store them on different nodes in the form of Raft-like logs or similar
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to the log-less replication with version numbers, and make master synchronize
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followers by reconstructing every original value.
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## Example Application
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TODO: Extract and describe Antietcd.
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## Usage
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```js
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const node = new TinyRaft({
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nodes: [ 1, 2, 3 ],
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nodeId: 1,
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electionTimeout: 5000,
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heartbeatTimeout: 1000,
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leadershipTimeout: 10000,
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initialTerm: 0,
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leaderPriority: 0,
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send: function(to, msg)
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{
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// Function to send message <msg> to node with ID <to>
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// msg.type is one of TinyRaft.VOTE_REQUEST, TinyRaft.VOTE, TinyRaft.PING, TinyRaft.PONG
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// msg.leader is the leader ID or null
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// msg.term is the term number
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// msg.priority is the optional leadership priority if set in config
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},
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});
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// Watch for election state
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node.on('change', (st) =>
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{
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console.log(
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'node '+node.nodeId+': '+(st.state == TinyRaft.FOLLOWER ? 'following '+st.leader : st.state)+
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', term '+st.term+(st.state == TinyRaft.LEADER ? ', followers: '+st.followers.join(', ') : '')
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);
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});
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// Start Raft node or start a new election round
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node.start();
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// Optional; may be called for a follower when it receives a message from a live leader,
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// for example, a replication message, and causes the follower to move its round expiration forward
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node.markAlive();
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// Update cluster node list
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node.setNodes([ 1, 2, 3 ]);
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// Incoming messages should be fed to TinyRaft like this (from = ID of the sender):
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node.onReceive(from, msg);
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// Stop Raft node
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node.stop();
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```
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## Additional features
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### Leader expiration
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Supports leader expiration like in NuRaft:
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https://github.com/eBay/NuRaft/blob/master/docs/leadership_expiration.md
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When leader expiration is enabled, followers respond to leader heartbeats
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(pings) with "pong" messages and if the leader doesn't receive a quorum of
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replies in leadershipTimeout - it starts a new round of voting.
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### Leadership priorities
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Also supports leader priorities, similar to NuRaft but even simpler:
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if a node receives a VoteRequest message with larger term but with smaller
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priority than its own, it immediately starts a new voting round.
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It guarantees that a node with non-maximum priority can't become leader
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without being re-elected.
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If all priorities are equal (or just zero), the election algorithm
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becomes identical to the basic algorithm without priorities.
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@ -0,0 +1,44 @@
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// Fake timer for node.js which _guarantees_ that all asynchronous timer
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// callbacks are called during a tested period
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function FakeTimer(startTime)
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{
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this.time = Number(startTime)||0;
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this.timers = [];
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this.id = 0;
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this.setTimeout = (func, ms) =>
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{
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this.timers.push({ id: ++this.id, func, at: this.time+ms });
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return this.id;
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};
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this.setInterval = (func, ms) =>
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{
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this.timers.push({ id: ++this.id, func, at: this.time+ms, repeat: ms });
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return this.id;
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};
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this.clearInterval = this.clearTimeout = (id) =>
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{
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this.timers = this.timers.filter(t => t.id != id);
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};
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this.setImmediate = (func) => this.setTimeout(func, 0);
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this.runFor = async (ms) =>
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{
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const end = this.time+ms;
