node-raft-redis/lib/esm/index.js

Consensus for node microservices, based on a simplified version of the [raft algorithm](https://raft.github.io/). Requires redis as a medium. Features automatic discovery of the services of same kind. Selects one instance of a microservice as leader. For

import { createClient } from "redis";
import { EventEmitter } from "events";
const randomTimeout = () => {
    const min = 1000;
    const max = 1500;
    return Math.floor(Math.random() * (max - min + 1)) + min;
};
const randomString = () => {
    return (Math.random().toString(36).substring(2, 15) +
        Math.random().toString(36).substring(2, 15));
};
export class Candidate extends EventEmitter {
    kind = "";
    __meta = {};
    running = false;
    __instanceId = randomString();
    redisClient;
    subscriptionClient = null;
    leaderSubscription = false;
    followerSubscription = false;
    privateSubsciption = false;
    votes = new Set();
    votedFor = "";
    __currentTerm = 1;
    __state = "follower";
    timeout = null;
    requestInterval = null;
    leadershipInterval = null;
    countNodesInterval = null;
    stopCheckInterval = null;
    startCheckInterval = null;
    constructor(options) {
        super();
        const { redis, kind, meta } = options;
        this.kind = kind || "";
        this.__meta = meta || "";
        if (redis.url) {
            this.redisClient = createClient({ url: redis.url });
        }
        else {
            this.redisClient = createClient({
                socket: {
                    host: redis.host,
                    port: redis.port,
                },
            });
        }
        this.redisClient.on("error", (err) => {
            this.emit("error", err);
        });
    }
    keepAlive() {
        return this.redisClient.set(`consensus-nodes:${this.kind}:${this.__instanceId}`, JSON.stringify({ ts: Date.now(), meta: this.__meta, state: this.__state }));
    }
    async getInstanceCount() {
        return this.getInstances().then((instances) => instances.length);
    }
    async getInstances() {
        const keys = await this.redisClient.keys(`consensus-nodes:${this.kind}:*`);
        const alive = [];
        const dead = [];
        for (const key of keys) {
            const val = await this.redisClient.get(key);
            if (!val) {
                dead.push(key);
                continue;
            }
            const { ts, meta, state } = JSON.parse(val);
            if (Date.now() - parseInt(ts, 10) > 2000) {
                dead.push(key);
            }
            else {
                const instanceId = key.split(":")[2];
                const instance = {
                    id: instanceId,
                    meta,
                    state,
                };
                alive.push(instance);
            }
        }
        if (dead.length) {
            await this.redisClient.del(dead);
        }
        return alive;
    }
    async startTimeout() {
        this.votes = new Set();
        if (this.timeout) {
            clearInterval(this.timeout);
        }
        if (this.leadershipInterval) {
            clearInterval(this.leadershipInterval);
        }
        if (this.requestInterval) {
            clearInterval(this.requestInterval);
            this.requestInterval = null;
        }
        this.timeout = setInterval(() => {
            this.setState("candidate");
            this.__currentTerm++;
            this.votedFor = this.__instanceId;
            this.votes.add(this.__instanceId);
            const sendRequest = () => {
                const message = {
                    type: "request",
                    from: this.__instanceId,
                    currentTerm: this.__currentTerm,
                    ignore: [...this.votes],
                };
                this.redisClient.publish(`consensus-events:${this.kind}`, JSON.stringify(message));
            };
            this.requestInterval ??= setInterval(() => {
                sendRequest();
            }, 400);
            sendRequest();
        }, randomTimeout());
    }
    startLeadership() {
        if (this.timeout) {
            clearInterval(this.timeout);
        }
        if (this.leadershipInterval) {
            clearInterval(this.leadershipInterval);
        }
        if (this.requestInterval) {
            clearInterval(this.requestInterval);
        }
        const _message = {
            type: "check",
            from: this.__instanceId,
            currentTerm: this.__currentTerm,
        };
        this.redisClient.publish(`consensus-events:${this.kind}`, JSON.stringify(_message));
        this.leadershipInterval = setInterval(() => {
            this.redisClient.publish(`consensus-events:${this.kind}`, JSON.stringify(_message));
        }, 400);
        this.setState("leader");
    }
    setState(state, initiator) {
        if (state !== "leader") {
            if (this.leadershipInterval) {
                clearInterval(this.leadershipInterval);
            }
        }
        if (state !== "candidate") {
            this.emit("__init");
        }
        if (this.__state !== state) {
            this.__state = state;
            this.keepAlive();
            if (state === "leader") {
