fix(metrics): use path pattern instead of raw path in path labels

Signed-off-by: nflaig <nflaig@protonmail.com>

extensions/metrics/src/__tests__/acceptance/metrics.acceptance.ts

@@ -254,6 +254,19 @@ describe('Metrics (acceptance)', () => {
         /loopback_invocation_duration_summary{quantile="0.01",targetName="MockController.prototype.success",method="GET",path="\/success",statusCode="204"}/,
       );
     });
+
+    it('uses the path pattern instead of the raw path in path labels', async () => {
+      await request.get('/path/1');
+      await request.get('/path/1/2');
+
+      const res = await request
+        .get('/metrics')
+        .expect(200)
+        .expect('content-type', /text/);
+
+      expect(res.text).to.match(/path="\/path\/{param}"/);
+      expect(res.text).to.match(/path="\/path\/{firstParam}\/{secondParam}"/);
+    });
   });
 
   context('with configured default labels', () => {

extensions/metrics/src/__tests__/acceptance/mock.controller.ts

@@ -8,6 +8,7 @@ import {
   del,
   get,
   HttpErrors,
+  param,
   patch,
   post,
   put,
@@ -63,4 +64,13 @@ export class MockController {
   serverError() {
     throw new Error();
   }
+
+  @get('/path/{param}')
+  pathWithParam(@param.path.string('param') _param: string) {}
+
+  @get('/path/{firstParam}/{secondParam}')
+  pathWithParams(
+    @param.path.string('firstParam') _firstParam: string,
+    @param.path.string('secondParam') _secondParam: string,
+  ) {}
 }

extensions/metrics/src/interceptors/metrics.interceptor.ts

@@ -9,10 +9,17 @@ import {
   injectable,
   Interceptor,
   InvocationContext,
+  InvocationSource,
   Provider,
   ValueOrPromise,
 } from '@loopback/core';
-import {HttpErrors, RequestContext, Response} from '@loopback/rest';
+import {
+  HttpErrors,
+  Request,
+  RequestContext,
+  Response,
+  RouteSource,
+} from '@loopback/rest';
 import {
   Counter,
   Gauge,
@@ -90,8 +97,8 @@ export class MetricsInterceptor implements Provider<Interceptor> {
     const labelValues: LabelValues<LabelNames> = {
       targetName: invocationCtx.targetName,
       method: request.method,
-      path: request.path,
     };
+    labelValues.path = getPathPattern(invocationCtx, request);
     const endGauge = MetricsInterceptor.gauge.startTimer();
     const endHistogram = MetricsInterceptor.histogram.startTimer();
     const endSummary = MetricsInterceptor.summary.startTimer();
@@ -111,6 +118,13 @@ export class MetricsInterceptor implements Provider<Interceptor> {
   }
 }
 
+function getPathPattern({source}: InvocationContext, request: Request) {
+  // make sure to use path pattern instead of raw path
+  // this is important since paths can contain unbounded sets of values
+  // such as IDs which would create a new time series for each unique value
+  return isRouteSource(source) ? source.value.path : request.path;
+}
+
 function getStatusCodeFromResponse(response: Response, result?: unknown) {
   // interceptors are invoked before result is written to response,
   // the status code for 200 responses without a result should be 204
@@ -124,3 +138,7 @@ function getStatusCodeFromError(err: HttpErrors.HttpError) {
   const notFound = err.code === 'ENTITY_NOT_FOUND';
   return err.statusCode ?? err.status ?? (notFound ? 404 : 500);
 }
+
+function isRouteSource(source?: InvocationSource): source is RouteSource {
+  return source?.type === 'route';
+}