feat: Prometheus metrics for indexer

packages/graphql/src/application/uc/GetMetrics.ts

@@ -0,0 +1,33 @@
+import { client } from '~/graphql/GraphQLSDK';
+import BlockDAO from '~/infra/dao/BlockDAO';
+
+export default class GetMetrics {
+  async getFuelCoreLastBlockHeight() {
+    const { data } = await client.sdk.blocks({ last: 1 });
+    const blocks = data.blocks;
+    const [lastBlock] = blocks.nodes;
+    const height = Number(lastBlock?.header.height ?? '0');
+    return height;
+  }
+
+  async getIndexerLastBlockHeight() {
+    const blockDAO = new BlockDAO();
+    const latestBlock = await blockDAO.findLatestBlockAdded();
+    const blockId = latestBlock ? latestBlock.id : 0;
+    return blockId;
+  }
+
+  async execute(): Promise<any> {
+    const fuelCoreLastBlockHeight = await this.getFuelCoreLastBlockHeight();
+    const indexerLastBlockHeight = await this.getIndexerLastBlockHeight();
+    const indexerBlockHeightDelay =
+      fuelCoreLastBlockHeight - indexerLastBlockHeight;
+    const indexerHealth = indexerBlockHeightDelay < 100 ? 1 : 0;
+    return {
+      explorer_indexer_fuel_core_last_block_height: fuelCoreLastBlockHeight,
+      explorer_indexer_last_block_height_synced: indexerLastBlockHeight,
+      explorer_indexer_block_height_sync_delay: indexerBlockHeightDelay,
+      explorer_indexer_health: indexerHealth,
+    };
+  }
+}

packages/graphql/src/infra/server/App.ts

@@ -1,11 +1,23 @@
 import cors from 'cors';
-import express from 'express';
+import express, { Request, Response } from 'express';
+import GetMetrics from '~/application/uc/GetMetrics';
 
 export class Server {
   setup() {
     const app = express();
     app.use(cors<cors.CorsRequest>());
     app.use(express.json());
+
+    app.get('/metrics', async (_req: Request, res: Response) => {
+      const getMetrics = new GetMetrics();
+      const output = await getMetrics.execute();
+      const lines: any = [];
+      for (const element in output) {
+        lines.push(`${element} ${output[element]}`);
+      }
+      res.setHeader('content-type', 'text/plain');
+      res.send(lines.join('\n'));
+    });
     return app;
   }