                this.subscribeLeaderChannel();
                this.emit("elected");
            }
            else {
                this.unsubscribeLeaderChannel();
            }
            if (state === "follower") {
                this.subscribeFollowerChannel();
                this.emit("defeated", initiator);
            }
            else {
                this.unsubscribeFollowerChannel();
            }
            this.emit("statechange", state);
        }
    }
    async _stop() {
        try {
            if (this.timeout) {
                clearInterval(this.timeout);
            }
            if (this.leadershipInterval) {
                clearInterval(this.leadershipInterval);
            }
            if (this.countNodesInterval) {
                clearInterval(this.countNodesInterval);
            }
            if (this.subscriptionClient?.isOpen) {
                await this.subscriptionClient.unsubscribe();
                await this.subscriptionClient.quit();
            }
            if (this.redisClient?.isOpen) {
                await this.redisClient.quit();
            }
            this.running = false;
        }
        catch (error) {
            this.emit("error", error);
        }
    }
    async subscribePrivateChannel() {
        if (this.privateSubsciption) {
            return;
        }
        this.privateSubsciption = true;
        await this.subscriptionClient?.subscribe(`consensus-messages:${this.kind}:${this.__instanceId}`, (str) => {
            const { message, from, fromLeader } = JSON.parse(str);
            if (from !== this.__instanceId) {
                this.emit("message", { message, from });
                if (this.state === "leader") {
                    this.emit("message:from:follower", { message, from });
                }
                if (fromLeader) {
                    this.emit("message:from:leader", { message, from });
                }
            }
        });
    }
    async unsubscribePrivateChannel() {
        await this.subscriptionClient?.unsubscribe(`consensus-messages:${this.kind}:${this.__instanceId}`);
        this.privateSubsciption = false;
    }
    async subscribeFollowerChannel() {
        if (this.followerSubscription) {
            return;
        }
        this.followerSubscription = true;
        await this.subscriptionClient?.subscribe(`consensus-messages:${this.kind}:followers`, (str) => {
            const { message, from, fromLeader } = JSON.parse(str);
            if (this.__state === "follower" && from !== this.__instanceId) {
                this.emit("message", { message, from });
                if (fromLeader) {
                    this.emit("message:from:leader", { message, from });
                }
            }
        });
    }
    async unsubscribeFollowerChannel() {
        await this.subscriptionClient?.unsubscribe(`consensus-messages:${this.kind}:followers`);
        this.followerSubscription = false;
    }
    async subscribeLeaderChannel() {
        if (this.leaderSubscription) {
            return;
        }
        this.leaderSubscription = true;
        await this.subscriptionClient?.subscribe(`consensus-messages:${this.kind}:leader`, (str) => {
            const { message, from } = JSON.parse(str);
            if (this.__state === "leader" && from !== this.__instanceId) {
                this.emit("message", { message, from });
                this.emit("message:from:follower", { message, from });
            }
        });
    }
    async unsubscribeLeaderChannel() {
        await this.subscriptionClient?.unsubscribe(`consensus-messages:${this.kind}:leader`);
        this.leaderSubscription = false;
    }
    async _start() {
        this.running = true;
        await this.redisClient.connect();
        await new Promise((r) => setTimeout(r, randomTimeout()));
        await this.keepAlive();
        await new Promise((r) => setTimeout(r, 1000));
        await this.keepAlive();
        let count = await this.getInstanceCount();
        this.countNodesInterval = setInterval(async () => {
            await this.keepAlive();
            count = await this.getInstanceCount();
            if (count === 1 && this.__state !== "leader") {
                this.startLeadership();
            }
        }, 1000);
        this.subscriptionClient = this.redisClient.duplicate();
        this.subscriptionClient.on("error", (err) => {
            this.emit("error", err);
        });
        this.subscribeFollowerChannel();
        this.subscribePrivateChannel();
        this.subscriptionClient.subscribe(`consensus-messages:${this.kind}`, (str) => {
            const { message, from, fromLeader } = JSON.parse(str);
            if (from !== this.__instanceId) {
                this.emit("message", { message, from });
                if (fromLeader) {
                    this.emit("message:from:leader", { message, from });
                }
            }
        });
        this.subscriptionClient.subscribe(`consensus-events:${this.kind}`, (str) => {
            const message = JSON.parse(str);
            if (message.from === this.__instanceId ||
                message.ignore?.includes(this.__instanceId)) {
                return;
            }
