go微服务系列之二

这是使用gomicro开发微服务系列的第二篇，在上一篇中我只是使用了user-srv和web-srv实现了一个demo，在这里我将实用consul实现服务发现。如果想直接查阅源码或者通过demo学习的，可以访问ricoder_demo。

如何编写一个微服务？这里用的是go的微服务框架go micro，具体的情况可以查阅：http://btfak.com/%E5%BE%AE%E6%9C%8D%E5%8A%A1/2016/03/28/go-micro/

一、如何安装consul

我的开发系统采用的是ubunt16.04，这里就给出ubuntu下安装consul的步骤：

$ wget https://releases.hashicorp.com/consul/0.7.2/consul_0.7.2_linux_amd64.zip
$ sudo apt-get install unzip

$ ls

$ unzip consul_0.7.2_linux_amd64.zip
$ sudo mv consul /usr/local/bin/consul

$ wget https://releases.hashicorp.com/consul/0.7.2/consul_0.7.2_web_ui.zip
$ unzip consul_0.7.2_web_ui.zip
$ mkdir -p /usr/share/consul
$ mv dist /usr/share/consul/ui

Consul 压缩包地址：https://www.consul.io/downloads.html

验证安装是否成功的方法：

$ consul
Usage: consul [--version] [--help]  []

Available commands are:
    agent          Runs a Consul agent
    catalog        Interact with the catalog
    event          Fire a new event
    exec           Executes a command on Consul nodes
    force-leave    Forces a member of the cluster to enter the "left" state
    info           Provides debugging information for operators.
    join           Tell Consul agent to join cluster
    keygen         Generates a new encryption key
    keyring        Manages gossip layer encryption keys
    kv             Interact with the key-value store
    leave          Gracefully leaves the Consul cluster and shuts down
    lock           Execute a command holding a lock
    maint          Controls node or service maintenance mode
    members        Lists the members of a Consul cluster
    monitor        Stream logs from a Consul agent
    operator       Provides cluster-level tools for Consul operators
    reload         Triggers the agent to reload configuration files
    rtt            Estimates network round trip time between nodes
    snapshot       Saves, restores and inspects snapshots of Consul server state
    validate       Validate config files/directories
    version        Prints the Consul version
    watch          Watch for changes in Consul

启动consul服务的方法：

$ consul agent -dev
==> Starting Consul agent...
==> Consul agent running!
           Version: 'v0.9.3'
           Node ID: '199ee0e9-db61-f789-b22a-b6b472f63fbe'
         Node name: 'ricoder'
        Datacenter: 'dc1' (Segment: '')
            Server: true (Bootstrap: false)
       Client Addr: 127.0.0.1 (HTTP: 8500, HTTPS: -1, DNS: 8600)
      Cluster Addr: 127.0.0.1 (LAN: 8301, WAN: 8302)

优雅的停止服务的方法：

命令：CTRL+C

其他命令：

consul members：查看集群成员
consul info：查看当前服务器的状况
consul leave：退出当前服务集群

成功开启consul服务后可以登录后台访问地址：http://localhost:8500，如下：

Screenshot from 2017-10-14 13-35-58.png

二、api-srv的开发，实现动态路由

根据官方对api-srv的介绍：The micro api is an API gateway for microservices. Use the API gateway pattern to provide a single entry point for your services. The micro api serves HTTP and dynamically routes to the appropriate backend service.
粗略翻译的意思就是：api-srv是微服务的网关，使用API网关模式可以为我们的服务提供一个入口，api-srv提供HTTP服务，并动态路由到相应的后端服务。

步骤1：监听8082端口，并绑定handler处理http请求

    mux := http.NewServeMux()
    mux.HandleFunc("/", handleRPC)
    log.Println("Listen on :8082")
    http.ListenAndServe(":8082", mux)

步骤2：实现handler，并实现跨域处理

    if r.URL.Path == "/" {
        w.Write([]byte("ok,this is the server ..."))
        return
    }

    // 跨域处理
    if origin := r.Header.Get("Origin"); cors[origin] {
        w.Header().Set("Access-Control-Allow-Origin", origin)
    } else if len(origin) > 0 && cors["*"] {
        w.Header().Set("Access-Control-Allow-Origin", origin)
    }

    w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS")
    w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Content-Length, Accept-Encoding, X-Token, X-Client")
    w.Header().Set("Access-Control-Allow-Credentials", "true")
    if r.Method == "OPTIONS" {
        return
    }

    if r.Method != "POST" {
        http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
        return
    }

步骤3：实现将url转换为service和method，这里我采用了pathToReceiver这个函数来处理

    p = path.Clean(p)
    p = strings.TrimPrefix(p, "/")
    parts := strings.Split(p, "/")

    // If we've got two or less parts
    // Use first part as service
    // Use all parts as method
    if len(parts) <= 2 {
        service := ns + strings.Join(parts[:len(parts)-1], ".")
        method := strings.Title(strings.Join(parts, "."))
        return service, method
    }

    // Treat /v[0-9]+ as versioning where we have 3 parts
    // /v1/foo/bar => service: v1.foo method: Foo.bar
    if len(parts) == 3 && versionRe.Match([]byte(parts[0])) {
        service := ns + strings.Join(parts[:len(parts)-1], ".")
        method := strings.Title(strings.Join(parts[len(parts)-2:], "."))
        return service, method
    }

    // Service is everything minus last two parts
    // Method is the last two parts
    service := ns + strings.Join(parts[:len(parts)-2], ".")
    method := strings.Title(strings.Join(parts[len(parts)-2:], "."))
    return service, method

http传进来的url是http://127.0.0.1:8082/user/userService/SelectUser，我在handler中通过以下方式调用后：

service, method := apid.PathToReceiver(config.Namespace, r.URL.Path)

service和method分别是：

2017/10/14 13:56:12 service:com.class.cinema.user
2017/10/14 13:56:12 method:UserService.SelectUser

注意：var config.Namespace = "com.class.cinema"

步骤4：封装request，调用服务

    br, _ := ioutil.ReadAll(r.Body)

    request := json.RawMessage(br)

    var response json.RawMessage
    req := (*cmd.DefaultOptions().Client).NewJsonRequest(service, method, &request)
    ctx := apid.RequestToContext(r)
    err := (*cmd.DefaultOptions().Client).Call(ctx, req, &response)

在这里Call就是调用相应服务的关键。

步骤5：对err进行相应的处理和返回调用结果

// make the call
    if err != nil {
        ce := microErrors.Parse(err.Error())
        switch ce.Code {
        case 0:
            // assuming it's totally screwed
            ce.Code = 500
            ce.Id = service
            ce.Status = http.StatusText(500)
            // ce.Detail = "error during request: " + ce.Detail
            w.WriteHeader(500)
        default:
            w.WriteHeader(int(ce.Code))
        }
        w.Write([]byte(ce.Error()))
        return
    }
    b, _ := response.MarshalJSON()
    w.Header().Set("Content-Length", strconv.Itoa(len(b)))
    w.Write(b)

通过对err的处理，在请求的method或者service不存在时，如：