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this.timers.sort((a, b) => a.at - b.at);
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while (this.timers.length && this.timers[0].at <= end)
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{
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const { func, at, repeat } = this.timers[0];
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if (!repeat)
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this.timers.shift();
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else
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this.timers[0].at += repeat;
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if (at > this.time)
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this.time = at;
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func();
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this.timers.sort((a, b) => a.at - b.at);
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}
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this.time = end;
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};
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}
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module.exports = FakeTimer;
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34
tinyraft.js
34
tinyraft.js
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@ -62,18 +62,19 @@ class TinyRaft extends EventEmitter
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this.term = 0;
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this.state = null;
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this.leader = null;
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this.confirmed = {};
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}
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_nextTerm(after)
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{
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if (this.electionTimer)
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{
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clearTimeout(this.electionTimer);
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TinyRaft.clearTimeout(this.electionTimer);
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this.electionTimer = null;
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}
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if (after >= 0)
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{
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this.electionTimer = setTimeout(() => this.start(), after + this.randomTimeout * Math.random());
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this.electionTimer = TinyRaft.setTimeout(() => this.start(), after + this.randomTimeout * Math.random());
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}
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}
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@ -86,10 +87,11 @@ class TinyRaft extends EventEmitter
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this.votes = { [this.nodeId]: [ this.nodeId ] };
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this.state = CANDIDATE;
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this.followers = null;
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this.confirmed = {};
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this.leader = this.nodeId;
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if (!this.heartbeatTimer)
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{
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this.heartbeatTimer = setInterval(() => this._heartbeat(), this.heartbeatTimeout);
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this.heartbeatTimer = TinyRaft.setInterval(() => this._heartbeat(), this.heartbeatTimeout);
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}
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for (const node of this.nodes)
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{
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@ -107,12 +109,12 @@ class TinyRaft extends EventEmitter
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{
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if (this.electionTimer)
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{
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clearTimeout(this.electionTimer);
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TinyRaft.clearTimeout(this.electionTimer);
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this.electionTimer = null;
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}
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if (this.heartbeatTimer)
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{
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clearTimeout(this.heartbeatTimer);
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TinyRaft.clearInterval(this.heartbeatTimer);
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this.heartbeatTimer = null;
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}
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}
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@ -121,6 +123,7 @@ class TinyRaft extends EventEmitter
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{
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if (this.state == LEADER)
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{
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this.confirmed = {};
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for (const node of (this.leadershipTimeout ? this.followers : this.nodes))
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{
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if (node != this.nodeId)
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@ -165,6 +168,8 @@ class TinyRaft extends EventEmitter
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this.leader = msg.leader;
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this.term = msg.term;
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this.state = CANDIDATE;
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this.followers = null;
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this.confirmed = {};
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this._nextTerm(this.heartbeatTimeout*2 + this.electionTimeout);
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this.emit('change', { state: this.state, term: this.term, leader: this.leader });
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}
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@ -184,6 +189,7 @@ class TinyRaft extends EventEmitter
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this.term = msg.term;
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this.state = FOLLOWER;
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this.followers = null;
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this.confirmed = {};
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this.leader = msg.leader;
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this.votes = {};
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this.emit('change', { state: this.state, term: this.term, leader: this.leader });
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@ -214,6 +220,7 @@ class TinyRaft extends EventEmitter
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{
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this.leader = msg.leader;
