Add ZMQ connection retry configuration

README.md

@@ -122,6 +122,7 @@ For more details see the <a href="https://docs.vllm.ai/en/stable/getting_started
 - `tokenizers-cache-dir`: the directory for caching tokenizers
 - `hash-seed`: seed for hash generation (if not set, is read from PYTHONHASHSEED environment variable)
 - `zmq-endpoint`: ZMQ address to publish events
+- `zmq-max-connect-attempts`: the maximum number of ZMQ connection attempts. defaults to 0. maximum: 10
 - `event-batch-size`: the maximum number of kv-cache events to be sent together, defaults to 16
 - `fake-metrics`: represents a predefined set of metrics to be sent to Prometheus as a substitute for the actual data. When specified, only these fake metrics will be reported — real metrics and fake metrics will never be reported simultaneously. The set should include values for 
     - `running-requests`

manifests/invalid-config.yaml

@@ -0,0 +1,9 @@
+port: 8001
+model: "Qwen/Qwen2-0.5B"
+max-num-seqs: 5
+mode: "random"
+time-to-first-token: 2000
+inter-token-latency: 1000
+kv-cache-transfer-latency: 100
+seed: 100100100
+zmq-max-connect-attempts: -111

pkg/common/config.go

@@ -126,6 +126,8 @@ type Configuration struct {
 
 	// ZMQEndpoint is the ZMQ address to publish events, the default value is tcp://localhost:5557
 	ZMQEndpoint string `yaml:"zmq-endpoint"`
+	// ZMQMaxConnectAttempts defines the maximum number (10) of retries when ZMQ connection fails
+	ZMQMaxConnectAttempts uint `yaml:"zmq-max-connect-attempts"`
 	// EventBatchSize is the maximum number of kv-cache events to be sent together, defaults to 16
 	EventBatchSize int `yaml:"event-batch-size"`
 
@@ -354,6 +356,9 @@ func (c *Configuration) validate() error {
 	if c.EventBatchSize < 1 {
 		return errors.New("event batch size cannot less than 1")
 	}
+	if c.ZMQMaxConnectAttempts > 10 {
+		return errors.New("zmq retries times cannot be more than 10")
+	}
 
 	if c.FakeMetrics != nil {
 		if c.FakeMetrics.RunningRequests < 0 || c.FakeMetrics.WaitingRequests < 0 {
@@ -415,6 +420,7 @@ func ParseCommandParamsAndLoadConfig() (*Configuration, error) {
 	f.StringVar(&config.TokenizersCacheDir, "tokenizers-cache-dir", config.TokenizersCacheDir, "Directory for caching tokenizers")
 	f.StringVar(&config.HashSeed, "hash-seed", config.HashSeed, "Seed for hash generation (if not set, is read from PYTHONHASHSEED environment variable)")
 	f.StringVar(&config.ZMQEndpoint, "zmq-endpoint", config.ZMQEndpoint, "ZMQ address to publish events")
+	f.UintVar(&config.ZMQMaxConnectAttempts, "zmq-max-connect-attempts", config.ZMQMaxConnectAttempts, "Maximum number of times to retry ZMQ requests")
 	f.IntVar(&config.EventBatchSize, "event-batch-size", config.EventBatchSize, "Maximum number of kv-cache events to be sent together")
 
 	// These values were manually parsed above in getParamValueFromArgs, we leave this in order to get these flags in --help

