之前发过一篇帖子应用.Net+Consul维护RabbitMq的高可用性，然后最近老大问我当初我这么搞是抽的什么想法- -然后顺便贴了两行C#代码：
var factory = new ConnectionFactory()
{
UserName = "username",
Password = "password",
AutomaticRecoveryEnabled = true,
TopologyRecoveryEnabled = true
};
Connection = factory.CreateConnection(new string[] { "ip1", "ip2", "ip3" });
AutomaticRecoveryEnabled的作用就是断线重连，假如当前的连接断开了，连接不会释放
TopologyRecoveryEnabled 重连后恢复当前的工作进程，比如channel、queue、发布的消息进度等。
看上去其实却是比较方便的，为了狡辩我当场列出了我设计的方案的主要优点:
1.rabbitmq网关设计的时候一方面是为了让客户端能够保证建立与master节点的连接，直连master性能较高。
2.通过配置队列名+VirthHost可以获取队列信息，Consul可以起到配置中心的作用，可配置性高一些(其实此处是狡辩。。)
3.RabbitMQ与Master队列建立的连接在发生故障时会第一时间查询网关获取新的Mater队列信息进行重连（当然代码内部也有重试机制，不会随便就更换连接的），相比于AutomaticRecoveryEnabled效率更高一些。
4.客户端SDK内部实现定时更新队列连接，发现Master节点更换时重新建立连接
看上去我设计的方案还是有点意义的（其实是真懒得改代码）
不过此处有个问题就是既然创建连接时的参数可以提供多个IP的集合，假如RabbitMQ提供的客户端SDK内部实现的更好，那我狡辩什么不也完戏了吗。。。于是假装下载了下客户端sdk代码扫了扫，此处以C#代码为例，代码还是比较简单的。github地址
直接定位ConnectionFactory类找CreateConnection()方法
/// <summary>
/// Create a connection using a list of hostnames using the configured port.
/// By default each hostname is tried in a random order until a successful connection is
/// found or the list is exhausted using the DefaultEndpointResolver.
/// The selection behaviour can be overriden by configuring the EndpointResolverFactory.
/// </summary>
/// <param name="hostnames">
/// List of hostnames to use for the initial
/// connection and recovery.
/// </param>
/// <returns>Open connection</returns>
/// <exception cref="BrokerUnreachableException">
/// When no hostname was reachable.
/// </exception>
public IConnection CreateConnection(IList<string> hostnames)
{
return CreateConnection(hostnames, null);
} /// <summary>
/// Create a connection using a list of hostnames using the configured port.
/// By default each endpoint is tried in a random order until a successful connection is
/// found or the list is exhausted.
/// The selection behaviour can be overriden by configuring the EndpointResolverFactory.
/// </summary>
/// <param name="hostnames">
/// List of hostnames to use for the initial
/// connection and recovery.
/// </param>
/// <param name="clientProvidedName">
/// Application-specific connection name, will be displayed in the management UI
/// if RabbitMQ server supports it. This value doesn't have to be unique and cannot
/// be used as a connection identifier, e.g. in HTTP API requests.
/// This value is supposed to be human-readable.
/// </param>
/// <returns>Open connection</returns>
/// <exception cref="BrokerUnreachableException">
/// When no hostname was reachable.
/// </exception>
public IConnection CreateConnection(IList<string> hostnames, String clientProvidedName)
{
var endpoints = hostnames.Select(h => new AmqpTcpEndpoint(h, this.Port, this.Ssl));
return CreateConnection(new DefaultEndpointResolver(endpoints), clientProvidedName);
} /// <summary>
/// Create a connection using a list of endpoints. By default each endpoint will be tried
/// in a random order until a successful connection is found or the list is exhausted.
/// The selection behaviour can be overriden by configuring the EndpointResolverFactory.
/// </summary>
/// <param name="endpoints">
/// List of endpoints to use for the initial
/// connection and recovery.
/// </param>
/// <returns>Open connection</returns>
/// <exception cref="BrokerUnreachableException">
/// When no hostname was reachable.
