Use path.Join for constructing Loki query URL

CHANGELOG.md

@@ -96,6 +96,7 @@ To learn more about active deprecations, we recommend checking [GitHub Discussio
 - **Github Runner Scaler**: Improve URL construction and error handling ([#7495](https://github.com/kedacore/keda/pull/7495))
 - **Github Runner Scaler**: Limit HTTP error response logging ([#7469](https://github.com/kedacore/keda/pull/7469))
 - **Loki Scaler**: Limit HTTP error response logging ([#7469](https://github.com/kedacore/keda/pull/7469))
+- **Loki Scaler**: `serverAddress` now appends `/loki/api/v1/query` to the end of existing path instead of overriding ([#7648](https://github.com/kedacore/keda/pull/7648))
 - **Metrics API Scaler**: Fix `aggregateFromKubeServiceEndpoints` using empty label selector that matched all EndpointSlices in the namespace instead of only the target service's ([#7641](https://github.com/kedacore/keda/issues/7641))
 - **NATS JetStream Scaler**: URL-encode user input in monitoring URL construction ([#7483](https://github.com/kedacore/keda/pull/7483))
 - **Prometheus Scaler**: Handle NaN results in the same manner as Inf ([#7475](https://github.com/kedacore/keda/issues/7475))

pkg/scalers/loki_scaler.go

@@ -7,7 +7,9 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"path"
 	"strconv"
+	"strings"
 
 	"github.com/go-logr/logr"
 	v2 "k8s.io/api/autoscaling/v2"
@@ -115,11 +117,10 @@ func (s *lokiScaler) GetMetricSpecForScaling(context.Context) []v2.MetricSpec {
 }
 
 func (s *lokiScaler) ExecuteLokiQuery(ctx context.Context) (float64, error) {
-	u, err := url.ParseRequestURI(s.metadata.ServerAddress)
+	u, err := getServerAddress(&s.metadata)
 	if err != nil {
 		return -1, err
 	}
-	u.Path = "/loki/api/v1/query"
 	u.RawQuery = url.Values{"query": []string{s.metadata.Query}}.Encode()
 
 	req, err := http.NewRequestWithContext(ctx, "GET", u.String(), nil)
@@ -218,3 +219,26 @@ func (s *lokiScaler) GetMetricsAndActivity(ctx context.Context, metricName strin
 	metric := GenerateMetricInMili(metricName, val)
 	return []external_metrics.ExternalMetricValue{metric}, val > s.metadata.ActivationThreshold, nil
 }
+
+func getServerAddress(metadata *lokiMetadata) (url.URL, error) {
+	const lokiPath = "/loki/api/v1/query"
+	u, err := url.ParseRequestURI(metadata.ServerAddress)
+	if err != nil {
+		return url.URL{}, err
+	}
+
+	u.Path = strings.TrimRight(u.Path, "/")
+
+	if u.Path == lokiPath {
+		return *u, nil
+	}
+
+	if strings.HasPrefix(lokiPath, u.Path+"/") {
+		remaining := strings.TrimPrefix(lokiPath, u.Path)
+		u.Path = path.Join(u.Path, remaining)
+	} else {
+		u.Path = path.Join(u.Path, lokiPath)
+	}
+
+	return *u, nil
+}

pkg/scalers/loki_scaler_test.go

@@ -250,3 +250,81 @@ func TestLokiScalerTenantHeader(t *testing.T) {
 	_, err := scaler.ExecuteLokiQuery(context.TODO())
 	assert.NoError(t, err)
 }
+
+type getServerAddressTestData struct {
+	name          string
+	serverAddress string
+	expectedPath  string
+	isError       bool
+}
+
+var testGetServerAddressData = []getServerAddressTestData{
+	{
+		name:          "no path in URL",
+		serverAddress: "http://localhost:3100",
+		expectedPath:  "/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with trailing slash",
+		serverAddress: "http://localhost:3100/",
+		expectedPath:  "/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with partial loki path",
+		serverAddress: "http://localhost:3100/loki",
+		expectedPath:  "/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with longer partial loki path",
+		serverAddress: "http://localhost:3100/loki/api/v1",
+		expectedPath:  "/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with full loki path already present",
+		serverAddress: "http://localhost:3100/loki/api/v1/query",
+		expectedPath:  "/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with full loki path and trailing slash",
+		serverAddress: "http://localhost:3100/loki/api/v1/query/",
+		expectedPath:  "/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with custom prefix",
+		serverAddress: "http://localhost:3100/custom",
+		expectedPath:  "/custom/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "URL with partial loki path not on segment boundary",
+		serverAddress: "http://localhost:3100/lo",
+		expectedPath:  "/lo/loki/api/v1/query",
+		isError:       false,
+	},
+	{
+		name:          "invalid URL",
+		serverAddress: "not-a-url",
+		isError:       true,
+	},
+}
+
+func TestGetServerAddress(t *testing.T) {
+	for _, testData := range testGetServerAddressData {
+		t.Run(testData.name, func(t *testing.T) {
+			meta := &lokiMetadata{ServerAddress: testData.serverAddress}
+			u, err := getServerAddress(meta)
+			if testData.isError {
+				assert.Error(t, err)
+				return
+			}
+			assert.NoError(t, err)
+			assert.Equal(t, testData.expectedPath, u.Path)
+		})
+	}
+}