Add explicit token-producer backend selector

config/charts/README.md

@@ -316,7 +316,7 @@ router:
 
 Runs a tokenizer sidecar that EPP queries to tokenize incoming requests, enabling precise, token-count-aware routing policies (e.g., precise prefix-cache matching).
 
-The sidecar runs vLLM's `vllm launch render <modelName>` and exposes `/v1/completions/render` and `/v1/chat/completions/render` over loopback HTTP. Wire EPP to it via `router.epp.pluginsCustomConfig` with `type: token-producer` and `vllm:`.
+The sidecar runs vLLM's `vllm launch render <modelName>` and exposes `/v1/completions/render` and `/v1/chat/completions/render` over loopback HTTP. Wire EPP to it via `router.epp.pluginsCustomConfig` with `type: token-producer`, `backend: vllm`, and `vllm:`.
 
 #### Tokenizer Sidecar Parameters
 
@@ -420,8 +420,8 @@ spec:
 
 **Step 2 — point EPP at the socket.** Configure the tokenizer plugin via
 `router.epp.pluginsCustomConfig` (the chart writes this into the EPP config
-mounted at `/config`). Select the deprecated UDS backend with
-`udsTokenizerConfig`:
+mounted at `/config`). Select the deprecated UDS backend with `backend: uds`
+and point it at the socket with `udsTokenizerConfig`:
 
 ```yaml
 router:
@@ -431,6 +431,7 @@ router:
         plugins:
           - type: token-producer
             parameters:
+              backend: uds
               modelName: "Qwen/Qwen3-32B"
               udsTokenizerConfig:
                 socketFile: /tmp/tokenizer/tokenizer-uds.socket

deploy/config/epp-mm-embeddings-cache-config.yaml

@@ -4,6 +4,7 @@ kind: EndpointPickerConfig
 plugins:
   - type: token-producer
     parameters:
+      backend: vllm
       modelName: hf-repo/model-name           # set to the model used in the vLLM deployment
       vllm:
         url: http://localhost:8000

deploy/config/epp-precise-prefix-cache-config.yaml

@@ -5,6 +5,7 @@ kind: EndpointPickerConfig
 plugins:
   - type: token-producer
     parameters:
+      backend: vllm
       modelName: hf-repo/model-name           # set to the model used in the vLLM deployment
       vllm:
         url: http://localhost:8000

deploy/config/sim-epp-kvcache-config.yaml

@@ -5,6 +5,7 @@ kind: EndpointPickerConfig
 plugins:
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: TinyLlama/TinyLlama-1.1B-Chat-v1.0  # replace to use a different model
     vllm:
       url: http://localhost:8000

deploy/config/sim-epp-tokenizer-vllm-http-config.yaml

@@ -7,6 +7,7 @@ kind: EndpointPickerConfig
 plugins:
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: "${MODEL_NAME}"
     vllm:
       url: "http://localhost:8000"

pkg/epp/framework/plugins/requestcontrol/dataproducer/tokenizer/README.md

@@ -21,6 +21,8 @@ upstream list shape, sorted by placeholder offset.
 
 Backend selection:
 
+- Set **`backend: estimate|vllm|uds`** to select a backend explicitly.
+  When omitted, the plugin keeps the legacy inference rules below.
 - **`estimate`** (default): tokenizer-free byte-packing — no model, no service.
   Selected when no backend is set, and auto-created by the framework for any
   config whose plugins consume `TokenizedPrompt` (prefix cache, context-length,
@@ -48,7 +50,8 @@ Backend selection:
 
 | Parameter        | Default                 | Description                                                       |
 | ---------------- | ----------------------- | ----------------------------------------------------------------- |
-| `modelName`      | – (required for `vllm`) | Model whose tokenizer should be loaded / sent in render requests. |
