Add option to serve Prometheus metrics #671 (#693)

Co-authored-by: Florent FAYOLLE <florent.fayolle@beta.gouv.fr>

README.md

@@ -304,6 +304,7 @@ PORT                | port number to listen on for Grist server
 REDIS_URL           | optional redis server for browser sessions and db query caching
 GRIST_SNAPSHOT_TIME_CAP       | optional. Define the caps for tracking buckets. Usage: {"hour": 25, "day": 32, "isoWeek": 12, "month": 96, "year": 1000}
 GRIST_SNAPSHOT_KEEP           | optional. Number of recent snapshots to retain unconditionally for a document, regardless of when they were made
+GRIST_PROMCLIENT_PORT         | optional. If set, serve the Prometheus metrics on the specified port number. ⚠️ Be sure to use a port which is not publicly exposed ⚠️.
 
 #### AI Formula Assistant related variables (all optional):
 

package.json

@@ -173,6 +173,7 @@
     "plotly.js-basic-dist": "2.13.2",
     "popper-max-size-modifier": "0.2.0",
     "popweasel": "0.1.20",
+    "prom-client": "14.2.0",
     "qrcode": "1.5.0",
     "randomcolor": "0.5.3",
     "redis": "3.1.1",

stubs/app/server/prometheus-exporter.ts

@@ -0,0 +1,25 @@
+import { collectDefaultMetrics, register } from 'prom-client';
+import http from 'http';
+
+const reqListener = (req: http.IncomingMessage, res: http.ServerResponse) => {
+  register.metrics().then((metrics) => {
+    res.writeHead(200, { 'Content-Type': register.contentType });
+    res.end(metrics);
+  }).catch((e) => {
+    res.writeHead(500);
+    res.end(e.message);
+  });
+};
+
+export function runPrometheusExporter(port: number) {
+  collectDefaultMetrics();
+
+  if (isNaN(port)) {
+    throw new Error(`Invalid port: ${process.env.GRIST_PROMCLIENT_PORT}`);
+  }
+  const server = http.createServer(reqListener);
+  server.listen(port, '0.0.0.0');
+
+  console.log(`Prometheus exporter listening on port ${port}.`);
+  return server;
+}

stubs/app/server/server.ts

@@ -36,6 +36,7 @@ setDefaultEnv('GRIST_WIDGET_LIST_URL', commonUrls.gristLabsWidgetRepository);
 import {updateDb} from 'app/server/lib/dbUtils';
 import {main as mergedServerMain, parseServerTypes} from 'app/server/mergedServerMain';
 import * as fse from 'fs-extra';
+import {runPrometheusExporter} from './prometheus-exporter';
 
 const G = {
   port: parseInt(process.env.PORT!, 10) || 8484,
@@ -102,6 +103,10 @@ export async function main() {
     console.log('For full logs, re-run with DEBUG=1');
   }
 
+  if (process.env.GRIST_PROMCLIENT_PORT) {
+    runPrometheusExporter(parseInt(process.env.GRIST_PROMCLIENT_PORT, 10));
+  }
+
   // If SAML is not configured, there's no login system, so provide a default email address.
   setDefaultEnv('GRIST_DEFAULT_EMAIL', 'you@example.com');
   // Set directory for uploaded documents.

yarn.lock

@@ -1739,6 +1739,11 @@ binary@~0.3.0:
     buffers "~0.1.1"
     chainsaw "~0.1.0"
 
+bintrees@1.0.2:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/bintrees/-/bintrees-1.0.2.tgz#49f896d6e858a4a499df85c38fb399b9aff840f8"
+  integrity sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw==
+
 bl@^4.0.3:
   version "4.1.0"
   resolved "https://registry.npmjs.org/bl/-/bl-4.1.0.tgz"
@@ -6520,6 +6525,13 @@ process@~0.11.0:
   resolved "https://registry.npmjs.org/process/-/process-0.11.10.tgz"
   integrity sha1-czIwDoQBYb2j5podHZGn1LwW8YI=
 
+prom-client@14.2.0:
+  version "14.2.0"
+  resolved "https://registry.yarnpkg.com/prom-client/-/prom-client-14.2.0.tgz#ca94504e64156f6506574c25fb1c34df7812cf11"
+  integrity sha512-sF308EhTenb/pDRPakm+WgiN+VdM/T1RaHj1x+MvAuT8UiQP8JmOEbxVqtkbfR4LrvOg5n7ic01kRBDGXjYikA==
+  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"
@@ -7688,6 +7700,13 @@ tar@^6.0.2, tar@^6.1.11, tar@^6.1.2:
     mkdirp "^1.0.3"
     yallist "^4.0.0"
 
+tdigest@^0.1.1:
+  version "0.1.2"
+  resolved "https://registry.yarnpkg.com/tdigest/-/tdigest-0.1.2.tgz#96c64bac4ff10746b910b0e23b515794e12faced"
+  integrity sha512-+G0LLgjjo9BZX2MfdvPfH+MKLCrxlXSYec5DaPYP1fe6Iyhf0/fSmJ0bFiZ1F8BT6cGXl2LpltQptzjXKWEkKA==
+  dependencies:
+    bintrees "1.0.2"
+
 term-size@^2.1.0:
   version "2.2.0"
   resolved "https://registry.npmjs.org/term-size/-/term-size-2.2.0.tgz"