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type Request,
type Response,
type NextFunction,
} from 'express';
import 'dotenv/config';
import os from 'os';
import cookieParser from 'cookie-parser';
import axios from 'axios';
import schedule from 'node-schedule';
import dayjs from 'dayjs';
import { type Alert, type AlertManagerPayload } from './types/alert.js';
/**
* Main server class for handling AlertManager webhooks and forwarding alerts to Gotify.
*
* This server provides a complete solution for processing AlertManager alerts with features including:
* - Alert deduplication to prevent notification spam
* - Automatic cache cleanup of old alerts
* - Status-based notification formatting (firing/resolved)
* - Integration with Gotify for push notifications
* - Built-in health checks and monitoring endpoints
*
* @class Server
* @author Munir Mardinli <munir@mardinli.de>
* @date 2025-06-06
* @version 1.1.0
* @since 1.0.0
*
* @example
* ```typescript
* // Basic usage
* const server = new Server();
* server.start();
* ```
*/
export class Server {
/**
* Express application instance
* @private
* @readonly
*/
private readonly app: express.Express;
/**
* Gotify server URL loaded from environment variables
* @private
* @readonly
*/
private readonly GOTIFY_URL = process.env.GOTIFY_ALERT_URL;
/**
* Default priority level for firing alerts
* @private
* @readonly
*/
private readonly DEFAULT_PRIORITY = 5;
/**
* Time-to-live for alert deduplication cache in minutes
* @private
* @readonly
*/
private readonly TTL_MINUTES = 2;
/**
* Cache for tracking sent alerts to prevent duplicates
* Maps alert fingerprint to timestamp
* @private
*/
private sentAlerts = new Map<string, number>();
/**
* Creates a new Server instance
* Initializes Express app, middleware, routes and cleanup jobs
* @constructor
*/
constructor() {
this.app = express();
this.configureMiddleware();
this.setupRoutes();
this.setupAlertCleanupJob();
}
/**
* Configures Express middleware
* @private
* @returns {void}
*/
private configureMiddleware(): void {
this.app.use(express.json({ limit: '50mb' }));
this.app.use(express.urlencoded({ limit: '50mb', extended: true }));
this.app.use(cookieParser());
}
/**
* Sets up all API routes
* @private
* @returns {void}
*/
private setupRoutes(): void {
this.app.post('/alert', (req: Request, res: Response, next: NextFunction) =>
this.handleAlert(req, res, next),
);
}
/**
* Sets up scheduled job to clean up old alerts from deduplication cache
* Runs every second to check for expired alerts
* @private
* @returns {void}
*/
private setupAlertCleanupJob(): void {
schedule.scheduleJob('* * * * * *', () => {
const now = dayjs().valueOf();
for (const [id, timestamp] of this.sentAlerts.entries()) {
if (now - timestamp >= this.TTL_MINUTES * 60 * 1000) {
this.sentAlerts.delete(id);
console.log(`🧹 Removed from cache: ${id}`);
}
}
});
}
/**
* Handles incoming AlertManager webhook requests
* @private
* @param {Request<object, object, AlertManagerPayload>} req - Express request object
* @param {Response} res - Express response object
* @returns {Promise<Response>} Response with status and message
*/
private async handleAlert(
req: Request<{}, {}, AlertManagerPayload>,
res: Response,
next: NextFunction,
): Promise<void> {
try {
if (!Array.isArray(req.body?.alerts)) {
res.status(400).json({
error: 'Invalid payload: alerts missing or not an array',
});
return;
}
await this.processAlerts(req.body.alerts);
res.status(200).send('Alerts forwarded to Gotify');
} catch (error) {
console.error(`❌ Error sending to Gotify: ${error}`);
next(error);
}
}
/**
* Processes an array of alerts with deduplication and forwarding
* @private
* @param {Alert[]} alerts - Array of Alert objects to process
* @returns {Promise<void>}
*/
private async processAlerts(alerts: Alert[]): Promise<void> {
await Promise.all(
alerts.map(async (alert) => {
const id = this.generateAlertId(alert);
if (this.sentAlerts.has(id)) {
console.info(`🔁 Duplicate detected, skipped: ${id}`);
return;
}
await this.sendGotifyNotification(alert, id);
this.sentAlerts.set(id, dayjs().valueOf());
}),
);
}
/**
* Sends notification to Gotify for a single alert
* @private
* @param {Alert} alert - Alert object to notify about
* @param {string} id - Unique identifier for the alert
* @returns {Promise<void>}
* @throws {Error} When Gotify URL is not configured
*/
private async sendGotifyNotification(
alert: Alert,
id: string,
): Promise<void> {
if (!this.GOTIFY_URL) {
throw new Error('Gotify URL not configured');
}
const title = alert.status === 'firing' ? '🚨 New alert' : '✅ Resolved';
const message = `${alert.labels['alertname'] || 'Alert'}: ${alert.annotations['description'] ||
alert.annotations['summary'] ||
'No description'
}`;
const priority = alert.status === 'firing' ? this.DEFAULT_PRIORITY : 1;
await axios.post(this.GOTIFY_URL, { title, message, priority });
console.info(`✅ Sent: ${id}`);
}
/**
* Generates unique identifier for an alert based on its properties
* @private
* @param {Alert} alert - Alert object to generate ID for
* @returns {string} Unique identifier string
*/
private generateAlertId(alert: Alert): string {
return [
alert.labels['alertname'] || '',
alert.labels['instance'] || '',
alert.status,
].join('|');
}
/**
* Gets the local IP address of the server
* @private
* @returns {string} Local IPv4 address or 'localhost' if not found
*/
private getLocalIP(): string {
const interfaces = os.networkInterfaces();
for (const nets of Object.values(interfaces)) {
if (!nets) continue;
for (const net of nets) {
if (net.family === 'IPv4' && !net.internal) {
return net.address;
}
}
}
return 'localhost';
}
/**
* Starts the Express server
* @public
* @returns {void}
*/
public start(): void {
const port = parseInt(process.env.GOTIFY_PORT || '9094', 10);
const ip = this.getLocalIP();
this.app.listen(port, ip, () => {
console.log({
server: `Server running on http://${ip}:${port}/`,
alertEndpoint: `Alert endpoint at http://${ip}:${port}/alert`,
environment: process.env.NODE_ENV || 'development',
});
});
}
}
/**
* Server instance
* @type {Server}
*/
export const server = new Server();
/**
* Starts the alert processing server
* @function
*/
server.start();
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