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this.state = LEADER;
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this.confirmed = {};
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this._nextTerm(this.leadershipTimeout > 0 ? this.leadershipTimeout : -1);
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this.followers = this.votes[this.nodeId];
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// Send a heartbeat to confirm leadership
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@ -249,7 +256,7 @@ class TinyRaft extends EventEmitter
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{
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this.markAlive();
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}
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if (this.leadershipTimeout > 0)
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if (this.leadershipTimeout > 0 || this.state == FOLLOWER && from != this.leader)
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{
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this.send(from, { type: PONG, term: this.term, leader: this.leader });
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}
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@ -261,13 +268,18 @@ class TinyRaft extends EventEmitter
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{
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return;
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}
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if (msg.leader != this.nodeId)
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if (msg.leader != this.nodeId || msg.term != this.term)
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{
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this.start();
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}
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else
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else if (this.leadershipTimeout > 0)
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{
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this._nextTerm(this.leadershipTimeout > 0 ? this.leadershipTimeout : -1);
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this.confirmed[from] = true;
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if (Object.keys(this.confirmed).length >= (1 + (0 | this.nodes.length/2)))
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{
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// We have quorum
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this._nextTerm(this.leadershipTimeout);
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}
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}
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}
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@ -311,6 +323,10 @@ class TinyRaft extends EventEmitter
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}
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}
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TinyRaft.setTimeout = setTimeout;
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TinyRaft.clearTimeout = clearTimeout;
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TinyRaft.setInterval = setInterval;
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TinyRaft.clearInterval = clearInterval;
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TinyRaft.VOTE_REQUEST = VOTE_REQUEST;
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TinyRaft.VOTE = VOTE;
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TinyRaft.PING = PING;
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|
|
102
tinyraft.spec.js
102
tinyraft.spec.js
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@ -1,4 +1,11 @@
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const TinyRaft = require('./tinyraft.js');
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const FakeTimer = require('./faketimer.js');
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const fake = new FakeTimer();
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TinyRaft.setTimeout = fake.setTimeout;
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TinyRaft.clearTimeout = fake.clearTimeout;
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TinyRaft.setInterval = fake.setInterval;
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TinyRaft.clearInterval = fake.clearInterval;
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function newNode(id, nodes, partitions, mod)
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{
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@ -12,8 +19,8 @@ function newNode(id, nodes, partitions, mod)
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{
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if (!partitions[n.nodeId+'-'+to] && !partitions[to+'-'+n.nodeId] && nodes[to])
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{
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console.log('received from '+n.nodeId+' to '+to+': '+JSON.stringify(msg));
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setImmediate(function() { nodes[to].onReceive(n.nodeId, msg); });
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console.log('['+fake.time+'] received from '+n.nodeId+' to '+to+': '+JSON.stringify(msg));
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fake.setImmediate(function() { nodes[to].onReceive(n.nodeId, msg); });
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}
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},
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};
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@ -23,7 +30,7 @@ function newNode(id, nodes, partitions, mod)
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n.on('change', (st) =>
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{
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console.log(
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'node '+n.nodeId+': '+(st.state == TinyRaft.FOLLOWER ? 'following '+st.leader : st.state)+
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'['+fake.time+'] node '+n.nodeId+': '+(st.state == TinyRaft.FOLLOWER ? 'following '+st.leader : st.state)+
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', term '+st.term+(st.state == TinyRaft.LEADER ? ', followers: '+st.followers.join(', ') : '')
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);
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});
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@ -48,6 +55,7 @@ function newNodes(count, partitions, mod)
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function checkQuorum(nodes, count)
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{
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let leaders = 0;
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let out = 0;
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for (const i in nodes)
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{
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if (nodes[i].state == TinyRaft.LEADER)
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|
@ -58,14 +66,16 @@ function checkQuorum(nodes, count)
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}
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else if (nodes[i].state != TinyRaft.FOLLOWER)
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{