+| `backend`        | inferred                | Explicit backend selector: `estimate`, `vllm`, or `uds`.          |
+| `modelName`      | – (required for `vllm`/`uds`) | Model whose tokenizer should be loaded / sent in render requests. |
 | `vllm.url`       | `http://localhost:8000` | Base URL of the vLLM render endpoint (no trailing slash).         |
 | `vllm.timeout`   | `5s`                    | Per-request timeout for text-only requests.                       |
 | `vllm.mmTimeout` | `30s`                   | Per-request timeout for multimodal requests.                      |
@@ -93,6 +96,7 @@ Plugin config — sidecar (loopback):
 ```yaml
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: "${MODEL_NAME}"
     vllm:
       url: "http://localhost:8000"       # optional; this is the default
@@ -103,6 +107,7 @@ Plugin config — dedicated render Service:
 ```yaml
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: "${MODEL_NAME}"
     vllm:
       url: "http://vllm-render.default.svc.cluster.local:8000"
@@ -122,6 +127,7 @@ Before:
 ```yaml
 - type: token-producer
   parameters:
+    backend: uds
     modelName: "${MODEL_NAME}"
     udsTokenizerConfig:
       socketFile: /tmp/tokenizer/tokenizer-uds.socket
@@ -132,6 +138,7 @@ After:
 ```yaml
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: "${MODEL_NAME}"
     vllm:
       url: "http://localhost:8000"   # or a shared render Service

pkg/epp/framework/plugins/requestcontrol/dataproducer/tokenizer/tokenizer.go

@@ -58,22 +58,30 @@ const (
 
 var TokenizedPromptDataKey = plugin.NewDataKey(tokenizedPromptKeyID, PluginType)
 
+type tokenizerBackend string
+
+const (
+	tokenizerBackendEstimate tokenizerBackend = "estimate"
+	tokenizerBackendVLLM     tokenizerBackend = "vllm"
+	tokenizerBackendUDS      tokenizerBackend = "uds"
+)
+
 // tokenizerPluginConfig holds the configuration for the tokenizer plugin.
-//
-// Backend selection: `vllm` or `modelName` selects the vLLM HTTP /render
-// backend; `udsTokenizerConfig` selects the deprecated gRPC-over-UDS backend;
-// `estimate` selects the tokenizer-free byte-packing backend, which is also the
-// zero-config default when no backend is set.
 type tokenizerPluginConfig struct {
+	// Backend explicitly selects "estimate", "vllm", or "uds". When omitted,
+	// the plugin preserves legacy behavior by inferring the backend from
+	// existing config fields.
+	Backend tokenizerBackend `json:"backend,omitempty"`
 	// TokenizerConfig configures the deprecated gRPC-over-UDS backend.
 	//
 	// Deprecated: the UDS tokenizer backend is deprecated and will be removed
 	// in a future release. Migrate to the `vllm` HTTP /render backend.
 	TokenizerConfig tokenization.UdsTokenizerConfig `json:"udsTokenizerConfig,omitempty"`
 	// VLLM configures the vLLM /render backend.
 	VLLM *vllmConfig `json:"vllm,omitempty"`
-	// Estimate selects the tokenizer-free byte-packing backend; mutually
-	// exclusive with 'vllm'/'udsTokenizerConfig' and needs no 'modelName'.
+	// Estimate configures the tokenizer-free byte-packing backend. When
+	// backend is omitted, it selects the estimate backend and needs no
+	// 'modelName'.
 	Estimate *estimateConfig `json:"estimate,omitempty"`
 	// ModelName is the name of the model whose tokenizer should be loaded.
 	ModelName string `json:"modelName"`
@@ -128,29 +136,67 @@ func PluginFactory(name string, rawParameters *json.Decoder, handle plugin.Handl
 		}
 	}
 
-	estimate := config.Estimate != nil
-	uds := config.TokenizerConfig.IsEnabled()
-	vllm := config.VLLM != nil || config.ModelName != ""
-	if (estimate && (uds || vllm)) || (uds && vllm) {