pkg/common/config_test.go

@@ -103,12 +103,14 @@ var _ = Describe("Simulator configuration", func() {
 		"{\"name\":\"lora4\",\"path\":\"/path/to/lora4\"}",
 	}
 	c.EventBatchSize = 5
+	c.ZMQMaxConnectAttempts = 1
 	test = testCase{
 		name: "config file with command line args",
 		args: []string{"cmd", "--model", model, "--config", "../../manifests/config.yaml", "--port", "8002",
 			"--served-model-name", "alias1", "alias2", "--seed", "100",
 			"--lora-modules", "{\"name\":\"lora3\",\"path\":\"/path/to/lora3\"}", "{\"name\":\"lora4\",\"path\":\"/path/to/lora4\"}",
 			"--event-batch-size", "5",
+			"--zmq-max-connect-attempts", "1",
 		},
 		expectedConfig: c,
 	}
@@ -121,6 +123,7 @@ var _ = Describe("Simulator configuration", func() {
 	c.LoraModulesString = []string{
 		"{\"name\":\"lora3\",\"path\":\"/path/to/lora3\"}",
 	}
+	c.ZMQMaxConnectAttempts = 0
 	test = testCase{
 		name: "config file with command line args with different format",
 		args: []string{"cmd", "--model", model, "--config", "../../manifests/config.yaml", "--port", "8002",
@@ -377,6 +380,14 @@ var _ = Describe("Simulator configuration", func() {
 			args: []string{"cmd", "--fake-metrics", "{\"running-requests\":10,\"waiting-requests\":30,\"kv-cache-usage\":40}",
 				"--config", "../../manifests/config.yaml"},
 		},
+		{
+			name: "invalid (negative) zmq-max-connect-attempts for argument",
+			args: []string{"cmd", "zmq-max-connect-attempts", "-1", "--config", "../../manifests/config.yaml"},
+		},
+		{
+			name: "invalid (negative) zmq-max-connect-attempts for config file",
+			args: []string{"cmd", "--config", "../../manifests/invalid-config.yaml"},
+		},
 	}
 
 	for _, test := range invalidTests {

pkg/common/publisher.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"sync/atomic"
+	"time"
 
 	zmq "github.com/pebbe/zmq4"
 	"github.com/vmihailenco/msgpack/v5"
@@ -38,24 +39,34 @@ type Publisher struct {
 
 // NewPublisher creates a new ZMQ publisher.
 // endpoint is the ZMQ address to bind to (e.g., "tcp://*:5557").
-func NewPublisher(endpoint string) (*Publisher, error) {
+// retries is the maximum number of connection attempts.
+func NewPublisher(endpoint string, retries uint) (*Publisher, error) {
 	socket, err := zmq.NewSocket(zmq.PUB)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create ZMQ PUB socket: %w", err)
 	}
 
-	if err := socket.Connect(endpoint); err != nil {
-		errClose := socket.Close()
-		return nil, errors.Join(
-			fmt.Errorf("failed to connect to %s: %w", endpoint, err),
-			errClose,
-		)
+	// Retry connection with specified retry times and intervals
+	for i := uint(0); i <= retries; i++ {
+		err = socket.Connect(endpoint)
+		if err == nil {
+			return &Publisher{
+				socket:   socket,
+				endpoint: endpoint,
+			}, nil
+		}
+
+		// If not the last attempt, wait before retrying
+		if i < retries {
+			time.Sleep(1 * time.Second)
+		}
 	}
 
-	return &Publisher{
-		socket:   socket,
-		endpoint: endpoint,
-	}, nil
+	errClose := socket.Close()
+	return nil, errors.Join(
+		fmt.Errorf("failed to connect to %s after %d retries: %w", endpoint, retries+1, err),
+		errClose,
+	)
 }
 
 // PublishEvent publishes a KV cache event batch to the ZMQ topic.

pkg/common/publisher_test.go

@@ -33,6 +33,7 @@ const (
 	subEndpoint = "tcp://*:5557"
 	pubEndpoint = "tcp://localhost:5557"
 	data        = "Hello"
+	retries     = 0
 )
 
 var _ = Describe("Publisher", func() {
@@ -50,7 +51,7 @@ var _ = Describe("Publisher", func() {
 
 		time.Sleep(100 * time.Millisecond)
 
