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Milvus supports Kafka as a message stream, we can use the configuration option to decide to use Pulsar or Kafka on cluster mode. We provide the function KafkaEnable() to use Kafka. If you don't want to use kafka, you need to comment out the configuration. Same for Pulsar and Rocksmq. If the configuration of pulsar, kafka and rocksmq are readable. then use rocksmq in standalone mode and pulsar in cluster.

Code Block

language	yml
title	milvus.yaml

plusarkafka:
  address: localhost
  port: 6650
  maxMessageSize: 5242880
#kafka:
#  brokers:
#	- localhost:9092
#  port: 9092

Design Details

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Configuration

If we want to enable Kafka, need to config it in milvus.yaml file, Pulsar is also. when Kafka and Pulsar config at the same time, Pulsar has higher priority use.

Kafka Client SDK

Configuration

Code Block

language	yml
title	dev/docker-compose.yml

version: '3.5'

services:
  zookeeper:
    image: 'bitnami/zookeeper:3.6.3'
    ports:
      - '2181:2181'
    environment:
      - ALLOW_ANONYMOUS_LOGIN=yes
  kafka:
    image: 'bitnami/kafka:3.1.0'
    ports:
      - '9092:9092'
    environment:
      - KAFKA_BROKER_ID=0
      - KAFKA_CFG_LISTENERS=PLAINTEXT://:9092
      - KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://127.0.0.1:9092
      - KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181
      - ALLOW_PLAINTEXT_LISTENER=yes
      - KAFKA_CFG_MAX_PARTITION_FETCH_BYTES=5242880
      - KAFKA_CFG_MAX_REQUEST_SIZE=5242880
      - KAFKA_CFG_MESSAGE_MAX_BYTES=5242880
      - KAFKA_CFG_REPLICA_FETCH_MAX_BYTES=5242880
      - KAFKA_CFG_FETCH_MESSAGE_MAX_BYTES=5242880
    depends_on:
      - zookeeper

networks:
  default:
    name: milvus_dev

Kafka Client SDK

Sarama
confluent-kafka-go

We tried using sarama and confluent-kafka-go in our development and found that there was basically no difference in the producer. But there is a big difference when using consumer groupgroups.

Sarama use uses consumer group need needs to implement Sarama interfaceinterfaces. It make it is very diffcult difficult to control control and hard to seek.

confulent-kafka-go use consumer group to consume messages just a function. It is very simple to use. This function allows you to directly set the offset from which to start consumption.

Interface Implementation

Note: in order to provide a unified MQ interface, We will remove some API about Reader from MsgSream interface.

Implement Kafka consumer based on the following interface:

Code Block

title	kafka_consumer.go

package kafka

import (
	"sync"
	"time"

	"github.com/confluentinc/confluent-kafka-go/kafka"
	"github.com/milvus-io/milvus/internal/log"
	"github.com/milvus-io/milvus/internal/mq/msgstream/mqwrapper"
	"go.uber.org/zap"
)

type Consumer struct {
	c          *kafka.Consumer
	msgChannel chan mqwrapper.Message
	closeFlag  bool
	skipMsg    bool
	topicName  string
	groupID    string
	closeCh    chan struct{}
	chanOnce   sync.Once
	closeOnce  sync.Once
	wg         sync.WaitGroup
}

func newKafkaConsumer(consumer *kafka.Consumer, topicName string, groupID string) *Consumer {
	msgChannel := make(chan mqwrapper.Message, 1)
	closeCh := make(chan struct{})
	skipMsg := false

	kafkaConsumer := &Consumer{c: consumer,
		msgChannel: msgChannel,
		skipMsg:    skipMsg,
		topicName:  topicName,
		groupID:    groupID,
		closeCh:    closeCh,
	}

	return kafkaConsumer
}

func (kc *Consumer) Subscription() string {
	return kc.groupID
}

// Chan provides a channel to read consumed message.
// There are some illustrations need to clarify,
// 1.confluent-kafka-go recommend us to use function-based consumer,
// channel-based consumer API had already deprecated, see more details
// https://github.com/confluentinc/confluent-kafka-go.
//
// 2.This API of other MQ return channel directly, but it depends on
// readMessage firstly which means it be always triggered within select-case
// invocation. However, it still works well, because it covers all messages
// consume situation: start from the earliest or latest position to keep consume;
// start from a seek position to specified end position.
func (kc *Consumer) Chan() <-chan mqwrapper.Message {
	if kc.skipMsg {
		msg := kc.readMessage()
		if msg != nil {
			kc.skipMsg = false
		}
	}

	msg := kc.readMessage()

	if msg != nil {
		kc.msgChannel <- &kafkaMessage{msg: msg}
	} else {
		kc.msgChannel <- nil
	}

	return kc.msgChannel
}

func (kc *Consumer) readMessage() *kafka.Message {
	msg, err := kc.c.ReadMessage(1 * time.Second)
	if err != nil {
		if err.(kafka.Error).Code() != kafka.ErrTimedOut {
			log.Error("read msg failed", zap.Any("topic", kc.topicName), zap.String("groupID", kc.groupID), zap.Error(err))
		}
		return nil
	}
	return msg
}

func (kc *Consumer) Seek(id mqwrapper.MessageID, inclusive bool) error {
	offset := kafka.Offset(id.(*kafkaID).messageID)
	log.Debug("kafka consumer seek ", zap.String("topic name", kc.topicName),
		zap.Any("Msg offset", offset), zap.Bool("inclusive", inclusive))