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throw new Error('node '+i+' is not in quorum: state '+nodes[i].state);
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out++;
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if (out > nodes.length-count)
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throw new Error('node '+i+' is not in quorum: state '+nodes[i].state);
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}
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}
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if (leaders != 1)
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{
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throw new Error('we have '+leaders+' leaders instead of exactly 1');
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}
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console.log('OK: '+count+' nodes in quorum');
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console.log('['+fake.time+'] OK: '+count+' nodes in quorum');
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}
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function checkNoQuorum(nodes)
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|
@ -75,11 +85,12 @@ function checkNoQuorum(nodes)
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{
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throw new Error('we have non-candidates ('+nc.map(n => n.nodeId).join(', ')+'), but we should not');
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}
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console.log('OK: '+Object.keys(nodes).length+' candidates, no quorum');
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console.log('['+fake.time+'] OK: '+Object.keys(nodes).length+' candidates, no quorum');
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}
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async function testStartThenRemoveNode()
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{
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console.log('--------------------------------------------------------------------------------');
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console.log('testStartThenRemoveNode');
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const nodes = newNodes(5);
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let leaderChanges = 0, prevLeader = null;
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|
@ -91,7 +102,7 @@ async function testStartThenRemoveNode()
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leaderChanges++;
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}
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});
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await new Promise(ok => setTimeout(ok, 2000));
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await fake.runFor(2000);
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checkQuorum(nodes, 5);
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if (leaderChanges >= 3)
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{
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|
@ -103,7 +114,7 @@ async function testStartThenRemoveNode()
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nodes[leader].stop();
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delete nodes[leader];
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// Check quorum after 2000ms
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await new Promise(ok => setTimeout(ok, 2000));
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await fake.runFor(2000);
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checkQuorum(nodes, 4);
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// Stop the leader again
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leader = nodes[Object.keys(nodes)[0]].leader;
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|
@ -111,7 +122,7 @@ async function testStartThenRemoveNode()
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nodes[leader].stop();
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delete nodes[leader];
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// Check quorum after 2000ms
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await new Promise(ok => setTimeout(ok, 2000));
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await fake.runFor(2000);
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checkQuorum(nodes, 3);
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// Stop the leader again
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leader = nodes[Object.keys(nodes)[0]].leader;
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|
@ -119,7 +130,7 @@ async function testStartThenRemoveNode()
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nodes[leader].stop();
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delete nodes[leader];
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// Check that no quorum exists
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await new Promise(ok => setTimeout(ok, 2000));
|
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await fake.runFor(2000);
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checkNoQuorum(nodes);
|
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// Clean up
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||||
for (const id in nodes)
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|
@ -131,9 +142,10 @@ async function testStartThenRemoveNode()
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|||
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async function testAddNode()
|
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{
|
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console.log('--------------------------------------------------------------------------------');
|
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console.log('testAddNode');
|
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const nodes = newNodes(5, {}, cfg => cfg.initialTerm = 1000);
|
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await new Promise(ok => setTimeout(ok, 2000));
|
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await fake.runFor(2000);
|
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checkQuorum(nodes, 5);
|
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// Add node
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newNode(6, nodes);
|
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|
@ -141,7 +153,7 @@ async function testAddNode()
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nodes[i].setNodes([ 1, 2, 3, 4, 5, 6 ]);
|
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nodes[6].start();
|
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// Check quorum after 2000ms
|
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await new Promise(ok => setTimeout(ok, 2000));
|
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await fake.runFor(2000);
|
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checkQuorum(nodes, 6);
|
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// Clean up
|
||||
for (const id in nodes)
|
||||
|
@ -153,22 +165,23 @@ async function testAddNode()
|
|||
|
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async function testLeadershipExpiration()
|
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{
|
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console.log('--------------------------------------------------------------------------------');
