“服务器"到“服务器"零MQ通信 [英] "Server" to "Server" ZeroMQ communication

问题描述

我想构建一个具有以下架构的系统:

I want to build a system that has the following architecture:

+------------------+          +------------------+
| App1. 0mq client | <------> | App2. 0mq server |
+------------------+          +------------------+

其中
App2 是一个 ZeroMQ 服务器，它是一个黑匣子，
和
App1 是一个 ZeroMQ 客户端，但它实际上是一个前端服务器.前端服务器将处理来自客户端的一些请求，然后与 App2 服务器进行通信.

where
App2 is a ZeroMQ server and it's a black box,
and
App1 is a ZeroMQ client, but it is in fact a frontend server. The frontend server will process some requests from the clients and then will communicate with the App2 server.

鉴于:

1. 在任何时候，任何服务器"都可能关闭或重新启动.
2. 我想启动任何应用，即使其他应用没有运行.
3. 如果 App1 在 App2 关闭时启动，我想知道 App2 何时启动.

1. At any point in time any of the "servers" can go down or be restarted.
2. I want to start any of the apps, even if the other app is not running.
3. If App1 is started when App2 is down, I want to know when App2 is up.

是否可以仅使用 ZeroMQ 内置函数 来实现 3.，或者我是否需要使用不同的机制来通知 App1 App2 上线?

推荐答案

Item 3: using pure ZeroMQ built-ins

Fig.1: 为什么使用简单的REQ/REP

Item 3: using pure ZeroMQ built-ins

Fig.1: Why it is wrong to use a naive REQ/REP

               XTRN_RISK_OF_FSA_DEADLOCKED ~ {  NETWORK_LoS
                                         :   || NETWORK_LoM
                                         :   || SIG_KILL( App2 )
                                         :   || ...
                                         :      }
                                         :
[App1]      ![ZeroMQ]                    :    [ZeroMQ]              ![App2] 
code-control! code-control               :    [code-control         ! code-control
+===========!=======================+    :    +=====================!===========+
|           ! ZMQ                   |    :    |              ZMQ    !           |
|           ! REQ-FSA               |    :    |              REP-FSA!           |
|           !+------+BUF> .connect()|    v    |.bind()  +BUF>------+!           |
|           !|W2S   |___|>tcp:>---------[*]-----(tcp:)--|___|W2R   |!           |
|     .send()>-o--->|___|           |         |         |___|-o---->.recv()     |
| ___/      !| ^  | |___|           |         |         |___| ^  | |!      \___ |
| REQ       !| |  v |___|           |         |         |___| |  v |!       REP |
| \___.recv()<----o-|___|           |         |         |___|<---o-<.send()___/ |
|           !|   W2R|___|           |         |         |___|   W2S|!           |
|           !+------<BUF+           |         |         <BUF+------+!           |
|           !                       |         |                     !           |
|           ! ZMQ                   |         |   ZMQ               !           |
|           ! REQ-FSA               |         |   REP-FSA           !           |
~~~~~~~~~~~~~ DEADLOCKED in W2R ~~~~~~~~ * ~~~~~~ DEADLOCKED in W2R ~~~~~~~~~~~~~
|           ! /\/\/\/\/\/\/\/\/\/\/\|         |/\/\/\/\/\/\/\/\/\/\/!           |
|           ! \/\/\/\/\/\/\/\/\/\/\/|         |\/\/\/\/\/\/\/\/\/\/\!           |
+===========!=======================+         +=====================!===========+

<小时>

Fig.2: 如何实现需求Item 3，使用纯ZeroMQ代码> 内置函数.

App1.PULL.recv( ZMQ.NOBLOCK ) 和 App1.PULL.poll( 0 )很明显

App1.PULL.recv( ZMQ.NOBLOCK ) and App1.PULL.poll( 0 ) are obvious

[App1]      ![ZeroMQ]
code-control! code-control           
+===========!=======================+
|           !                       |
|           !+----------+           |         
|     .poll()|   W2R ___|.bind()    |         
| ____.recv()<----o-|___|-(tcp:)--------O     
| PULL      !|      |___|           |   :   
|           !|      |___|           |   :   
|           !|      |___|           |   :   
|           !+------<BUF+           |   :     
|           !                       |   :                           ![App2]
|           !                       |   :     [ZeroMQ]              ! code-control
|           !                       |   :     [code-control         ! once gets started ...
|           !                       |   :     +=====================!===========+
|           !                       |   :     |                     !           |
|           !                       |   :     |         +----------+!           |
|           !                       |   :     |         |___       |!           |
|           !                       |   :     |         |___| <--o-<.send()____ |
|           !                       |   :<<-------<tcp:<|___|   W2S|!      PUSH |
|           !                       |   :    .connect() <BUF+------+!           |
|           !                       |   :     |                     !           |
|           !                       |   :     |                     !           |
+===========!=======================+   :     +=====================!===========+

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