如何在erlang应用程序中启动多个webmachine实例？

Question

我试图在一个erlang应用程序中创建两个webmachine实例。每个实例都要在不同的端口上运行，并有自己的特定配置。在webmachine 这里之后，我添加了以下要在主管规范(application_sup.erl)中启动的进程：

 {
    webmachine_instance_1,
    { webmachine_mochiweb, start, 
       [
          [
              { ip, "0.0.0.0"},
              { port, 8000},
              { dispatch, [ {["*"], file_resource, []} ] }
          ] 
        ]
    },
    permanent,
    5000,
    worker,
    dynamic
 },
 {
    webmachine_instance_2,
    { webmachine_mochiweb, start, 
       [
          [
              { ip, "0.0.0.0"},
              { port, 8080},
              { dispatch, [ {["*"], file_resource, []} ] }
          ] 
       ]
    },
    permanent,
    5000,
    worker,
    dynamic
 }

当我包含这两个实例时，我会得到一个启动错误，无法启动我的erlang应用程序。在尝试使用webmachine的单个实例(webmachine_instance_1或webmachine_instance_2)运行应用程序之后，我的应用程序启动良好。

以下是具体的错误：

=PROGRESS REPORT==== 11-Mar-2014::17:00:31 ===
      supervisor: {local, application_sup}
         started: [{pid,<0.230.0>},
                   {name,webmachine_instance_1},
                   {mfargs,
                       {webmachine_mochiweb,start,
                           [[{ip,"0.0.0.0"},
                             {port,8000},
                             {dispatch, [{['*'],
                                   file_resource,
                                   []
                             }]}]
                            ]
                        }
                   },
                   {restart_type,permanent},
                   {shutdown,5000},
                   {child_type,worker}] 

 =SUPERVISOR REPORT==== 11-Mar-2014::17:00:31 ===
     Supervisor: {local, application_sup}
     Context:    start_error
     Reason:     {'EXIT',
                 {undef,
                     [{webmachine_mochiweb,start,
                          [{ip,"0.0.0.0"},
                           {port,8080},
                           {dispatch,[{["*"],file_resource,[]}]}],
                          []},
                      {supervisor,do_start_child,2,
                          [{file,"supervisor.erl"},{line,303}]},
                      {supervisor,start_children,3,
                          [{file,"supervisor.erl"},{line,287}]},
                      {supervisor,init_children,2,
                          [{file,"supervisor.erl"},{line,253}]},
                      {gen_server,init_it,6,
                          [{file,"gen_server.erl"},{line,304}]},
                      {proc_lib,init_p_do_apply,3,
                          [{file,"proc_lib.erl"},{line,227}]}]}}
 Offender:   [{pid,undefined},
              {name,webmachine_instance_2},
              {mfargs,
                  {webmachine_mochiweb,start,
                      [{ip,"0.0.0.0"},
                       {port,8080},
                       {dispatch,[{["*"],file_resource,[]}]}]}},
              {restart_type,permanent},
              {shutdown,5000},
              {child_type,worker}]

我对erlang相当陌生，可能不太了解这里的基本问题--根据webmachine文档，我们应该能够启动相同应用程序的两个实例，但在erlang应用程序中有不同的配置。

谢谢你对这个问题的任何帮助/讨论！

Answer 1

您的子进程配置应该具有以下形式：

{Name,
 {webmachine_mochiweb, start, [WebConfig]},
  permanent, 5000, worker, [mochiweb_socket_server]}

其中，Name和WebConfig必须是您的and机器实例所特有的。WebConfig部件应该包括name和dispatch_group属性。例如：

WebConfig = [{name,instance1},
             {dispatch_group,instance1},
             {ip, Ip},
             {port, Port},
             {log_dir, "priv/log"},
             {dispatch, Dispatch}],

因此，对于多个实例，您可能有类似于主管规范的如下内容：

WebConfig1 = [{name,instance1},
              {dispatch_group,instance1},
              {ip, Ip},
              {port, Port},
              {log_dir, "priv/log"},
              {dispatch, Dispatch}],
WebConfig2 = [{name,instance2},
              {dispatch_group,instance2},
              {ip, Ip},
              {port, Port+1},
              {log_dir, "priv/log"},
              {dispatch, Dispatch}],
Web1 = {instance1,
        {webmachine_mochiweb, start, [WebConfig1]},
        permanent, 5000, worker, [mochiweb_socket_server]},
Web2 = {instance2,
        {webmachine_mochiweb, start, [WebConfig2]},
        permanent, 5000, worker, [mochiweb_socket_server]},
Processes = [Web1, Web2],
{ok, { {one_for_one, 10, 10}, Processes} }.

另一件事:从问题中出现的名称application_sup判断，您可能已经运行了webmachine ./scripts/new_webmachine.sh，并将应用程序名指定为application。如果是这样，请不要这样做，因为application是一个关键的Erlang模块的名称，您的代码将与它发生冲突并导致各种问题。