|
||||
console.log('testLeadershipExpiration');
|
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const partitions = {};
|
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const nodes = newNodes(5, partitions, cfg => cfg.leadershipTimeout = 1500);
|
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// Check that 5 nodes are in quorum after 2000ms
|
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await new Promise(ok => setTimeout(ok, 2000));
|
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await fake.runFor(2000);
|
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checkQuorum(nodes, 5);
|
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// Break network on the leader
|
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let leader = nodes[1].leader;
|
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console.log("stopping the leader's ("+leader+") network");
|
||||
console.log("["+fake.time+"] --> stopping the leader's ("+leader+") network");
|
||||
for (let i = 1; i <= 5; i++)
|
||||
{
|
||||
partitions[i+'-'+leader] = true;
|
||||
partitions[leader+'-'+i] = true;
|
||||
}
|
||||
// Check that the leader loses leadership after 2 * leadershipTimeout
|
||||
await new Promise(ok => setTimeout(ok, 3000));
|
||||
await fake.runFor(3000);
|
||||
if (nodes[leader].state != TinyRaft.CANDIDATE)
|
||||
{
|
||||
throw new Error("leadership expiration doesn't work");
|
||||
|
@ -183,6 +196,7 @@ async function testLeadershipExpiration()
|
|||
|
||||
async function testRestart()
|
||||
{
|
||||
console.log('--------------------------------------------------------------------------------');
|
||||
console.log('testRestart');
|
||||
const nodes = newNodes(5, {}, cfg => cfg.initialTerm = 1000);
|
||||
let leaderChanges = 0, prevLeader = null;
|
||||
|
@ -196,7 +210,7 @@ async function testRestart()
|
|||
}
|
||||
});
|
||||
// Check that 5 nodes are in quorum after 2000ms
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 5);
|
||||
if (leaderChanges >= 3)
|
||||
{
|
||||
|
@ -208,18 +222,18 @@ async function testRestart()
|
|||
{
|
||||
restarted = 1 + (prevLeader + 1) % 5;
|
||||
}
|
||||
console.log("stopping a follower (node "+restarted+")");
|
||||
console.log("["+fake.time+"] --> stopping a follower (node "+restarted+")");
|
||||
nodes[restarted].stop();
|
||||
delete nodes[restarted];
|
||||
// Wait 2000ms
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
// Restart a follower
|
||||
console.log("restarting a follower (node "+restarted+")");
|
||||
console.log("["+fake.time+"] --> restarting a follower (node "+restarted+")");
|
||||
leaderChanges = 0;
|
||||
newNode(restarted, nodes, {}, null);
|
||||
nodes[restarted].start();
|
||||
// Check quorum and the fact that the leader didn't change after 2000ms
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 5);
|
||||
if (leaderChanges > 0)
|
||||
{
|
||||
|
@ -235,20 +249,21 @@ async function testRestart()
|
|||
|
||||
async function testChangeNodes()
|
||||
{
|
||||
console.log('--------------------------------------------------------------------------------');
|
||||
console.log('testChangeNodes');
|
||||
console.log('starting nodes 1-5');
|
||||
console.log('['+fake.time+'] --> starting nodes 1-5');
|
||||
const nodes = newNodes(5, {}, cfg => cfg.initialTerm = 1000);
|
||||
// Check that 5 nodes are in quorum after 2000ms
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 5);
|
||||
// Stop node 4
|
||||
console.log('stopping node 4');
|
||||
console.log('['+fake.time+'] --> stopping node 4');
|
||||
nodes[4].stop();
|
||||
delete nodes[4];
|
||||
// Wait 1000ms
|
||||
await new Promise(ok => setTimeout(ok, 1000));
|
||||
await fake.runFor(1000);
|
||||
// Change nodes from 1 2 3 4 5 to 1 2 3 5 6
|
||||
console.log('starting node 6');
|
||||
console.log('['+fake.time+'] --> starting node 6');
|
||||
newNode(6, nodes);
|
||||
nodes[6].start();
|
||||
nodes[1].setNodes([ 1, 2, 3, 5, 6 ]);
|
||||
|
@ -257,7 +272,7 @@ async function testChangeNodes()
|
|||
nodes[5].setNodes([ 1, 2, 3, 5, 6 ]);
|
||||
nodes[6].setNodes([ 1, 2, 3, 5, 6 ]);
|
||||
// Check that 5 nodes are in quorum after 2000ms
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 5);
|
||||
// Clean up
|
||||
for (const id in nodes)
|
||||
|
@ -270,33 +285,34 @@ async function testChangeNodes()
|
|||
|
||||
async function testLeaderPriority()
|
||||
{
|
||||
console.log('--------------------------------------------------------------------------------');
|
||||
console.log('testLeaderPriority');
|
||||
console.log('starting nodes 1-5');
|
||||
console.log('['+fake.time+'] --> starting nodes 1-5');
|
||||
const nodes = newNodes(5, {}, cfg => cfg.leaderPriority = cfg.nodeId+1);
|
||||
// Check that 5 nodes are in quorum after 2000ms
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 5);
|
||||
if (nodes[1].leader != 5)
|
||||
{
|
||||
throw new Error('leader is not 5');
|
||||
}
|
||||
// Stop node 5
|
||||
console.log('stopping node 5');
|
||||
console.log('['+fake.time+'] --> stopping node 5');
|
||||
nodes[5].stop();
|
||||
delete nodes[5];
|
||||
// Wait 2000ms and check that the leader is now 4
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 4);
|
||||
if (nodes[1].leader != 4)
|
||||
{
|
||||
throw new Error('leader is not 4');
|
||||
}
|
||||
// Stop node 4
|
||||
console.log('stopping node 4');
|
||||
console.log('['+fake.time+'] --> stopping node 4');
|
||||
nodes[4].stop();
|
||||
delete nodes[4];
|
||||
// Wait 2000ms and check that the leader is now 3
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
await fake.runFor(2000);
|
||||
checkQuorum(nodes, 3);
|
||||
if (nodes[1].leader != 3)
|
||||
{
|
||||
|
@ -313,6 +329,7 @@ async function testLeaderPriority()
|
|||
|
||||
async function testPartition1_3()
|
||||
{
|
||||
console.log('--------------------------------------------------------------------------------');
|
||||
console.log('testPartition1_3');
|
||||
const partitions = { '1-3': true, '3-1': true };
|
||||
const nodes = newNodes(3, partitions, cfg => cfg.nodes = [ 1, 2, 3 ]);
|
||||
|
@ -325,24 +342,19 @@ async function testPartition1_3()
|
|||
leaderChanges++;
|
||||
}
|
||||
});
|
||||
// Check that 3 nodes are in quorum after 2000ms
|
||||
// 2 is always elected as leader because it's the first node that can determine
|
||||
// that the first voting round has failed: it receives a vote for 1 from 1 and
|
||||
// a vote for 3 from 3. So it knows that no node can get 2 votes. 1 and 3, at
|
||||
// the same time, don't know it for sure because they don't receive failures
|
||||
// from each other due to the network partition.
|
||||
await new Promise(ok => setTimeout(ok, 2000));
|
||||
checkQuorum(nodes, 3);
|
||||
if (leaderChanges >= 3)
|
||||
{
|
||||
throw new Error('More than 3 leader changes in 2000ms: '+leaderChanges);
|
||||
}
|
||||
// Check that 2 or 3 nodes are in quorum after 5000ms
|
||||
// This situation should be fixed by "prevote protocol", but it breaks other things
|
||||
await fake.runFor(5000);
|
||||
if (nodes[2].leader == 2)
|
||||
checkQuorum(nodes, 3);
|
||||
else
|
||||
checkQuorum(nodes, 2);
|
||||
// Clean up
|
||||
for (const id in nodes)
|
||||
{
|
||||
nodes[id].stop();
|
||||
}
|
||||
console.log('testLeadershipExpiration: OK');
|
||||
console.log('testPartition1_3: OK');
|
||||
}
|
||||
|
||||
async function run()
|
||||
|
|
Loading…
Reference in New Issue