-		return nil, fmt.Errorf("invalid configuration for '%s' plugin: only one of 'estimate', 'vllm', or 'udsTokenizerConfig' may be set", PluginType)
+	p, err := NewPlugin(handle.Context(), name, &config)
+	if err != nil {
+		return nil, err
 	}
-	// modelName is required only by the real-tokenizer backends; the zero-config
-	// path selects the estimate backend, which needs none.
-	if (uds || vllm) && config.ModelName == "" {
-		return nil, fmt.Errorf("invalid configuration for '%s' plugin: 'modelName' must be specified", PluginType)
+
+	return p, nil
+}
+
+func (config *tokenizerPluginConfig) validateAndSelectBackend() (tokenizerBackend, error) {
+	selected, err := config.selectBackend()
+	if err != nil {
+		return "", err
 	}
-	if config.Estimate != nil && config.Estimate.Image != nil {
-		if m := config.Estimate.Image.Mode; m != "" && m != imageModeDynamic && m != imageModeStatic {
-			return nil, fmt.Errorf("invalid configuration for '%s' plugin: estimate.image.mode must be %q or %q", PluginType, imageModeDynamic, imageModeStatic)
+
+	switch selected {
+	case tokenizerBackendVLLM:
+		if config.ModelName == "" {
+			return "", fmt.Errorf("invalid configuration for '%s' plugin: 'modelName' must be specified", PluginType)
+		}
+	case tokenizerBackendUDS:
+		if config.ModelName == "" {
+			return "", fmt.Errorf("invalid configuration for '%s' plugin: 'modelName' must be specified", PluginType)
+		}
+		if !config.TokenizerConfig.IsEnabled() {
+			return "", fmt.Errorf("invalid configuration for '%s' plugin: 'udsTokenizerConfig' must be specified when backend is %q", PluginType, tokenizerBackendUDS)
+		}
+	case tokenizerBackendEstimate:
+		if config.Estimate != nil && config.Estimate.Image != nil {
+			if m := config.Estimate.Image.Mode; m != "" && m != imageModeDynamic && m != imageModeStatic {
+				return "", fmt.Errorf("invalid configuration for '%s' plugin: estimate.image.mode must be %q or %q", PluginType, imageModeDynamic, imageModeStatic)
+			}
 		}
 	}
 
-	p, err := NewPlugin(handle.Context(), name, &config)
-	if err != nil {
-		return nil, err
+	return selected, nil
+}
+
+func (config *tokenizerPluginConfig) selectBackend() (tokenizerBackend, error) {
+	if config.Backend != "" {
+		switch config.Backend {
+		case tokenizerBackendEstimate, tokenizerBackendVLLM, tokenizerBackendUDS:
+			return config.Backend, nil
+		default:
+			return "", fmt.Errorf("invalid configuration for '%s' plugin: backend must be one of %q, %q, or %q", PluginType, tokenizerBackendEstimate, tokenizerBackendVLLM, tokenizerBackendUDS)
+		}
 	}
 
-	return p, nil
+	estimate := config.Estimate != nil
+	uds := config.TokenizerConfig.IsEnabled()
+	vllm := config.VLLM != nil || config.ModelName != ""
+	if (estimate && (uds || vllm)) || (uds && vllm) {
+		return "", fmt.Errorf("invalid configuration for '%s' plugin: only one of 'estimate', 'vllm', or 'udsTokenizerConfig' may be set", PluginType)
+	}
+	switch {
+	case uds:
+		return tokenizerBackendUDS, nil
+	case vllm:
+		return tokenizerBackendVLLM, nil
+	default:
+		return tokenizerBackendEstimate, nil
+	}
 }
 
 // LegacyPluginFactory wraps PluginFactory for the deprecated `tokenizer` type
@@ -166,13 +212,20 @@ func LegacyPluginFactory(name string, rawParameters *json.Decoder, handle plugin
 	return PluginFactory(name, rawParameters, handle)
 }
 
-// NewPlugin constructs the configured backend: udsTokenizerConfig (deprecated),
-// vllm /render (selected by 'vllm' or 'modelName'), or estimate byte-packing
-// (the default when no backend is set).
+// NewPlugin constructs the configured backend. The explicit backend selector
