集群模式

nats的集群模式对客户端来说并不是透明的。
所以集群对发布者和订阅者都是有影响的。
发布者和订阅者都知道连接的是一个集群的服务，而不是一个单点服务,换句话说发布者订阅者都必须指明集群中各个节点的地址。
当然，发布者和订阅者可以只针对集群中的某节点发布消息和订阅消息，不过这并不是集群模式的目的。

目的

提高可用性和可伸缩性。

实现原理

可用性，多个节点，挂掉任意一个，不影响整个集群对外提供服务。
伸缩性，服务端支持随意增加节点。订阅者可以感知服务端节点的变动，但是发布者并不能自动感知。

3个node的集群

$ gnatsd -p 4222 -m 4333 -cluster nats://localhost:4248 -routes nats://localhost:5248,nats://localhost:6248 -DV  
$ gnatsd -p 5222 -m 5333 -cluster nats://localhost:5248 -routes nats://localhost:4248,nats://localhost:6248 -DV 
$ gnatsd -p 6222 -m 6333 -cluster nats://localhost:6248 -routes nats://localhost:4248,nats://localhost:5248 -DV 

-p 端口：服务端口，发布者，订阅者需要使用此端口。
-m 端口: 监控端口。
-cluster 地址:作为集群节点对其他节点提供服务的地址，其他节点需要连接的地址。(其他节点的-routes 可以填写此地址)
-routes 地址：此节点，路由到其他地址的列表(也就是其他节点的-cluster)
-DV Debug and trace

gnatsd -p 服务提供端口 -m 服务监控端口 -cluster 集群内node地址 -routes 集群内其他node地址列表 -DV

Server

package main

import (
    "github.com/nats-io/go-nats"
    "log"
    "flag"
    "fmt"
    "time"
)

const (
    //url   = "nats://192.168.3.125:4222"
    //url = nats.DefaultURL
    url = "nats://localhost:4222,nats://localhost:6222"
    //url = "nats://localhost:4222,nats://localhost:5222,nats://localhost:6222"
)

var (
    nc  *nats.Conn
    err error
)

func init() {

    if nc, err = nats.Connect(url, nats.DontRandomize(), nats.MaxReconnects(5), nats.ReconnectWait(2*time.Second), nats.DisconnectHandler(func(nc *nats.Conn) {
        fmt.Printf("Got disconnected!\n")
    }),
        nats.ReconnectHandler(func(_ *nats.Conn) {
            fmt.Printf("Got reconnected to %v!\n", nc.ConnectedUrl())
        }),
        nats.ClosedHandler(func(nc *nats.Conn) {
            fmt.Printf("Connection closed. Reason: %q\n", nc.LastError())
        }), nats.DiscoveredServersHandler(func(conn *nats.Conn) {
            fmt.Printf("Got Discover Server %v!\n", nc.ConnectedUrl())
        }), nats.ErrorHandler(func(conn *nats.Conn, subscription *nats.Subscription, e error) {
            fmt.Printf("Got Error Server %v!\n",e)
        })); checkErr(err) {
        //

    }
}

func main() {
    var (
        servername = flag.String("servername", "y", "name for server")
        queueGroup = flag.String("group", "", "group name for Subscribe")
        subj       = flag.String("subj", "abc", "subject name")
    )
    flag.Parse()

    log.Println(*servername, *queueGroup, *subj)
    startService(*subj, *servername+" worker1", *queueGroup)
    //startService(*subj, *servername+" worker2", *queueGroup)
    //startService(*subj, *servername+" worker3", *queueGroup)

    select {}
}

//receive message
func startService(subj, name, queue string) {
    go async(nc, subj, name, queue)
}

func async(nc *nats.Conn, subj, name, queue string) {
    _, e := nc.QueueSubscribe(subj, queue, func(msg *nats.Msg) {
        log.Println(name, "Received a message From Async : ", string(msg.Data))
    })

    checkErr(e)
}

func checkErr(err error) bool {
    if err != nil {
        log.Println("error:", err)
        return false
    }
    return true
}