	//There is need to invoke Unassign before Assign or seek twice will fail
	//on the same topic and partition.
	err := kc.c.Unassign()
	if err != nil {
		log.Error("kafka consumer unassign failed ", zap.String("topic name", kc.topicName), zap.Any("Msg offset", offset), zap.Error(err))
		return err
	}

	err = kc.c.Assign([]kafka.TopicPartition{{Topic: &kc.topicName, Partition: mqwrapper.DefaultPartitionIdx, Offset: offset}})
	if err != nil {
		log.Error("kafka consumer assign failed ", zap.String("topic name", kc.topicName), zap.Any("Msg offset", offset), zap.Error(err))
		return err
	}

	// If seek timeout is not 0 the call twice will return error state RD_KAFKA_RESP_ERR__STATE.
	// if the timeout is 0 it will initiate the seek  but return immediately without any error reporting
	kc.skipMsg = !inclusive
	return kc.c.Seek(kafka.TopicPartition{
		Topic:     &kc.topicName,
		Partition: mqwrapper.DefaultPartitionIdx,
		Offset:    offset}, 0)
}

func (kc *Consumer) Ack(message mqwrapper.Message) {
	kc.c.Commit()
}

func (kc *Consumer) GetLatestMsgID() (mqwrapper.MessageID, error) {
	_, high, err := kc.c.QueryWatermarkOffsets(kc.topicName, mqwrapper.DefaultPartitionIdx, -1)
	if err != nil {
		return nil, err
	}

	// Current high value is next offset of the latest message ID, in order to keep
	// semantics consistency with the latest message ID, the high value need to move forward.
	if high > 0 {
		high = high - 1
	}

	return &kafkaID{messageID: high}, nil
}

func (kc *Consumer) Close() {
	log.Debug("close kafka consumer", zap.Any("topic", kc.topicName), zap.String("groupID", kc.groupID))
	kc.closeOnce.Do(func() {
		kc.c.Unsubscribe()
		kc.c.Close()
		close(kc.closeCh)
	})
}

Code Block

title	kafka_producer.go

package kafka

import (
	"context"
	"sync"

	"github.com/confluentinc/confluent-kafka-go/kafka"
	"github.com/milvus-io/milvus/internal/mq/msgstream/mqwrapper"
)

type kafkaProducer struct {
	p            *kafka.Producer
	topic        string
	deliveryChan chan kafka.Event
	closeOnce    sync.Once
}

func (kp *kafkaProducer) Topic() string {
	return kp.topic
}

func (kp *kafkaProducer) Send(ctx context.Context, message *mqwrapper.ProducerMessage) (mqwrapper.MessageID, error) {
	err := kp.p.Produce(&kafka.Message{
		TopicPartition: kafka.TopicPartition{Topic: &kp.topic, Partition: mqwrapper.DefaultPartitionIdx},
		Value:          message.Payload,
	}, kp.deliveryChan)

	if err != nil {
		return nil, err
	}

	e := <-kp.deliveryChan
	m := e.(*kafka.Message)
	if m.TopicPartition.Error != nil {
		return nil, m.TopicPartition.Error
	}

	kp.p.Flush(5000)
	return &kafkaID{messageID: int64(m.TopicPartition.Offset)}, nil
}

func (kp *kafkaProducer) Close() {
	kp.closeOnce.Do(func() {
		kp.p.Close()
		close(kp.deliveryChan)
	})
}

Deployments

is the interface that provides operations of a consumer
type Consumer interface {
	// returns the subscription for the consumer
	Subscription() string

	// Message channel
	Chan() <-chan Message

	// Seek to the uniqueID position
	Seek(MessageID, bool) error //nolint:govet

	// Ack make sure that msg is received
	Ack(Message)

	// Close consumer
	Close()

	// GetLatestMsgID return the latest message ID
	GetLatestMsgID() (MessageID, error)
}

Implement Kafka producer based on the following interface:

Code Block

title	kafka_producer.go

// Producer is the interface that provides operations of producer
type Producer interface {
	// return the topic which producer is publishing to
	//Topic() string

	// publish a message
	Send(ctx context.Context, message *ProducerMessage) (MessageID, error)

	Close()
}

on the other hand, we must provide a configurable ability for MQ clients, so SetParams API will be replaced by Init API.

Code Block

title	mq_factory.go

type Factory interface {
	#SetParams(params map[string]interface{}) error
	Init(params *paramtable.ComponentParam) error
}

Deployments

standalone

docker

Code Block

language	yml
title	dev/docker-compose.yml

version: '3.5'

services:
  zookeeper:
    image: 'bitnami/zookeeper:3.6.3'
    ports:
      - '2181:2181'
    environment:
      - ALLOW_ANONYMOUS_LOGIN=yes
  kafka:
    image: 'bitnami/kafka:3.1.0'
    ports:
      - '9092:9092'
    environment:
      - KAFKA_BROKER_ID=0
      - KAFKA_CFG_LISTENERS=PLAINTEXT://:9092
      - KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://127.0.0.1:9092
      - KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181
      - ALLOW_PLAINTEXT_LISTENER=yes
      - KAFKA_CFG_MAX_PARTITION_FETCH_BYTES=5242880
      - KAFKA_CFG_MAX_REQUEST_SIZE=5242880
      - KAFKA_CFG_MESSAGE_MAX_BYTES=5242880
      - KAFKA_CFG_REPLICA_FETCH_MAX_BYTES=5242880
      - KAFKA_CFG_FETCH_MESSAGE_MAX_BYTES=5242880
    depends_on:
      - zookeeper

networks:
  default:
    name: milvus_dev

standalone

docker

Cluster
- Helm Chart
- Operator

...

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