Expose basic Prometheus metrics

backend/server.js

@@ -5,6 +5,7 @@ import path from "path";
 import express from "express";
 import ws from "express-ws";
 import _ from "lodash";
+import * as promClient from "prom-client";
 
 import * as api from "./api.js";
 import { aliases, langsPromise } from "./langs.js";
@@ -20,12 +21,19 @@ const analyticsTag = (process.env.ANALYTICS_TAG || "").replace(
   "$1"
 );
 
+promClient.collectDefaultMetrics();
+
 const langs = await langsPromise;
 const app = express();
 
 app.set("query parser", (qs) => new URLSearchParams(qs));
 app.set("view engine", "ejs");
 
+app.get("/metrics", async (_, res) => {
+  res.contentType("text/plain; version=0.0.4");
+  res.send(await promClient.register.metrics());
+});
+
 app.get("/", (_, res) => {
   if (Object.keys(langs).length > 0) {
     res.render(path.resolve("frontend/pages/index"), {

package.json

@@ -31,6 +31,7 @@
     "p-queue": "^6.6.2",
     "parse-passwd": "^1.0.0",
     "prettier": "^2.3.1",
+    "prom-client": "^14.0.1",
     "regenerator-runtime": "^0.13.7",
     "semaphore": "^1.1.0",
     "strip-ansi": "^6.0.0",

yarn.lock

@@ -1362,6 +1362,11 @@ bindings@^1.5.0:
   dependencies:
     file-uri-to-path "1.0.0"
 
+bintrees@1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/bintrees/-/bintrees-1.0.1.tgz#0e655c9b9c2435eaab68bf4027226d2b55a34524"
+  integrity sha1-DmVcm5wkNeqraL9AJyJtK1WjRSQ=
+
 bluebird@^3.5.5:
   version "3.7.2"
   resolved "https://registry.yarnpkg.com/bluebird/-/bluebird-3.7.2.tgz#9f229c15be272454ffa973ace0dbee79a1b0c36f"
@@ -3595,6 +3600,13 @@ process@^0.11.10:
   resolved "https://registry.yarnpkg.com/process/-/process-0.11.10.tgz#7332300e840161bda3e69a1d1d91a7d4bc16f182"
   integrity sha1-czIwDoQBYb2j5podHZGn1LwW8YI=
 
+prom-client@^14.0.1:
+  version "14.0.1"
+  resolved "https://registry.yarnpkg.com/prom-client/-/prom-client-14.0.1.tgz#bdd9583e02ec95429677c0e013712d42ef1f86a8"
+  integrity sha512-HxTArb6fkOntQHoRGvv4qd/BkorjliiuO2uSWC2KC17MUTKYttWdDoXX/vxOhQdkoECEM9BBH0pj2l8G8kev6w==
+  dependencies:
+    tdigest "^0.1.1"
+
 promise-inflight@^1.0.1:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/promise-inflight/-/promise-inflight-1.0.1.tgz#98472870bf228132fcbdd868129bad12c3c029e3"
@@ -4221,6 +4233,13 @@ tapable@^1.0.0, tapable@^1.1.3:
   resolved "https://registry.yarnpkg.com/tapable/-/tapable-1.1.3.tgz#a1fccc06b58db61fd7a45da2da44f5f3a3e67ba2"
   integrity sha512-4WK/bYZmj8xLr+HUCODHGF1ZFzsYffasLUgEiMBY4fgtltdO6B4WJtlSbPaDTLpYTcGVwM2qLnFTICEcNxs3kA==
 
+tdigest@^0.1.1:
+  version "0.1.1"
+  resolved "https://registry.yarnpkg.com/tdigest/-/tdigest-0.1.1.tgz#2e3cb2c39ea449e55d1e6cd91117accca4588021"
+  integrity sha1-Ljyyw56kSeVdHmzZEReszKRYgCE=
+  dependencies:
+    bintrees "1.0.1"
+
 terser-webpack-plugin@^1.4.3:
   version "1.4.5"
   resolved "https://registry.yarnpkg.com/terser-webpack-plugin/-/terser-webpack-plugin-1.4.5.tgz#a217aefaea330e734ffacb6120ec1fa312d6040b"