fix: remove deprecated flow control env var

ENABLE_EXPERIMENTAL_FLOW_CONTROL_LAYER was deprecated when GIE 1.5.0
introduced the featureGates: [flowControl] config stanza, which router
0.8.0 picked up. It was also broken: initAdmissionControl reads
r.featureGates, populated once during parseConfigurationPhaseOne, while
the env var was only ever applied afterward in parseConfigurationPhaseTwo
against rawConfig.FeatureGates. Setting it logged the deprecation warning
but silently left the EPP on the legacy admission controller.

Ahead of the 0.10.0 release, remove the env var entirely instead of
fixing it, since the config-based replacement has been available since
0.8.0. Use featureGates: [flowControl] in the EndpointPickerConfig.

Fixes #2065

Signed-off-by: elinacse <elina.gcek94@gmail.com>

Author: elinacse

cmd/epp/runner/feature_gate_test.go

@@ -18,7 +18,6 @@ package runner
 
 import (
 	"context"
-	"os"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -67,13 +66,6 @@ featureGates:
 // feature-gate map instead of hardcoding it, so this test keeps passing unchanged when the gate
 // flips to enabled-by-default (#2104) and pins that the flip actually changes the default wiring.
 func TestFlowControlFeatureGateAdmissionControlWiring(t *testing.T) {
-	// The deprecated ENABLE_EXPERIMENTAL_FLOW_CONTROL_LAYER env var appends the gate to the config
-	// during phase two; clear it so only the featureGates stanza under test drives the outcome.
-	if v, ok := os.LookupEnv(enableExperimentalFlowControlLayer); ok {
-		require.NoError(t, os.Unsetenv(enableExperimentalFlowControlLayer))
-		t.Cleanup(func() { _ = os.Setenv(enableExperimentalFlowControlLayer, v) })
-	}
-
 	boolPtr := func(b bool) *bool { return &b }
 	testCases := []struct {
 		name       string

cmd/epp/runner/runner.go

@@ -139,17 +139,9 @@ import (
 	"github.com/llm-d/llm-d-router/pkg/epp/requestcontrol"
 	"github.com/llm-d/llm-d-router/pkg/epp/scheduling"
 	runserver "github.com/llm-d/llm-d-router/pkg/epp/server"
-	"github.com/llm-d/llm-d-router/pkg/epp/util/env"
 	"github.com/llm-d/llm-d-router/version"
 )
 
-const (
-	// enableExperimentalFlowControlLayer defines the environment variable used as a feature flag for the pluggable flow
-	// control layer.
-	// DEPRECATION NOTICE - this env var will be removed in the next version as we switch to configuring the EPP using FeatureGates in the config file.
-	enableExperimentalFlowControlLayer = "ENABLE_EXPERIMENTAL_FLOW_CONTROL_LAYER"
-)
-
 var (
 	setupLog = ctrl.Log.WithName("setup")
 )
@@ -717,8 +709,6 @@ func makePodListFunc(ds datastore.Datastore) func() []types.NamespacedName {
 func (r *Runner) parseConfigurationPhaseTwo(ctx context.Context, rawConfig *configapi.EndpointPickerConfig, ds datastore.Datastore) (*config.Config, error) {
 	logger := log.FromContext(ctx)
 
-	applyDeprecatedEnvFeatureGate(enableExperimentalFlowControlLayer, "Flow Control layer", flowcontrol.FeatureGate, rawConfig)
-
 	handle := fwkplugin.NewEppHandle(ctx, makePodListFunc(ds), fwkplugin.WithMetricsRecorder(ctrlmetrics.Registry))
 	r.PluginHandle = handle
 	cfg, err := loader.InstantiateAndConfigure(rawConfig, handle, logger)
@@ -763,18 +753,6 @@ func (r *Runner) parseConfigurationPhaseTwo(ctx context.Context, rawConfig *conf
 	return cfg, nil
 }
 
-func applyDeprecatedEnvFeatureGate(envVar, featureName, featureGate string, rawConfig *configapi.EndpointPickerConfig) {
-	if _, ok := os.LookupEnv(envVar); ok {
-		setupLog.Info(fmt.Sprintf("Enabling the experimental %s using environment variables is deprecated and will be removed in next version", featureName))
-		if env.GetEnvBool(envVar, false, setupLog) {
-			if rawConfig.FeatureGates == nil {
-				rawConfig.FeatureGates = make(configapi.FeatureGates, 0)
-			}
-			rawConfig.FeatureGates = append(rawConfig.FeatureGates, featureGate)
-		}
-	}
-}
-
 func (r *Runner) configureAndStartDatalayer(ctx context.Context, cfg *datalayer.Config, mgr ctrl.Manager) error {
 	if err := r.dlRuntime.Configure(cfg, setupLog); err != nil {
 		return err