[Flow Control] Garbage Collection for Priority Bands

pkg/epp/flowcontrol/registry/config.go

@@ -47,9 +47,10 @@ const (
 	defaultInitialShardCount int = 1
 	// defaultFlowGCTimeout is the default duration of inactivity after which an idle flow is garbage collected.
 	// This also serves as the interval for the periodic garbage collection scan.
-	// TODO:(https://github.com/kubernetes-sigs/gateway-api-inference-extension/issues/1982) revert to 5m once this GC
-	// race condition is properly resolved.
-	defaultFlowGCTimeout time.Duration = 1 * time.Hour
+	defaultFlowGCTimeout time.Duration = 5 * time.Minute
+	// defaultPriorityBandGCTimeout is the default duration of inactivity after which a dynamically provisioned
+	// priority band is garbage collected. Set to 2x flow GC timeout to ensure flows are cleaned up first.
+	defaultPriorityBandGCTimeout time.Duration = 2 * defaultFlowGCTimeout
 	// defaultEventChannelBufferSize is the default size of the buffered channel for control plane events.
 	defaultEventChannelBufferSize int = 4096
 )
@@ -133,6 +134,12 @@ type Config struct {
 	// Optional: Defaults to `defaultFlowGCTimeout` (1 hour).
 	FlowGCTimeout time.Duration
 
+	// PriorityBandGCTimeout defines the duration of inactivity after which a dynamically provisioned priority band
+	// is garbage collected. A band is considered idle when it has no flows and no buffered requests across all shards.
+	// Must be >= FlowGCTimeout to ensure flows are collected before bands.
+	// Optional: Defaults to `defaultPriorityBandGCTimeout` (10 minutes).
+	PriorityBandGCTimeout time.Duration
+
 	// EventChannelBufferSize defines the size of the buffered channel used for internal control plane events.
 	// A larger buffer can absorb larger bursts of events (e.g., from many queues becoming non-empty simultaneously)
 	// without blocking the data path, but consumes more memory.
@@ -218,6 +225,20 @@ func WithFlowGCTimeout(d time.Duration) ConfigOption {
 	}
 }
 
+// WithPriorityBandGCTimeout sets the idle priority band garbage collection timeout.
+func WithPriorityBandGCTimeout(d time.Duration) ConfigOption {
+	return func(b *configBuilder) error {
+		if d <= 0 {
+			return errors.New("priorityBandGCTimeout must be positive")
+		}
+		if b.config.FlowGCTimeout > 0 && d < b.config.FlowGCTimeout {
+			return errors.New("priorityBandGCTimeout must be >= flowGCTimeout")
+		}
+		b.config.PriorityBandGCTimeout = d
+		return nil
+	}
+}
+
 // WithPriorityBand adds a priority band configuration.
 // If a band with the same Priority already exists, it returns an error.
 func WithPriorityBand(band *PriorityBandConfig) ConfigOption {
@@ -329,6 +350,7 @@ func NewConfig(handle plugins.Handle, opts ...ConfigOption) (*Config, error) {
 			MaxBytes:               0, // no limit enforced
 			InitialShardCount:      defaultInitialShardCount,
 			FlowGCTimeout:          defaultFlowGCTimeout,
+			PriorityBandGCTimeout:  defaultPriorityBandGCTimeout,
 			EventChannelBufferSize: defaultEventChannelBufferSize,
 			PriorityBands:          make(map[int]*PriorityBandConfig),
 		},
@@ -447,6 +469,12 @@ func (c *Config) validate(checker capabilityChecker) error {
 	if c.FlowGCTimeout <= 0 {
 		return errors.New("flowGCTimeout must be positive")
 	}
+	if c.PriorityBandGCTimeout <= 0 {
+		return errors.New("priorityBandGCTimeout must be positive")
+	}
+	if c.PriorityBandGCTimeout < c.FlowGCTimeout {
+		return errors.New("priorityBandGCTimeout must be >= flowGCTimeout")
+	}
 	if c.EventChannelBufferSize <= 0 {
 		return errors.New("eventChannelBufferSize must be greater than 0")
 	}

pkg/epp/flowcontrol/registry/config_test.go

@@ -92,6 +92,7 @@ func TestNewConfig(t *testing.T) {
 			assertion: func(t *testing.T, cfg *Config) {
 				assert.Equal(t, defaultInitialShardCount, cfg.InitialShardCount, "InitialShardCount should be defaulted")
 				assert.Equal(t, defaultFlowGCTimeout, cfg.FlowGCTimeout, "FlowGCTimeout should be defaulted")
+				assert.Equal(t, defaultPriorityBandGCTimeout, cfg.PriorityBandGCTimeout, "PriorityBandGCTimeout should be defaulted")
 				assert.Equal(t, defaultEventChannelBufferSize, cfg.EventChannelBufferSize,
 					"EventChannelBufferSize should be defaulted")
 
@@ -111,13 +112,15 @@ func TestNewConfig(t *testing.T) {
 				WithInitialShardCount(10),
 				WithMaxBytes(5000),
 				WithFlowGCTimeout(1 * time.Hour),
+				WithPriorityBandGCTimeout(2 * time.Hour),
 				WithPriorityBand(mustBand(t, 1, "High")),
 			},
 			handle: newTestPluginsHandle(t),
 			assertion: func(t *testing.T, cfg *Config) {
 				assert.Equal(t, 10, cfg.InitialShardCount)
 				assert.Equal(t, uint64(5000), cfg.MaxBytes)
 				assert.Equal(t, 1*time.Hour, cfg.FlowGCTimeout)
+				assert.Equal(t, 2*time.Hour, cfg.PriorityBandGCTimeout)
 			},
 		},
 		{
@@ -187,6 +190,43 @@ func TestNewConfig(t *testing.T) {
 			handle:    newTestPluginsHandle(t),
 			expectErr: true,
 		},
+		{
+			name:      "ShouldError_WhenPriorityBandGCTimeoutIsNegative",
+			opts:      []ConfigOption{WithPriorityBandGCTimeout(-1 * time.Second)},
+			handle:    newTestPluginsHandle(t),
+			expectErr: true,
+		},
+		{
+			name: "ShouldError_WhenPriorityBandGCTimeoutLessThanFlowGCTimeout",
+			opts: []ConfigOption{
+				WithFlowGCTimeout(10 * time.Minute),
+				WithPriorityBandGCTimeout(5 * time.Minute), // Less than flow timeout
+			},
+			handle:    newTestPluginsHandle(t),
+			expectErr: true,
+		},
+		{
+			name: "ShouldSucceed_WhenPriorityBandGCTimeoutEqualToFlowGCTimeout",
+			opts: []ConfigOption{
+				WithFlowGCTimeout(10 * time.Minute),
+				WithPriorityBandGCTimeout(10 * time.Minute), // Equal is OK
+			},
+			handle: newTestPluginsHandle(t),
+			assertion: func(t *testing.T, cfg *Config) {
+				assert.Equal(t, 10*time.Minute, cfg.PriorityBandGCTimeout)
+			},
+		},
+		{
+			name: "ShouldSucceed_WhenPriorityBandGCTimeoutGreaterThanFlowGCTimeout",
+			opts: []ConfigOption{
+				WithFlowGCTimeout(5 * time.Minute),
+				WithPriorityBandGCTimeout(15 * time.Minute),
+			},
+			handle: newTestPluginsHandle(t),
+			assertion: func(t *testing.T, cfg *Config) {
+				assert.Equal(t, 15*time.Minute, cfg.PriorityBandGCTimeout)
+			},
+		},
 
 		// --- Validation Errors (Bands) ---
 		{