/// </exception>
public IConnection CreateConnection(IList<AmqpTcpEndpoint> endpoints)
{
return CreateConnection(new DefaultEndpointResolver(endpoints), null);
} /// <summary>
/// Create a connection using an IEndpointResolver.
/// </summary>
/// <param name="endpointResolver">
/// The endpointResolver that returns the endpoints to use for the connection attempt.
/// </param>
/// <param name="clientProvidedName">
/// Application-specific connection name, will be displayed in the management UI
/// if RabbitMQ server supports it. This value doesn't have to be unique and cannot
/// be used as a connection identifier, e.g. in HTTP API requests.
/// This value is supposed to be human-readable.
/// </param>
/// <returns>Open connection</returns>
/// <exception cref="BrokerUnreachableException">
/// When no hostname was reachable.
/// </exception>
public IConnection CreateConnection(IEndpointResolver endpointResolver, String clientProvidedName)
{
IConnection conn;
try
{
if (AutomaticRecoveryEnabled)
{
var autorecoveringConnection = new AutorecoveringConnection(this, clientProvidedName);
autorecoveringConnection.Init(endpointResolver);
conn = autorecoveringConnection;
}
else
{
IProtocol protocol = Protocols.DefaultProtocol;
conn = protocol.CreateConnection(this, false, endpointResolver.SelectOne(this.CreateFrameHandler), clientProvidedName);
}
}
catch (Exception e)
{
throw new BrokerUnreachableException(e);
} return conn;
}
代码比较直观，第二个方法的时候把传入的字符串集合转换成了AmqpTcpEndpoint集合，AmqpTcpEndpoint里包含队列绑定信息，包含默认ip,端口,SSL配置信息，RabbitMQ的Amqp协议信息，初始化Socket连接的协议类型（一个AddressFamily枚举），当然都是可配置的（除了ip貌似都喜欢使用默认的）。
然后就倒主要部分了。
if (AutomaticRecoveryEnabled)
{
var autorecoveringConnection = new AutorecoveringConnection(this, clientProvidedName);
autorecoveringConnection.Init(endpointResolver);
conn = autorecoveringConnection;
}
else
{
IProtocol protocol = Protocols.DefaultProtocol;
conn = protocol.CreateConnection(this, false, endpointResolver.SelectOne(this.CreateFrameHandler), clientProvidedName);
}
由于主要想看看传入多个连接是不是可以智能的选择master连接，所以此处直接看else里的代码就行了。。。（其实一样。。）
protocol.CreateConnection方法调用时传入的第三个参数endpointResolver.SelectOne(this.CreateFrameHandler)作用其实就是选择连接然后扔到CreateFrameHandler委托里作为参数进行Socket初始化的。看一下SelectOne这个扩展方法即可。。看了两行终于可以继续狡辩了。。
public static T SelectOne<T>(this IEndpointResolver resolver, Func<AmqpTcpEndpoint, T> selector)
{
var t = default(T);
Exception exception = null;
foreach(var ep in resolver.All())
{
try
{
t = selector(ep);
if(t.Equals(default(T)) == false)
{
return t;
}
}
catch (Exception e)
{
exception = e;
}
} if(Object.Equals(t, default(T)) && exception != null)
{
throw exception;
} return t;
}
这个foreach还是“比较好的”，能够建立一个Socket连接就愉快的返回了!，不过这个resolver.All()里是不是还有玄机呢！看了一眼。。终于放心了。。
public class DefaultEndpointResolver : IEndpointResolver
{
private List<AmqpTcpEndpoint> endpoints;
private Random rnd = new Random(); public DefaultEndpointResolver (IEnumerable<AmqpTcpEndpoint> tcpEndpoints)
{
this.endpoints = tcpEndpoints.ToList();
} public IEnumerable<AmqpTcpEndpoint> All()
{
return endpoints.OrderBy(item => rnd.Next());
}
就是随机排序一下。。不过这么看自己实现下IEndpointResolver接口改个选择master队列的策略也是不错的。