feat: expose prometheus metrics endpoint

package.json

@@ -39,6 +39,7 @@
     "forever": "^4.0.3",
     "lodash": "^4.17.21",
     "pino": "^8.7.0",
+    "prom-client": "^14.1.0",
     "reflect-metadata": "^0.1.13",
     "tslib": "^2.4.0",
     "tslog": "^3.3.4",

src/services/healthChecker.ts

@@ -1,6 +1,7 @@
 import formatDuration from "date-fns/formatDuration";
 import intervalToDuration from "date-fns/intervalToDuration";
 import express from "express";
+import { Gauge, register } from "prom-client";
 import { Inject, Service } from "typedi";
 
 import config from "../config";
@@ -22,12 +23,36 @@ export class HealthChecker {
     const start = new Date();
     const app = express();
 
+    const latestBlockGauge = new Gauge({
+      name: "latest_block",
+      help: "Latest processed block",
+    });
+    const startTimeGauge = new Gauge({
+      name: "start_time",
+      help: "Start time, in unixtime",
+    });
+    startTimeGauge.set(start.valueOf());
+    const healthyGauge = new Gauge({
+      name: "healthy",
+      help: "Is service healthy",
+    });
+    healthyGauge.set(1);
+
     app.get("/", (_, res) => {
       res.send({
         latestBlock: this.scanService.lastUpdated,
         uptime: formatDuration(intervalToDuration({ start, end: new Date() })),
       });
     });
+    app.get("/metrics", async (_, res) => {
+      try {
+        latestBlockGauge.set(this.scanService.lastUpdated);
+        res.set("Content-Type", register.contentType);
+        res.end(await register.metrics());
+      } catch (ex) {
+        res.status(500).end(ex);
+      }
+    });
 
     app.listen(config.port, () => {
       this.log.info(`started on port ${config.port}`);

yarn.lock

@@ -2748,6 +2748,11 @@ bindings@^1.5.0:
   dependencies:
     file-uri-to-path "1.0.0"
 
+[email protected]:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/bintrees/-/bintrees-1.0.2.tgz#49f896d6e858a4a499df85c38fb399b9aff840f8"
+  integrity sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw==
+
 bn.js@^4.11.9:
   version "4.12.0"
   resolved "https://registry.yarnpkg.com/bn.js/-/bn.js-4.12.0.tgz#775b3f278efbb9718eec7361f483fb36fbbfea88"
@@ -6050,6 +6055,13 @@ process@^0.11.10:
   resolved "https://registry.yarnpkg.com/process/-/process-0.11.10.tgz#7332300e840161bda3e69a1d1d91a7d4bc16f182"
   integrity sha512-cdGef/drWFoydD1JsMzuFf8100nZl+GT+yacc2bEced5f9Rjk4z+WtFUTBu9PhOi9j/jfmBPu0mMEY4wIdAF8A==
 
+prom-client@^14.1.0:
+  version "14.1.0"
+  resolved "https://registry.yarnpkg.com/prom-client/-/prom-client-14.1.0.tgz#049609859483d900844924df740722c76ed1fdbb"
+  integrity sha512-iFWCchQmi4170omLpFXbzz62SQTmPhtBL35v0qGEVRHKcqIeiexaoYeP0vfZTujxEq3tA87iqOdRbC9svS1B9A==
+  dependencies:
+    tdigest "^0.1.1"
+
 [email protected]:
   version "0.2.14"
   resolved "https://registry.yarnpkg.com/prompt/-/prompt-0.2.14.tgz#57754f64f543fd7b0845707c818ece618f05ffdc"
@@ -6921,6 +6933,13 @@ tapable@^2.2.0:
   resolved "https://registry.yarnpkg.com/tapable/-/tapable-2.2.1.tgz#1967a73ef4060a82f12ab96af86d52fdb76eeca0"
   integrity sha512-GNzQvQTOIP6RyTfE2Qxb8ZVlNmw0n88vp1szwWRimP02mnTsx3Wtn5qRdqY9w2XduFNUgvOwhNnQsjwCp+kqaQ==
 
+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"
+
 text-extensions@^1.0.0:
   version "1.9.0"
   resolved "https://registry.yarnpkg.com/text-extensions/-/text-extensions-1.9.0.tgz#1853e45fee39c945ce6f6c36b2d659b5aabc2a26"