Client

package main

import (
    "github.com/nats-io/go-nats"
    "log"
    "strconv"
    "github.com/pborman/uuid"
    "flag"
    "time"
    "fmt"
)

const (
    //url   = "nats://192.168.3.125:4222"
    //url = "nats://localhost:4222"
    //url = "nats://localhost:4222,nats://localhost:6222"
    url = "nats://localhost:4222,nats://localhost:5222,nats://localhost:6222"
    //url = "nats://localhost:5222"
)

var (
    nc  *nats.Conn
    err error
)

func init() {
    if nc, err = nats.Connect(url, nats.DontRandomize(), nats.MaxReconnects(10), nats.ReconnectWait(2*time.Second), nats.DisconnectHandler(func(nc *nats.Conn) {
        fmt.Printf("Got disconnected!\n")
    }),
        nats.ReconnectHandler(func(_ *nats.Conn) {
            fmt.Printf("Got reconnected to %v!\n", nc.ConnectedUrl())
        }),
        nats.ClosedHandler(func(nc *nats.Conn) {
            fmt.Printf("Connection closed. Reason: %q\n", nc.LastError())
        })); checkErr(err) {
        //
    }
    nc.SetDiscoveredServersHandler(func(conn *nats.Conn) {
        
    })
}

func main() {
    var (
        subj = flag.String("subj", "abc", "subject name")
    )
    flag.Parse()
    log.Println(*subj)
    startClient(*subj)

    time.Sleep(time.Second)
}

//send message to server
func startClient(subj string) {
    for i := 0; i < 1; i++ {
        id := uuid.New()
        log.Println(id)
        nc.Publish(subj, []byte(id+" Golang "+strconv.Itoa(i)))
        //nc.Publish(subj, []byte(id+" Rain "+strconv.Itoa(i)))
        //nc.Publish(subj, []byte(id+" Fog "+strconv.Itoa(i)))
        //nc.Publish(subj, []byte(id+" Cloudy "+strconv.Itoa(i)))
    }
}

func checkErr(err error) bool {
    if err != nil {
        log.Println(err)
        return false
    }
    return true
}

注意

• 发布者和订阅者都需要指明3个节点的ur地址
  nats://localhost:4222,nats://localhost:5222,nats://localhost:6222
• 如果3个node都不可用，发布者会发送消息失败。
• 如果3个node至少有一个可用，订阅者就会收到消息。
• 如果3个node全都不可用，订阅者会自动断开连接。
• 增加一个node nats://localhost:7222,订阅者可以自动连接。
• 增加node后，3个node全都不可用，订阅者不会断开连接，可以接受从新node发布的消息。
• 3个node恢复后，订阅者可以接受3个node的消息。

后续

发布者和订阅者

• 原始集群中node都不可用
• 主动查询可用node
• 接受可用node通知
• 向可用node发送消息，订阅可用node的消息
• 以上内容需要配合服务发现中间件或者自己实现

配置文件启动

$ gnatsd -c nodea.cfg
$ gnatsd -c nodeb.cfg
$ gnatsd -c nodec.cfg

nodea.cfg

listen: localhost:4222 # host/port to listen for client connections

http: localhost:4333 # HTTP monitoring port

# Authorization for client connections
#authorization {
  #user:     yasenagat
  # ./util/mkpasswd -p T0pS3cr3t
  #password: $2a$11$W2zko751KUvVy59mUTWmpOdWjpEm5qhcCZRd05GjI/sSOT.xtiHyG
  #ytc
  #token:   $2a$11$ZuYXelbdaRQnOcADEx40yOtinCvEi9c3X64K2Kyx7wLJq7ECPUnA2
  #timeout:  1
#}

# Cluster definition

cluster {

  listen: localhost:4248 # host/port for inbound route connections

  # Authorization for route connections
  #authorization {
    #user: user2
    # ./util/mkpasswd -p T0pS3cr3tT00!
    #password: $2a$11$xH8dkGrty1cBNtZjhPeWJewu/YPbSU.rXJWmS6SFilOBXzmZoMk9m
    #yctc
    #token: $2a$11$d/RrRseSiPOd/fxurspFquSirrjseRFRFGHdRbte7D8wj2laCLcVS
    #timeout: 0.5
  #}

  # Routes are actively solicited and connected to from this server.
  # Other servers can connect to us if they supply the correct credentials
  # in their routes definitions from above.

