Add Blink Prometheus listener (#11509)

bskylink/src/index.ts

@@ -4,10 +4,12 @@ import type http from 'node:http'
 import cors from 'cors'
 import express from 'express'
 import {createHttpTerminator, type HttpTerminator} from 'http-terminator'
+import {type Registry} from 'prom-client'
 
 import {type Config} from './config.js'
 import {AppContext} from './context.js'
 import i18n from './i18n.js'
+import {createPrometheusRegistry} from './prometheus.js'
 import {default as routes, errorHandler} from './routes/index.js'
 
 export * from './config.js'
@@ -16,12 +18,17 @@ export * from './logger.js'
 
 export class LinkService {
   public server?: http.Server
+  public metricsServer?: http.Server
   private terminator?: HttpTerminator
+  private metricsTerminator?: HttpTerminator
+  private metricsRegistry: Registry
 
   constructor(
     public app: express.Application,
     public ctx: AppContext,
-  ) {}
+  ) {
+    this.metricsRegistry = createPrometheusRegistry(ctx)
+  }
 
   static async create(cfg: Config): Promise<LinkService> {
     let app = express()
@@ -41,11 +48,26 @@ export class LinkService {
     this.server.keepAliveTimeout = 90000
     this.terminator = createHttpTerminator({server: this.server})
     await events.once(this.server, 'listening')
+
+    const metricsApp = express()
+    metricsApp.get('/metrics', (_req, res, next) => {
+      res.set('Content-Type', this.metricsRegistry.contentType)
+      this.metricsRegistry.metrics().then(metrics => res.end(metrics), next)
+    })
+    this.metricsServer = metricsApp.listen(this.ctx.cfg.service.metricsPort)
+    this.metricsTerminator = createHttpTerminator({
+      server: this.metricsServer,
+      gracefulTerminationTimeout: 2000,
+    })
+    await events.once(this.metricsServer, 'listening')
   }
 
   async destroy() {
     this.ctx.abortController.abort()
-    await this.terminator?.terminate()
+    await Promise.all([
+      this.terminator?.terminate(),
+      this.metricsTerminator?.terminate(),
+    ])
     await this.ctx.db.close()
     this.ctx.metrics.stop()
   }