            if (message.type === "request" || message.type === "check") {
                if (this.__currentTerm < message.currentTerm ||
                    (message.type === "check" &&
                        this.__currentTerm <= message.currentTerm)) {
                    if (this.leadershipInterval) {
                        clearInterval(this.leadershipInterval);
                    }
                    this.__currentTerm = message.currentTerm;
                    this.votedFor = message.from;
                    this.setState("follower", message.from);
                    const reply = {
                        type: "vote",
                        from: this.__instanceId,
                        to: message.from,
                        granted: true,
                        currentTerm: this.__currentTerm,
                    };
                    this.redisClient.publish(`consensus-events:${this.kind}`, JSON.stringify(reply));
                    this.startTimeout();
                }
                else {
                    const reply = {
                        type: "vote",
                        from: this.__instanceId,
                        to: message.from,
                        granted: false,
                        currentTerm: this.__currentTerm,
                    };
                    this.redisClient.publish(`consensus-events:${this.kind}`, JSON.stringify(reply));
                }
            }
            else {
                if (this.__state === "candidate" &&
                    message.to === this.__instanceId &&
                    message.granted &&
                    message.currentTerm === this.__currentTerm) {
                    this.votes.add(message.from);
                    if (this.votes.size >= Math.floor(count / 2) + 1) {
                        this.startLeadership();
                    }
                }
            }
        });
        await this.subscriptionClient.connect();
        this.startTimeout();
        await new Promise((resolve) => {
            this.once("__init", resolve);
        });
    }
    async start() {
        if (this.startCheckInterval) {
            clearInterval(this.startCheckInterval);
        }
        if (this.stopCheckInterval) {
            clearInterval(this.stopCheckInterval);
        }
        if (this.running) {
            return;
        }
        return new Promise((resolve) => {
            this.startCheckInterval = setInterval(async () => {
                if (!this.redisClient.isOpen &&
                    !this.subscriptionClient?.isOpen &&
                    !this.running) {
                    if (this.startCheckInterval) {
                        clearInterval(this.startCheckInterval);
                    }
                    await this._start();
                    resolve();
                }
            }, 100);
        });
    }
    async stop() {
        if (this.startCheckInterval) {
            clearInterval(this.startCheckInterval);
            if (!this.running) {
                return;
            }
        }
        if (this.stopCheckInterval) {
            clearInterval(this.stopCheckInterval);
        }
        return new Promise((resolve) => {
            this.stopCheckInterval = setInterval(async () => {
                if (this.redisClient.isOpen && this.subscriptionClient?.isOpen) {
                    if (this.stopCheckInterval) {
                        clearInterval(this.stopCheckInterval);
                    }
                    await this._stop();
                    resolve();
                }
            }, 100);
        });
    }
    async reelect() {
        if (this.__state === "leader") {
            this.votedFor = "";
            this.startTimeout();
        }
    }
    stepdown() {
        return this.reelect();
    }
    async messageFollowers(message) {
        await this.redisClient.publish(`consensus-messages:${this.kind}:followers`, JSON.stringify({
            message,
            from: this.__instanceId,
            fromLeader: this.__state === "leader",
        }));
    }
    async messageTo(to, message) {
        await this.redisClient.publish(`consensus-messages:${this.kind}:${to}`, JSON.stringify({
            message,
            from: this.__instanceId,
            fromLeader: this.__state === "leader",
        }));
    }
    async messageAll(message) {
        await this.redisClient.publish(`consensus-messages:${this.kind}`, JSON.stringify({
            message,
            from: this.__instanceId,
            fromLeader: this.__state === "leader",
        }));
    }
    async messageLeader(message) {
        await this.redisClient.publish(`consensus-messages:${this.kind}:leader`, JSON.stringify({ message, from: this.__instanceId }));
    }
    get currentTerm() {
        return this.__currentTerm;
    }
    get id() {
        return this.__instanceId;
    }
    get state() {
        return this.__state;
    }
    async getLeader() {
        const instances = await this.getInstances();
        return instances.find((instance) => instance.state === "leader");
    }
    async setMeta(meta) {
        this.__meta = meta;
        await this.keepAlive();
    }
    get meta() {
        return this.__meta;
    }
}
export default Candidate;