feat: api ingestion metrics on prometheus (#113)

src/index.ts

@@ -3,6 +3,7 @@ import { isProdEnv } from './api/util/helpers';
 import { buildChainhookServer } from './chainhook/server';
 import { ENV } from './env';
 import { logger } from './logger';
+import { ApiMetrics } from './metrics/metrics';
 import { PgStore } from './pg/pg-store';
 import { registerShutdownConfig } from './shutdown-handler';
 
@@ -43,6 +44,7 @@ async function initApiService(db: PgStore) {
       },
     });
 
+    ApiMetrics.configure(db);
     await promServer.listen({ host: ENV.API_HOST, port: 9153 });
   }
 }

src/metrics/metrics.ts

@@ -0,0 +1,42 @@
+import * as prom from 'prom-client';
+import { PgStore } from '../pg/pg-store';
+
+export class ApiMetrics {
+  /** The most recent Bitcoin block height ingested by the API */
+  readonly ordinals_api_block_height: prom.Gauge;
+  /** Maximum blessed inscription number */
+  readonly ordinals_api_max_inscription_number: prom.Gauge;
+  /** Maximum cursed inscription number */
+  readonly ordinals_api_max_cursed_inscription_number: prom.Gauge;
+
+  static configure(db: PgStore): ApiMetrics {
+    return new ApiMetrics(db);
+  }
+
+  private constructor(db: PgStore) {
+    this.ordinals_api_block_height = new prom.Gauge({
+      name: `ordinals_api_block_height`,
+      help: 'The most recent Bitcoin block height ingested by the API',
+      async collect() {
+        const height = await db.getChainTipBlockHeight();
+        this.set(height);
+      },
+    });
+    this.ordinals_api_max_inscription_number = new prom.Gauge({
+      name: `ordinals_api_max_inscription_number`,
+      help: 'Maximum blessed inscription number',
+      async collect() {
+        const max = await db.getMaxInscriptionNumber();
+        if (max) this.set(max);
+      },
+    });
+    this.ordinals_api_max_cursed_inscription_number = new prom.Gauge({
+      name: `ordinals_api_max_cursed_inscription_number`,
+      help: 'Maximum cursed inscription number',
+      async collect() {
+        const max = await db.getMaxCursedInscriptionNumber();
+        if (max) this.set(max);
+      },
+    });
+  }
+}