RabbitMQ. Part 2. Understanding Exchanges

Exchange- exchanger or exchange point. Messages are sent to it. Exchange Distributes the message into one or more queues. It routes messages to the queue based on the created connections ( bindings) between it and the queue.

Exchangenot an Erlang process . For scalability reasons exchange, this is a string (a link to a module with code where the routing logic lies) in the mnesia built-in database . 1 thousand exchangers will consume only 1MB of memory.

Table of contents

• RabbitMQ. Part 1. Introduction. Erlang, AMQP and RPC
• RabbitMQ. Part 2. Understanding Exchanges
• RabbitMQ. Part 3. Understanding Queues and Bindings
• RabbitMQ. Part 4. Details about Connection and Chanel
• RabbitMQ. Part 5. Understanding what messages and frames are
• RabbitMQ. Part 6. Message publishing and consumption performance
• RabbitMQ. Part 7. Overview of Federation and Shovel modules
• RabbitMQ. Part 8. RabbitMQ in .NET
• RabbitMQ. Part 9. Monitoring

Direct exchange

Direct exchange — , . , . — . .

:

rabbitmq . direct exchange . , .

Topic Exchange

Topic exchange – direct exchange . , , . 0 ( AZ az 0-9), , * #.

• * — 1
• # — 0

:

RabbitMQ 2.4.0 topic exchange 145 . trie implementation, . a.b.c, a.*.b.c, a.#.c b.b.c :

, .

:

• , .. , direct exchange fanout exchange
• , * , , #.
• topic exchange direct exchange

Fanout Exchange

Fanout exchange – .

:

• RabbitMQ . exchange;
• ;

:

Headers Exchange

Headers exchange — (, ) headers . headers Dictionary<, >.

x-match any, (, ). or.

var bindingArguments = new Dictinary<String, Object>();
bindingArguments.add("x-match", "any");

x-match all. , (, ). and.

:

:

• . (, ) headers . , exchange.

Consistent-Hashing Exchange

RabbitMQ.

Consistent-hashing exchange (exchange ) – , , , . ( 0 - n).

– , ( ). .

:

Hash headers . headers, . headers.

, , .

(E2E)

Exchange-to-Exchange ( AMQP. RabbitMQ).

:

E2E , , .

Exchange

RPC . Exchange.Declare, :

exchange RabbitMQ.Client:

//...
channel.ExchangeDeclare(
    exchange: "my_exchange",
    type: "direct",
    durable: "false",
    autoDelete: "false",
    arguments: null
);
//...

• exchange — , .
• type —
• durable — true, exchange . /. false, exchange , /
• autoDelete — . Exchange ,
• arguments — . , alternative exchange ( ). , .

exchange , RPC Exchange.DeclareOk. ( Exchange.Declare), Channel.Close OperationInterruptedException, .

. - — RabbitMQ .

Exchange

RabbitMQ guest (username: guest password: guest). , guest . Exchanges Add a new exchange. :

. , Internal, E2E. Producer .

. , .. (). . .

, , fanout exchange, 1:1 . , fanout exchange .

, topic exchange , , direct exchnge, .. topic exchange.

exchange , , .

exchange .

Queues Bindings.

Code

C#, . .

public interface IExchange
{
    /// <summary>
    ///      ,    . 
    ///        .
    /// </summary>
    string Name { get; }

    /// <summary>
    ///      
    /// </summary>
    string Type { get; }

    /// <summary>
    ///       true,  exchange  
    ///      . 
    ///            
    ///       /. 
    ///       false,  exchange  
    ///        , 
    ///      /  
    /// </summary>
    bool IsDurable { get; }

    /// <summary>
    ///      . Exchange  , 
    ///            
    /// </summary>
    bool IsAutoDelete { get; }

    /// <summary>
    ///      
    /// </summary>
    IDictionary<string, object> Arguments { get; }
}

/// <summary>
///      
/// </summary>
public static class ExchangeType
{
    public const string Direct = "direct";
    public const string Topic = "topic";
    public const string Fanout = "fanout";
    public const string Header = "headers";
}

/// <summary>
///     
/// </summary>
public class Exchange : IExchange
{
    public Exchange(
           string name, 
           string type = ExchangeType.Direct, 
           bool durable = true, 
           bool autoDelete = false, 
           IDictionary<string, object> arguments = null)
    {
        Name = name ??
            throw new ArgumentNullException(name, $"{name} must not be null");

        Type = type;
        IsDurable = durable;
        IsAutoDelete = autoDelete;
        Arguments = arguments ?? new Dictionary<string, object>();
    }

    public string Name { get; }
    public string Type { get; }
    public bool IsDurable { get; }
    public bool IsAutoDelete { get; }
    public IDictionary<string, object> Arguments { get; }

    /// <summary>
    ///      Exchange  . 
    ///     Exchange   - direct exchnge  .
    ///         ,   
    ///         
    ///          .
    /// </summary>        
    public static IExchange GetDefault()
    {
        return new Exchange("");
    }
}

• RabbitMQ