Move Prometheus metrics server into a separated file (#3391)gh-2124

This will make the code a bit more readable and the Prometheus server more easy to maintain.

2 files changed, 24 insertions, 13 deletions

diff --git a/app.js b/app.js
index b72831fdb..a8554c534 100755
--- a/app.js
+++ b/app.js
@@ -57,6 +57,7 @@ import { RouteAPI } from './lib/handlers/route-api';
 import { SourceHandler } from './lib/handlers/source';
 import { languages as allLanguages } from './lib/languages';
 import { logger, logToLoki, logToPapertrail, suppressConsoleLog } from './lib/logger';
+import { setupMetricsServer } from './lib/metrics-server';
 import { ClientOptionsHandler } from './lib/options-handler';
 import * as props from './lib/properties';
 import { ShortLinkResolver } from './lib/shortener/google';
@@ -547,19 +548,7 @@ async function main() {
 
     if (opts.metricsPort) {
         logger.info(`Running metrics server on port ${opts.metricsPort}`);
-        PromClient.collectDefaultMetrics();
-        const metricsServer = express();
-
-        metricsServer.get('/metrics', async (req, res) => {
-            try {
-                res.set('Content-Type', PromClient.register.contentType);
-                res.end(await PromClient.register.metrics());
-            } catch (ex) {
-                res.status(500).end(ex);
-            }
-        });
-
-        metricsServer.listen(opts.metricsPort, defArgs.hostname);
+        setupMetricsServer(opts.metricsPort, defArgs.hostname);
     }
 
     webServer
diff --git a/lib/metrics-server.ts b/lib/metrics-server.ts
new file mode 100644
index 000000000..eb8debc5d
--- /dev/null
+++ b/lib/metrics-server.ts
@@ -0,0 +1,22 @@
+import express from 'express';
+import PromClient from 'prom-client';
+
+/**
+ * Will launch the Prometheus metrics server
+ *
+ * @param serverPort - The listening port to bind into this metrics server.
+ * @param hostname - The TCP host to attach the listener.
+ * @returns void
+ */
+export function setupMetricsServer(serverPort: number, hostname: string): void {
+    PromClient.collectDefaultMetrics();
+    const metricsServer = express();
+
+    metricsServer.get('/metrics', (req, res) => {
+      PromClient.register.metrics()
+        .then(metrics => { res.header('Content-Type', PromClient.register.contentType).send(metrics); })
+        .catch(err => res.status(500).send(err));
+    });
+
+    metricsServer.listen(serverPort, hostname);
+}