fix breaking change in prom metrics validation scheme (#2781) (#2783)

* fix breaking change in prom metrics validation scheme

* add test and changelog

* punctuation

CHANGELOG.md

@@ -7,6 +7,15 @@ This document contains a historical list of changes between releases. Only
 changes that impact end-user behavior are listed; changes to documentation or
 internal API changes are not present.
 
+v1.7.0-rc.2
+-----------------
+
+### Bugfixes
+
+- Fix an issue where Prometheus metric name validation scheme was set by default to UTF-8. It is now set back to the
+  previous "legacy" scheme. An experimental flag `--feature.prometheus.metric-validation-scheme` can be used to switch 
+  it to `utf-8` to experiment with UTF-8 support.
+
 v1.7.0-rc.1
 -----------------
 

docs/sources/reference/cli/run.md

@@ -60,6 +60,7 @@ The following flags are supported:
 * `--config.extra-args`: Extra arguments from the original format used by the converter.
 * `--stability.level`: The minimum permitted stability level of functionality to run. Supported values: `experimental`, `public-preview`, `generally-available` (default `"generally-available"`).
 * `--feature.community-components.enabled`: Enable community components (default `false`).
+* `--feature.prometheus.metric-validation-scheme`: Prometheus metric validation scheme to use. Supported values: `legacy`, `utf-8`. NOTE: this is an experimental flag and may be removed in future releases (default `"legacy"`).
 
 ## Update the configuration file
 

internal/alloycli/cmd_run.go

@@ -20,6 +20,7 @@ import (
 	"github.com/grafana/ckit/advertise"
 	"github.com/grafana/ckit/peer"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/model"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 	"go.opentelemetry.io/otel"
@@ -50,6 +51,11 @@ import (
 	_ "github.com/grafana/alloy/internal/component/all"
 )
 
+var (
+	prometheusLegacyMetricValidationScheme = "legacy"
+	prometheusUTF8MetricValidationScheme   = "utf-8"
+)
+
 func runCommand() *cobra.Command {
 	r := &alloyRun{
 		inMemoryAddr:          "alloy.internal:12345",
@@ -64,6 +70,9 @@ func runCommand() *cobra.Command {
 		clusterMaxJoinPeers:   5,
 		clusterRejoinInterval: 60 * time.Second,
 		disableSupportBundle:  false,
+		// For backwards compatibility - use the LegacyValidation of Prometheus metrics name. This is a global variable
+		// setting that has changed upstream. See https://github.com/prometheus/common/pull/724.
+		prometheusMetricNameValidationScheme: prometheusLegacyMetricValidationScheme,
 	}
 
 	cmd := &cobra.Command{
@@ -155,38 +164,40 @@ depending on the nature of the reload error.
 	cmd.Flags().StringVar(&r.storagePath, "storage.path", r.storagePath, "Base directory where components can store data")
 	cmd.Flags().Var(&r.minStability, "stability.level", fmt.Sprintf("Minimum stability level of features to enable. Supported values: %s", strings.Join(featuregate.AllowedValues(), ", ")))
 	cmd.Flags().BoolVar(&r.enableCommunityComps, "feature.community-components.enabled", r.enableCommunityComps, "Enable community components.")
+	cmd.Flags().StringVar(&r.prometheusMetricNameValidationScheme, "feature.prometheus.metric-validation-scheme", prometheusLegacyMetricValidationScheme, fmt.Sprintf("Prometheus metric validation scheme to use. Supported values: %q, %q. NOTE: this is an experimental flag and may be removed in future releases.", prometheusLegacyMetricValidationScheme, prometheusUTF8MetricValidationScheme))
 
 	addDeprecatedFlags(cmd)
 	return cmd
 }
 
 type alloyRun struct {
-	inMemoryAddr                 string
-	httpListenAddr               string
-	storagePath                  string
-	minStability                 featuregate.Stability
-	uiPrefix                     string
-	enablePprof                  bool
-	disableReporting             bool
-	clusterEnabled               bool
-	clusterNodeName              string
-	clusterAdvAddr               string
-	clusterJoinAddr              string
-	clusterDiscoverPeers         string
-	clusterAdvInterfaces         []string
-	clusterRejoinInterval        time.Duration
-	clusterMaxJoinPeers          int
-	clusterName                  string
-	clusterEnableTLS             bool
-	clusterTLSCAPath             string
-	clusterTLSCertPath           string
-	clusterTLSKeyPath            string
-	clusterTLSServerName         string
-	configFormat                 string
-	configBypassConversionErrors bool
-	configExtraArgs              string
-	enableCommunityComps         bool
-	disableSupportBundle         bool
+	inMemoryAddr                         string
+	httpListenAddr                       string
+	storagePath                          string
+	minStability                         featuregate.Stability
+	uiPrefix                             string
+	enablePprof                          bool
+	disableReporting                     bool
+	clusterEnabled                       bool
+	clusterNodeName                      string
+	clusterAdvAddr                       string
+	clusterJoinAddr                      string
+	clusterDiscoverPeers                 string
+	clusterAdvInterfaces                 []string
+	clusterRejoinInterval                time.Duration
+	clusterMaxJoinPeers                  int
+	clusterName                          string
+	clusterEnableTLS                     bool
+	clusterTLSCAPath                     string
+	clusterTLSCertPath                   string
+	clusterTLSKeyPath                    string
+	clusterTLSServerName                 string
+	configFormat                         string
+	configBypassConversionErrors         bool
+	configExtraArgs                      string
+	enableCommunityComps                 bool
+	disableSupportBundle                 bool
+	prometheusMetricNameValidationScheme string
 }
 
