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readme
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mike k
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README.md
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README.md
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README.md
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# Safe Redis Leader
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## Goal
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The Safe Redis Leader JS module is designed to provide a leader election implementation that provides tested gaurentees that there is only a single leader elected from a group of clients at one time.
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The implementation is a port of the stale [Redis Leader npm package](https://github.com/pierreinglebert/redis-leader) that implements a solution to the [known race condition](https://github.com/pierreinglebert/redis-leader/blob/c3b4db5df9802908728ad0ae4310a52e74acb462/index.js#L81). Additionally, this rewritten package:
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1. Removes the usage of `.bind` and `this`, as well as prototype inheritance (Without introducing classes in the main impl)
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2. Only exposes public api functions that should be exposed (no more public-but-should-be-private `_elect` fn)
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3. has a test suite within docker-compose using a real redis instance, which allows anyone to run the tests with no heavy dependency setup
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4. Has tests to assert the known race condition can no longer occur
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5. removes the need for `new`, by providing a simple `createSafeRedisLeader(...)` public fn
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6. Replace callback-hell with async/await
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## Usage
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Install the package:
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```bash
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npm install --save safe-redis-leader
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```
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in one terminal, run the follow index.js:
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```javascript
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const {createSafeRedisLeader} = require('safe-redis-leader')
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const Redis = require('ioredis')
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async function main(){
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const asyncRedis = new Redis({
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host: "locahost",
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port: 6379,
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password: "some-password"
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})
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const leaderElectionKey = 'the-election'
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const safeLeader = await createSafeRedisLeader({
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asyncRedis: asyncRedis,
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ttl: 1500,
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wait: 3000,
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key: leaderElectionKey
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})
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safeLeader.on("elected", ()=>{
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console.log("I'm the leader - 1")
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})
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await safeLeader.elect()
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}
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main().catch((e)=>{
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console.error(e)
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process.exit(1)
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})
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```
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In a seperate terminal/tab, run the following index.js:
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```javascript
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const {createSafeRedisLeader} = require('safe-redis-leader')
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const Redis = require('ioredis')
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async function main(){
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const asyncRedis = new Redis({
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host: "locahost",
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port: 6379,
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password: "some-password"
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})
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const leaderElectionKey = 'the-election'
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const safeLeader = await createSafeRedisLeader({
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asyncRedis: asyncRedis,
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ttl: 1500,
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wait: 3000,
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key: leaderElectionKey
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})
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safeLeader.on("elected", ()=>{
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console.log("I'm the leader - 2")
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})
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await safeLeader.elect()
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}
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main().catch((e)=>{
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console.error(e)
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process.exit(1)
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})
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```
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## Run Library Tests
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npm run docker:test
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# License
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MIT
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@@ -2,7 +2,7 @@
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"name": "safe-redis-leader",
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"version": "0.0.1",
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"description": "Redis leader election implementation that does not have any race conditions",
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"main": "index.js",
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"main": "src/src/index.js",
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"scripts": {
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"test": "npm install && node ./docker/scripts/runner.js"
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},
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@@ -107,87 +107,4 @@ async function createSafeRedisLeader({
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}
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module.exports.createSafeRedisLeader = createSafeRedisLeader
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// function Leader(redis, options) {
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// options = options || {};
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// this.id = uuid.v4();
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// this.redis = redis;
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// this.options = {};
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// this.options.ttl = options.ttl || 10000; // Lock time to live in milliseconds
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// this.options.wait = options.wait || 1000; // time between 2 tries to get lock
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// this.key = hashKey(options.key || 'default');
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// }
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// util.inherits(Leader, EventEmitter);
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// /**
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// * Renew leader as elected
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// */
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// Leader.prototype._renew = function _renew() {
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// // it is safer to check we are still leader
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// this.isLeader(function(err, isLeader) {
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// if(isLeader) {
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// this.redis.pexpire(this.key, this.options.ttl, function(err) {
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// if(err) {
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// this.emit('error', err);
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// }
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// }.bind(this));
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// } else {
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// clearInterval(this.renewId);
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// this.electId = setTimeout(Leader.prototype.elect.bind(this), this.options.wait);
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// this.emit('revoked');
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// }
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// }.bind(this));
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// };
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// /**
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// * Try to get elected as leader
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// */
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// Leader.prototype.elect = function elect() {
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// // atomic redis set
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// this.redis.set(this.key, this.id, 'PX', this.options.ttl, 'NX', function(err, res) {
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// if(err) {
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// return this.emit('error', err);
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// }
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// if(res !== null) {
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// this.emit('elected');
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// this.renewId = setInterval(Leader.prototype._renew.bind(this), this.options.ttl / 2);
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// } else {
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// // use setTimeout to avoid max call stack error
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// this.electId = setTimeout(Leader.prototype.elect.bind(this), this.options.wait);
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// }
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// }.bind(this));
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// };
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// Leader.prototype.isLeader = function isLeader(done) {
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// this.redis.get(this.key, function(err, id) {
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// if(err) {
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// return done(err);
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// }
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// done(null, (id === this.id));
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// }.bind(this));
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// };
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// /**
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// * if leader, stop being a leader
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// * stop trying to be a leader
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// */
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// Leader.prototype.stop = function stop() {
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// this.isLeader(function(err, isLeader) {
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// if(isLeader) {
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// // possible race condition, cause we need atomicity on get -> isEqual -> delete
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// this.redis.del(this.key, function(err) {
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// if(err) {
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// return this.emit('error', err);
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// }
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// this.emit('revoked');
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// }.bind(this));
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// }
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// clearInterval(this.renewId);
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// clearTimeout(this.electId);
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// }.bind(this));
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// };
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// module.exports = Leader;
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module.exports.createSafeRedisLeader = createSafeRedisLeader
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