aurora failover

index.js

const mysql = require('mysql');


class MysqlAdapter {
    constructor() {
        this.connectionType = 'MASTER';
        this.waitingForAutoFaileOverSwitch = false;
        this.poolCluster = mysql.createPoolCluster();
        this.poolCluster.add(this.connectionType, {
            host: 'localhost',
            user: 'app',
            password: 'root',
            database: 'app'
        });

        this.intervalID = setInterval(() => {
            if (this.waitingForAutoFaileOverSwitch) return;
            this.excute('SHOW VARIABLES LIKE \'read_only\';').then(res => {
                // if read only is on then its mean a fail over is accoure and swe need to switch all connection in poll to secondry database
                if (res[0].Value === 'ON') {
                    this.waitingForAutoFaileOverSwitch = true
                    this.poolCluster.end(() => {
                        this.waitingForAutoFaileOverSwitch = false
                    });
                };
            });
        }, 5000);

    }
    async excute(query) {
        // delay all incoming request until pool kill all connection to read only database
        if (this.waitingForAutoFaileOverSwitch) {
            return new Promise((resolve, reject) => {
                setTimeout(() => {
                    this.excute(query).then(res => {
                        resolve(res);
                    });
                }, 1000);
            });
        }
        return new Promise((resolve, reject) => {

            this.poolCluster.getConnection(this.connectionType, (err, connection) => {
                if (err) {
                    reject(err);
                }
                connection.query(query, (err, rows) => {
                    connection.release();
                    if (err) {
                        reject(err);
                    }
                    resolve(rows);
                });
            });
        });
    }
}



const adapter = new MysqlAdapter();