feat: add support for `MONOLITH_TRANSPORTER` env var (#29373)

Co-authored-by: Debdut Chakraborty <debdut.chakraborty@rocket.chat>

.changeset/mean-guests-love.md

+---
+'@rocket.chat/meteor': minor
+---
+
+feat: *Enterprise* Add support for different transporters to connect multiple monolith instances.
+
+To use that, you can use the `TRANSPORTER` env var adding "monolith+" to the transporter value. To use NATS for example, your env var should be:
+
+```bash
+export TRANSPORTER="monolith+nats://localhost:4222"
+```

apps/meteor/ee/server/local-services/instance/getTransporter.ts

+export function getTransporter({ transporter, port }: { transporter?: string; port?: string } = {}) {
+	if (transporter) {
+		if (!transporter.match(/^(?:monolith\+)/)) {
+			throw new Error('invalid transporter');
+		}
+
+		const [, ...url] = transporter.split('+');
+		return url.join('');
+	}
+
+	return {
+		port: port ? port.trim() : 0,
+		udpDiscovery: false,
+	};
+}

apps/meteor/ee/server/local-services/instance/service.ts

 import os from 'os';
 
 import type { BrokerNode } from 'moleculer';
-import { ServiceBroker } from 'moleculer';
+import { ServiceBroker, Transporters } from 'moleculer';
 import { License, ServiceClassInternal } from '@rocket.chat/core-services';
 import { InstanceStatus as InstanceStatusRaw } from '@rocket.chat/models';
 import { InstanceStatus } from '@rocket.chat/instance-status';
 
 import { StreamerCentral } from '../../../../server/modules/streamer/streamer.module';
 import type { IInstanceService } from '../../sdk/types/IInstanceService';
+import { getTransporter } from './getTransporter';
 
 export class InstanceService extends ServiceClassInternal implements IInstanceService {
 	protected name = 'instance';
 
 	private broadcastStarted = false;
 
+	private transporter: Transporters.TCP | Transporters.NATS;
+
+	private isTransporterTCP = true;
+
 	private broker: ServiceBroker;
 
 	private troubleshootDisableInstanceBroadcast = false;
@@ -21,15 +26,25 @@ export class InstanceService extends ServiceClassInternal implements IInstanceSe
 	constructor() {
 		super();
 
-		this.onEvent('watch.instanceStatus', async ({ clientAction, data }): Promise<void> => {
-			if (clientAction === 'removed') {
-				return;
-			}
+		const tx = getTransporter({ transporter: process.env.TRANSPORTER, port: process.env.TCP_PORT });
+		if (typeof tx === 'string') {
+			this.transporter = new Transporters.NATS({ url: tx });
+			this.isTransporterTCP = false;
+		} else {
+			this.transporter = new Transporters.TCP(tx);
+		}
 
-			if (clientAction === 'inserted' && data?.extraInformation?.port) {
-				this.connectNode(data);
-			}
-		});
+		if (this.isTransporterTCP) {
+			this.onEvent('watch.instanceStatus', async ({ clientAction, data }): Promise<void> => {
+				if (clientAction === 'removed') {
+					return;
+				}
+
+				if (clientAction === 'inserted' && data?.extraInformation?.tcpPort) {
+					this.connectNode(data);
+				}
+			});
+		}
 
 		this.onEvent('license.module', async ({ module, valid }) => {
 			if (module === 'scalability' && valid) {
@@ -60,17 +75,9 @@ export class InstanceService extends ServiceClassInternal implements IInstanceSe
 	}
 
 	async created() {
-		const port = process.env.TCP_PORT ? String(process.env.TCP_PORT).trim() : 0;
-
 		this.broker = new ServiceBroker({
 			nodeID: InstanceStatus.id(),
-			transporter: {
-				type: 'TCP',
-				options: {
-					port,
-					udpDiscovery: false,
-				},
-			},
+			transporter: this.transporter,
 		});
 
 		this.broker.createService({
@@ -135,18 +142,20 @@ export class InstanceService extends ServiceClassInternal implements IInstanceSe
 
 		StreamerCentral.on('broadcast', this.sendBroadcast.bind(this));
 
-		await InstanceStatusRaw.find(
-			{
-				'extraInformation.tcpPort': {
-					$exists: true,
+		if (this.isTransporterTCP) {
+			await InstanceStatusRaw.find(
+				{
+					'extraInformation.tcpPort': {
+						$exists: true,
+					},
 				},
-			},
-			{
-				sort: {
-					_createdAt: -1,
+				{
+					sort: {
+						_createdAt: -1,
+					},
 				},
-			},
-		).forEach(this.connectNode.bind(this));
+			).forEach(this.connectNode.bind(this));
+		}
 	}
 
 	private connectNode(record: any) {

apps/meteor/ee/tests/unit/apps/meteor/ee/server/local-services/instance/getTransporter.spec.ts

+import { expect } from 'chai';
+
+import { getTransporter } from '../../../../../../../../server/local-services/instance/getTransporter';
+
+describe('getTransporter', () => {
+	it('should return TCP with port 0 by default', () => {
+		expect(getTransporter()).to.deep.equal({ port: 0, udpDiscovery: false });
+	});
+
+	it('should return TCP with port set via env var', () => {
+		expect(getTransporter({ port: '1234' })).to.deep.equal({ port: '1234', udpDiscovery: false });
+
+		expect(getTransporter({ port: '   1234' })).to.deep.equal({ port: '1234', udpDiscovery: false });
+
+		expect(getTransporter({ port: '   1234   ' })).to.deep.equal({ port: '1234', udpDiscovery: false });
+	});
+
+	it('should throw if transporter set incorrectly', () => {
+		expect(() => getTransporter({ transporter: 'something' })).to.throw('invalid transporter');
+	});
+
+	it('should return transporter if set correctly', () => {
+		expect(getTransporter({ transporter: 'monolith+nats://address' })).to.equal('nats://address');
+	});
+});