-		pub, err := NewPublisher(pubEndpoint)
+		pub, err := NewPublisher(pubEndpoint, retries)
 		Expect(err).NotTo(HaveOccurred())
 
 		ctx, cancel := context.WithCancel(context.Background())
@@ -78,4 +79,40 @@ var _ = Describe("Publisher", func() {
 		Expect(err).NotTo(HaveOccurred())
 		Expect(payload).To(Equal(data))
 	})
+	It("should fail when connection attempts exceed maximum retries", func() {
+		// Use invalid address format, which will cause connection to fail
+		invalidEndpoint := "invalid-address-format"
+
+		pub, err := NewPublisher(invalidEndpoint, 2)
+		Expect(err).To(HaveOccurred())
+		Expect(err.Error()).To(ContainSubstring("failed to connect"))
+		Expect(err.Error()).To(ContainSubstring("after 3 retries")) // 2 retries = 3 total attempts
+
+		if pub != nil {
+			//nolint
+			pub.Close()
+		}
+	})
+	It("should retry connection successfully", func() {
+		// Step 1: Try to connect to a temporarily non-existent service
+		// This will trigger the retry mechanism
+		go func() {
+			// Delay starting the server to simulate service recovery
+			time.Sleep(2 * time.Second)
+
+			// Start subscriber as server
+			sub, err := zmq.NewSocket(zmq.SUB)
+			Expect(err).NotTo(HaveOccurred())
+			//nolint
+			defer sub.Close()
+			err = sub.Bind(subEndpoint)
+			Expect(err).NotTo(HaveOccurred())
+		}()
+
+		// Step 2: Publisher will retry connection and eventually succeed
+		pub, err := NewPublisher(pubEndpoint, 5) // 5 retries
+		Expect(err).NotTo(HaveOccurred())        // Should eventually succeed
+		//nolint
+		defer pub.Close()
+	})
 })

pkg/kv-cache/block_cache.go

@@ -48,7 +48,7 @@ func newBlockCache(config *common.Configuration, logger logr.Logger) (*blockCach
 	// TODO read size of channel from config
 	eChan := make(chan EventData, 10000)
 
-	publisher, err := common.NewPublisher(config.ZMQEndpoint)
+	publisher, err := common.NewPublisher(config.ZMQEndpoint, config.ZMQMaxConnectAttempts)
 	if err != nil {
 		return nil, err
 	}

pkg/kv-cache/kv_cache_test.go

@@ -201,11 +201,12 @@ var _ = Describe("KV cache", Ordered, func() {
 				time.Sleep(300 * time.Millisecond)
 
 				config := &common.Configuration{
-					Port:           1234,
-					Model:          "model",
-					KVCacheSize:    test.cacheSize,
-					ZMQEndpoint:    pubEndpoint,
-					EventBatchSize: 1,
+					Port:                  1234,
+					Model:                 "model",
+					KVCacheSize:           test.cacheSize,
+					ZMQEndpoint:           pubEndpoint,
+					ZMQMaxConnectAttempts: 3,
+					EventBatchSize:        1,
 				}
 
 				sub, topic := createSub(config)
@@ -304,10 +305,11 @@ var _ = Describe("KV cache", Ordered, func() {
 
 		It("should send events correctly", func() {
 			config := &common.Configuration{
-				Port:        1234,
-				Model:       "model",
-				KVCacheSize: 4,
-				ZMQEndpoint: pubEndpoint,
+				Port:                  1234,
+				Model:                 "model",
+				KVCacheSize:           4,
+				ZMQEndpoint:           pubEndpoint,
+				ZMQMaxConnectAttempts: 3,
 			}
 
 			sub, topic := createSub(config)
@@ -413,10 +415,11 @@ var _ = Describe("KV cache", Ordered, func() {
 		for _, testCase := range testCases {
 			It(testCase.name, func() {
 				config := common.Configuration{
-					Port:        1234,
-					Model:       "model",
-					KVCacheSize: testCase.cacheSize,
-					ZMQEndpoint: pubEndpoint,
+					Port:                  1234,
+					Model:                 "model",
+					KVCacheSize:           testCase.cacheSize,
+					ZMQEndpoint:           pubEndpoint,
+					ZMQMaxConnectAttempts: 3,
 				}
 				blockCache, err := newBlockCache(&config, GinkgoLogr)
 				Expect(err).NotTo(HaveOccurred())