⚡ - Otel servicegraph (#1506)

Co-authored-by: Diego Luisi <[email protected]>

app/packages/backend/package.json

@@ -48,7 +48,9 @@
     "express-promise-router": "^4.1.0",
     "node-gyp": "^9.0.0",
     "pg": "^8.11.3",
-    "winston": "^3.2.1"
+    "winston": "^3.2.1",
+    "express-prom-bundle": "^7.0.0",
+    "prom-client": "^15.0.0"
   },
   "devDependencies": {
     "@backstage/cli": "^0.25.0",
@@ -60,4 +62,4 @@
   "files": [
     "dist"
   ]
-}
+}

app/packages/backend/src/index.ts

@@ -35,6 +35,7 @@ import { ServerPermissionClient } from '@backstage/plugin-permission-node';
 import { DefaultIdentityClient } from '@backstage/plugin-auth-node';
 import kubernetes from './plugins/kubernetes';
 import todo from './plugins/todo';
+import { metricsHandler } from './metrics';
 
 function makeCreateEnv(config: Config) {
   const root = getRootLogger();
@@ -110,7 +111,8 @@ async function main() {
 
   const service = createServiceBuilder(module)
     .loadConfig(config)
-.addRouter('', await healthcheck(healthcheckEnv))
+    .addRouter('', await healthcheck(healthcheckEnv))
+    .addRouter('', metricsHandler())
     .addRouter('/api', apiRouter)
     .addRouter('', await app(appEnv));
 

app/packages/backend/src/metrics.ts

@@ -0,0 +1,40 @@
+// packages/backend/src/metrics.ts
+import { useHotCleanup } from '@backstage/backend-common';
+import { RequestHandler } from 'express';
+import promBundle from 'express-prom-bundle';
+import prom from 'prom-client';
+import * as url from 'url';
+
+const rootRegEx = new RegExp('^/([^/]*)/.*');
+const apiRegEx = new RegExp('^/api/([^/]*)/.*');
+
+export function normalizePath(req: any): string {
+  const path = url.parse(req.originalUrl || req.url).pathname || '/';
+
+  // Capture /api/ and the plugin name
+  if (apiRegEx.test(path)) {
+    return path.replace(apiRegEx, '/api/$1');
+  }
+
+  // Only the first path segment at root level
+  return path.replace(rootRegEx, '/$1');
+}
+
+/**
+ * Adds a /metrics endpoint, register default runtime metrics and instrument the router.
+ */
+export function metricsHandler(): RequestHandler {
+  // We can only initialize the metrics once and have to clean them up between hot reloads
+  useHotCleanup(module, () => prom.register.clear());
+
+  return promBundle({
+    includeMethod: true,
+    includePath: true,
+    // Using includePath alone is problematic, as it will include path labels with high
+    // cardinality (e.g. path params). Instead we would have to template them. However, this
+    // is difficult, as every backend plugin might use different routes. Instead we only take
+    // the first directory of the path, to have at least an idea how each plugin performs:
+    normalizePath,
+    promClient: { collectDefaultMetrics: {} },
+  });
+}