分散システムにおけるアプリケーションと課題: Golang の役割と限界

// 服务注册
func Register(serviceName, serviceAddr string) error {
    client, err := clientv3.New(clientv3.Config{
        Endpoints:   endpoints,
        DialTimeout: 5 * time.Second,
    })
    if err != nil {
        return err
    }
    defer client.Close()

    lease := clientv3.NewLease(client)

    resp, err := lease.Grant(context.Background(), 10)
    if err != nil {
        return err
    }

    _, err = client.Put(context.TODO(), "/test-service/"+serviceName+"/"+serviceAddr, "", clientv3.WithLease(resp.ID))
    if err != nil {
        return err
    }

    keepAliveChan, err := lease.KeepAlive(context.Background(), resp.ID)
    if err != nil {
        return err
    }
    go func() {
        for {
            select {
            case keepAliveResponse := <-keepAliveChan:
                if keepAliveResponse == nil {
                    // keepAlive失败，可以判定服务已经下线
                    fmt.Println("service ["+serviceName+"] offline")
                    return
                }
            }
        }
    }()

    return nil
}

// 服务发现
func Discovery(serviceName string) ([]string, error) {
    client, err := clientv3.New(clientv3.Config{
        Endpoints:   endpoints,
        DialTimeout: 5 * time.Second,
    })
    if err != nil {
        return nil, err
    }
    defer client.Close()

    resp, err := client.Get(context.Background(), "/test-service/"+serviceName+"/", clientv3.WithPrefix())
    if err != nil {
        return nil, err
    }

    addrs := make([]string, 0)
    for _, kv := range resp.Kvs {
        addrs = append(addrs, string(kv.Value))
    }

    return addrs, nil
}

// 消息生产
func Producer(){
    config := sarama.NewConfig()
    config.Producer.RequiredAcks = sarama.WaitForAll
    config.Producer.Retry.Max = 3
    config.Producer.Return.Successes = true

    producer, err := sarama.NewSyncProducer([]string{"localhost:9092"}, config)
    if err != nil {
        fmt.Println("producer close,err:", err)
        return
    }
    defer producer.Close()
    msg := &sarama.ProducerMessage{}
    msg.Topic = "test"
    msg.Value = sarama.StringEncoder("hello World!")
    _, _, err = producer.SendMessage(msg)
    if err != nil {
        fmt.Println("send message failed,err:", err)
        return
    }
    fmt.Println("send message success")
}

// 消息消费
func Consumer(){
    config := sarama.NewConfig()
    config.Consumer.Group = "test-group"
    config.Consumer.Return.Errors = true

    consumer, err := sarama.NewConsumer([]string{"localhost:9092"}, config)
    if err != nil {
        fmt.Println("consumer close,err:", err)
        return
    }
    defer consumer.Close()

    partitionList, err := consumer.Partitions("test")
    if err != nil {
        fmt.Println("Failed to get the list of partitions,err:", err)
        return
    }

    for partition := range partitionList {
        pc, err := consumer.ConsumePartition("test", int32(partition), sarama.OffsetOldest)
        if err != nil {
            fmt.Printf("Failed to start consumer for partition %d,err:%s
", partition, err)
            continue
        }
        defer pc.AsyncClose()

        for msg := range pc.Messages() {
            fmt.Printf("Partition:%d Offset:%d Key:%v Value:%v
",
                msg.Partition, msg.Offset, msg.Key, string(msg.Value))
        }
    }
}

// 数据库查询
func QueryDB(){
    db, err := sqlx.Open("mysql", "root:password@tcp(localhost:3306)/test")
    if err != nil {
        fmt.Println("Open MySQL has error :", err.Error())
    }
    defer db.Close()
    sqlStr := `SELECT user_id, username FROM users WHERE age = ?`
    rows, err := db.Query(sqlStr, 18)
    if err != nil {
        fmt.Println("Query data has error :", err.Error())
    }
    defer rows.Close()
    for rows.Next() {
        var userId int
        var username string
        rows.Scan(&userId, &username)
        fmt.Println("userId is : ", userId)
        fmt.Println("username is :", username)
    }
}

// 数据库更新
func UpdateDB(){
    db, err := sqlx.Open("mysql", "root:password@tcp(localhost:3306)/test")
    if err != nil {
        fmt.Println("Open MySQL has error :", err.Error())
    }
    defer db.Close()
    sqlStr := `UPDATE users SET username = ? WHERE user_id = ?`
    _, err = db.Exec(sqlStr, "newUserName", 1001)
    if err != nil {
        fmt.Println("Exec update has error:", err.Error())
    }
}