 func (fr *alloyRun) Run(cmd *cobra.Command, configPath string) error {
@@ -211,6 +222,10 @@ func (fr *alloyRun) Run(cmd *cobra.Command, configPath string) error {
 		return fmt.Errorf("building tracer: %w", err)
 	}
 
+	if err := fr.configurePrometheusMetricNameValidationScheme(l); err != nil {
+		return err
+	}
+
 	// Set the global tracer provider to catch global traces, but ideally things
 	// use the tracer provider given to them so the appropriate attributes get
 	// injected.
@@ -435,6 +450,26 @@ func (fr *alloyRun) Run(cmd *cobra.Command, configPath string) error {
 	}
 }
 
+func (fr *alloyRun) configurePrometheusMetricNameValidationScheme(l log.Logger) error {
+	switch fr.prometheusMetricNameValidationScheme {
+	case prometheusLegacyMetricValidationScheme:
+		model.NameValidationScheme = model.LegacyValidation
+	case prometheusUTF8MetricValidationScheme:
+		if err := featuregate.CheckAllowed(
+			featuregate.StabilityExperimental,
+			fr.minStability,
+			"Prometheus utf-8 metric name validation scheme",
+		); err != nil {
+			return err
+		}
+		level.Warn(l).Log("msg", "Using experimental UTF-8 Prometheus metric name validation scheme")
+		model.NameValidationScheme = model.UTF8Validation
+	default:
+		return fmt.Errorf("invalid prometheus metric name validation scheme: %q", fr.prometheusMetricNameValidationScheme)
+	}
+	return nil
+}
+
 // getEnabledComponentsFunc returns a function that gets the current enabled components
 func getEnabledComponentsFunc(f *alloy_runtime.Runtime) func() map[string]interface{} {
 	return func() map[string]interface{} {

internal/alloycli/cmd_run_test.go

@@ -0,0 +1,72 @@
+package alloycli
+
+import (
+	"testing"
+
+	"github.com/go-kit/log"
+	"github.com/prometheus/common/model"
+	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/alloy/internal/featuregate"
+)
+
+func TestConfigurePrometheusMetricNameValidationScheme(t *testing.T) {
+	tests := []struct {
+		name           string
+		run            alloyRun
+		expectedError  string
+		expectedScheme model.ValidationScheme
+	}{
+		{
+			name: "legacy validation scheme",
+			run: alloyRun{
+				prometheusMetricNameValidationScheme: prometheusLegacyMetricValidationScheme,
+				minStability:                         featuregate.StabilityGenerallyAvailable,
+			},
+			expectedScheme: model.LegacyValidation,
+		},
+		{
+			name: "utf8 validation scheme with experimental stability",
+			run: alloyRun{
+				prometheusMetricNameValidationScheme: prometheusUTF8MetricValidationScheme,
+				minStability:                         featuregate.StabilityExperimental,
+			},
+			expectedScheme: model.UTF8Validation,
+		},
+		{
+			name: "utf8 validation scheme with GA stability should fail",
+			run: alloyRun{
+				prometheusMetricNameValidationScheme: prometheusUTF8MetricValidationScheme,
+				minStability:                         featuregate.StabilityGenerallyAvailable,
+			},
+			expectedError: `Prometheus utf-8 metric name validation scheme is at stability level "experimental", which is below the minimum allowed stability level "generally-available"`,
+		},
+		{
+			name: "invalid validation scheme",
+			run: alloyRun{
+				prometheusMetricNameValidationScheme: "invalid",
+				minStability:                         featuregate.StabilityGenerallyAvailable,
+			},
+			expectedError: `invalid prometheus metric name validation scheme: "invalid"`,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			// Reset the global validation scheme before each test
+			defer func() {
+				model.NameValidationScheme = model.LegacyValidation
+			}()
+
+			err := tc.run.configurePrometheusMetricNameValidationScheme(log.NewNopLogger())
+
+			if tc.expectedError != "" {
+				require.ErrorContains(t, err, tc.expectedError)
+				return
+			}
+
+			require.NoError(t, err)
+			require.Equal(t, tc.expectedScheme, model.NameValidationScheme)
+		})
+	}
+}