+// wins when set; otherwise legacy config inference is used.
 func NewPlugin(ctx context.Context, name string, config *tokenizerPluginConfig) (*Plugin, error) {
+	if config == nil {
+		config = &tokenizerPluginConfig{}
+	}
+	selected, err := config.validateAndSelectBackend()
+	if err != nil {
+		return nil, err
+	}
+
 	var backend tokenInputProducer
-	switch {
-	case config.TokenizerConfig.IsEnabled():
+	switch selected {
+	case tokenizerBackendUDS:
 		log.FromContext(ctx).Info(
 			"DEPRECATION: the 'udsTokenizerConfig' parameter is deprecated and will be removed in a future release; set the 'vllm' parameter instead (see plugin README)",
 			"pluginType", PluginType,
@@ -182,7 +235,7 @@ func NewPlugin(ctx context.Context, name string, config *tokenizerPluginConfig)
 			return nil, fmt.Errorf("failed to initialize UDS tokenizer for '%s' plugin - %w", PluginType, err)
 		}
 		backend = renderBackend{tk: uds}
-	case config.VLLM != nil || config.ModelName != "":
+	case tokenizerBackendVLLM:
 		cfg := config.VLLM
 		if cfg == nil {
 			cfg = &vllmConfig{}
@@ -192,7 +245,7 @@ func NewPlugin(ctx context.Context, name string, config *tokenizerPluginConfig)
 			return nil, fmt.Errorf("failed to initialize vLLM HTTP renderer for '%s' plugin - %w", PluginType, err)
 		}
 		backend = renderBackend{tk: renderer}
-	default:
+	case tokenizerBackendEstimate:
 		backend = estimateBackend{img: newImageEstimator(config.Estimate)}
 	}
 

pkg/epp/framework/plugins/requestcontrol/dataproducer/tokenizer/tokenizer_test.go

@@ -68,6 +68,11 @@ func TestProduceTimeout(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, 45*time.Second, vp2.ProduceTimeout())
 
+	// Explicit backend selection can use vLLM's default config block.
+	vp3, err := NewPlugin(ctx, "tok", &tokenizerPluginConfig{Backend: tokenizerBackendVLLM, ModelName: "m"})
+	require.NoError(t, err)
+	assert.Equal(t, defaultHTTPRenderMMTimeout, vp3.ProduceTimeout())
+
 	// Estimate backend declares none, so the director keeps its default.
 	ep, err := NewPlugin(ctx, "tok", &tokenizerPluginConfig{Estimate: &estimateConfig{}})
 	require.NoError(t, err)
@@ -108,6 +113,29 @@ func TestPluginFactory_Validation(t *testing.T) {
 			params:    `{"estimate":{"image":{"mode":"static","static":{"staticToken":8}}}}`,
 			expectErr: false,
 		},
+		{
+			name:      "explicit estimate backend overrides legacy vllm inference",
+			params:    `{"backend":"estimate","modelName":"m","vllm":{}}`,
+			expectErr: false,
+		},
+		{
+			name:       "explicit vllm backend requires modelName",
+			params:     `{"backend":"vllm","vllm":{}}`,
+			expectErr:  true,
+			errContain: "'modelName' must be specified",
+		},
+		{
+			name:       "explicit uds backend requires tokenizer config",
+			params:     `{"backend":"uds","modelName":"m"}`,
+			expectErr:  true,
+			errContain: "'udsTokenizerConfig' must be specified",
+		},
+		{
+			name:       "invalid backend selector",
+			params:     `{"backend":"unknown"}`,
+			expectErr:  true,
+			errContain: "backend must be one of",
+		},
 		{
 			name:       "invalid estimate image mode",
 			params:     `{"estimate":{"image":{"mode":"bogus"}}}`,

test/e2e/configs_test.go

@@ -185,6 +185,7 @@ kind: EndpointPickerConfig
 plugins:
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: Qwen/Qwen2.5-1.5B-Instruct
     vllm:
       url: http://localhost:8000
@@ -217,6 +218,7 @@ kind: EndpointPickerConfig
 plugins:
 - type: token-producer
   parameters:
+    backend: vllm
     modelName: Qwen/Qwen2.5-1.5B-Instruct
     vllm:
       url: http://localhost:8000