  routes = [
    nats-route://127.0.0.1:5248
    nats-route://127.0.0.1:6248
  ]
}

# logging options
debug:   false
trace:   true
logtime: false
log_file: "nodea.log"

# pid file
pid_file: "nodea.pid"

# Some system overides

# max_connections
max_connections: 100

# max_subscriptions (per connection)
max_subscriptions: 1000

# maximum protocol control line
max_control_line: 512

# maximum payload
max_payload: 65536

# Duration the server can block on a socket write to a client.  Exceeding the
# deadline will designate a client as a slow consumer.
write_deadline: "2s"

nodeb.cfg

listen: localhost:5222 # host/port to listen for client connections

http: localhost:5333 # HTTP monitoring port

# Authorization for client connections
authorization {
  #user:     yasenagat
  # ./util/mkpasswd -p T0pS3cr3t
  #password: $2a$11$W2zko751KUvVy59mUTWmpOdWjpEm5qhcCZRd05GjI/sSOT.xtiHyG
  #ytb
  token:   $2a$11$ToARKoxzTSTXxKCljOFe4eDmiPQ/EcaB0M7V8mGE1tfgOv97.iECe
  timeout:  1
}

# Cluster definition

cluster {

  listen: localhost:5248 # host/port for inbound route connections

  # Authorization for route connections
  authorization {
    #user: user1
    # ./util/mkpasswd -p T0pS3cr3tT00!
    #password: pass1
    #yctb
    token: $2a$11$EriHSUV8WO7PWUXTxOCY5uP7MhAswLE2tqQQPuz6kaoF89KhO8CcW
    timeout: 0.5
  }

  # Routes are actively solicited and connected to from this server.
  # Other servers can connect to us if they supply the correct credentials
  # in their routes definitions from above.

  routes = [
    nats-route://127.0.0.1:4248
    nats-route://127.0.0.1:6248
  ]
}

# logging options
debug:   false
trace:   true
logtime: false
log_file: "nodeb.log"

# pid file
pid_file: "nodeb.pid"

# Some system overides

# max_connections
max_connections: 100

# max_subscriptions (per connection)
max_subscriptions: 1000

# maximum protocol control line
max_control_line: 512

# maximum payload
max_payload: 65536

# Duration the server can block on a socket write to a client.  Exceeding the
# deadline will designate a client as a slow consumer.
write_deadline: "2s"

nodec.cfg

listen: localhost:6222 # host/port to listen for client connections

http: localhost:6333 # HTTP monitoring port

# Authorization for client connections
#authorization {
  #user:     yasenagat
  # ./util/mkpasswd -p T0pS3cr3t
  #password: $2a$11$W2zko751KUvVy59mUTWmpOdWjpEm5qhcCZRd05GjI/sSOT.xtiHyG
  #ytc
  #token:   $2a$11$HZy0M3lcxxzJRsFhtAoiX.jCuqKLyztcYYZPWRtlR.APhs/4mFYGC
  #timeout:  1
#}

# Cluster definition

cluster {

  listen: localhost:6248 # host/port for inbound route connections

  # Authorization for route connections
  #authorization {
    #user: user2
    # ./util/mkpasswd -p T0pS3cr3tT00!
    #password: $2a$11$xH8dkGrty1cBNtZjhPeWJewu/YPbSU.rXJWmS6SFilOBXzmZoMk9m
    #yctc
    #token: $2a$11$srwaIbFHGwIt37t3GrPynOHSpZ2LHTtw1QXWuznXGOaknEwulP4o6
    #timeout: 0.5
  #}

  # Routes are actively solicited and connected to from this server.
  # Other servers can connect to us if they supply the correct credentials
  # in their routes definitions from above.

  routes = [
    nats-route://127.0.0.1:5248
    nats-route://127.0.0.1:4248
  ]
}

# logging options
debug:   false
trace:   true
logtime: false
log_file: "nodec.log"

# pid file
pid_file: "nodec.pid"

# Some system overides

# max_connections
max_connections: 100

# max_subscriptions (per connection)
max_subscriptions: 1000

# maximum protocol control line
max_control_line: 512

# maximum payload
max_payload: 65536

# Duration the server can block on a socket write to a client.  Exceeding the
# deadline will designate a client as a slow consumer.
write_deadline: "2s"