Write log entry when Azure DevOps API Rate Limit is (nearly) reached

Signed-off-by: Ruben Herrebrugh <raherrebrugh@gmail.com>

CHANGELOG.md

@@ -63,6 +63,7 @@ To learn more about active deprecations, we recommend checking [GitHub Discussio
 - **CloudEventSource**: Provide ClusterCloudEventSource around the management of TriggerAuthentication/ClusterTriggerAuthentication resources ([#3524](https://github.com/kedacore/keda/issues/3524))
 - **Github Action**: Fix panic when env for runnerScopeFromEnv or ownerFromEnv is empty ([#6156](https://github.com/kedacore/keda/issues/6156))
 - **RabbitMQ Scaler**: provide separate paremeters for user and password ([#2513](https://github.com/kedacore/keda/issues/2513))
+- **Azure Pipelines Scalar**: Print warning to log when Azure DevOps API Rate Limits are (nearly) reached ([#6284](https://github.com/kedacore/keda/issues/6284))
 
 #### Experimental
 

pkg/scalers/azure_pipelines_scaler.go

@@ -412,6 +412,16 @@ func getAzurePipelineRequest(ctx context.Context, logger logr.Logger, urlString
 		return []byte{}, fmt.Errorf("the Azure DevOps REST API returned error. urlString: %s status: %d response: %s", urlString, r.StatusCode, string(b))
 	}
 
+	// Log when API Rate Limits are reached
+	rateLimitRemaining := r.Header[http.CanonicalHeaderKey("X-RateLimit-Remaining")]
+	if rateLimitRemaining != nil {
+		logger.V(1).Info(fmt.Sprintf("Warning: ADO TSTUs Left %s. When reaching zero requests are delayed, lower the polling interval. See https://learn.microsoft.com/en-us/azure/devops/integrate/concepts/rate-limits?view=azure-devops", rateLimitRemaining))
+	}
+	rateLimitDelay := r.Header[http.CanonicalHeaderKey("X-RateLimit-Delay")]
+	if rateLimitDelay != nil {
+		logger.V(1).Info(fmt.Sprintf("Warning: Request to ADO API is delayed by %s seconds. Sending additional requests will increase delay until results are being blocked entirely", rateLimitDelay))
+	}
+
 	return b, nil
 }
 

pkg/scalers/azure_pipelines_scaler_test.go

@@ -222,6 +222,32 @@ func TestAzurePipelinesMatchedAgent(t *testing.T) {
 	}
 }
 
+func TestAzurePipelinesDelayed(t *testing.T) {
+	var apiStub = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Add("X-RateLimit-Limit", "0")
+		w.Header().Add("X-RateLimit-Delay", "42")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write(buildLoadJSON())
+	}))
+
+	meta := getMatchedAgentMetaData(apiStub.URL)
+
+	mockAzurePipelinesScaler := azurePipelinesScaler{
+		metadata:   meta,
+		httpClient: http.DefaultClient,
+	}
+
+	queueLen, err := mockAzurePipelinesScaler.GetAzurePipelinesQueueLength(context.TODO())
+
+	if err != nil {
+		t.Fail()
+	}
+
+	if queueLen < 1 {
+		t.Fail()
+	}
+}
+
 func getDemandJobMetaData(url string) *azurePipelinesMetadata {
 	meta := getMatchedAgentMetaData(url)
 	meta.parent = ""