feat(api): Implement healthcheck HTTP API endpoint.

Fixes #838.

server/api/healthcheck/index.app-tests.ts

@@ -0,0 +1,19 @@
+// eslint-disable-next-line import/no-unassigned-import
+import 'regenerator-runtime/runtime.js';
+import {assert} from 'chai';
+import request from 'supertest';
+
+import {server} from '../../../imports/_test/fixtures';
+
+import absoluteURL from '../../../imports/app/absoluteURL';
+
+const app = absoluteURL('api/healthcheck');
+
+server(__filename, () => {
+	it('works', async () => {
+		const response = await request(app).get(`/`);
+
+		assert.equal(response.status, 200);
+		assert.equal(response.text, 'OK');
+	});
+});

server/api/healthcheck/index.ts

@@ -0,0 +1,25 @@
+import process from 'process';
+
+import express from 'express';
+
+import isProduction from '../../../imports/app/isProduction';
+import isReady from '../../../imports/app/isReady';
+
+import {pipe} from '../rateLimit';
+
+import rateLimiter from './rateLimiter';
+
+const routes = express();
+
+routes.set('trust proxy', process.env.HTTP_FORWARDED_COUNT);
+
+if (isProduction()) {
+	routes.use(pipe(rateLimiter));
+}
+
+routes.get(`/`, async (_req, res, _next) => {
+	await isReady();
+	res.status(200).send('OK');
+});
+
+export default routes;

server/api/healthcheck/rateLimiter.ts

@@ -0,0 +1,11 @@
+import {RateLimiterMemory} from 'rate-limiter-flexible';
+
+const rateLimiter = new RateLimiterMemory({
+	// NOTE key prefix is not necessary since each RateLimiterMemory is backed
+	// by its own storage.
+	keyPrefix: '',
+	points: 15, // NOTE 6 points
+	duration: 60, // NOTE Per minute
+});
+
+export default rateLimiter;

server/main.ts

@@ -17,9 +17,11 @@ import scheduleAllMigrations from '../imports/migrations/scheduleAll';
 import './publication/_register/enabled';
 
 import ics from './api/ics/index';
+import healthcheck from './api/healthcheck/index';
 
-// DECLARE ALL ENABLED ICS ENDPOINTS
+// DECLARE ALL ENABLED HTTP ENDPOINTS
 WebApp.connectHandlers.use('/api/ics', ics);
+WebApp.connectHandlers.use('/api/healthcheck', healthcheck);
 
 if (isTest()) {
 	// @ts-expect-error Missing from type definitions.