Channels | RabbitMQ

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https://www.rabbitmq.com/docs/channels

For simplicity and ease of infrastructure management, there is only ever a single TCP connection to rabbit.

Channels exist as a sort of virtual connection to rabbit, and each acts independently of the others.

Code

Opening a Channel

var connectionFactory = new ConnectionFactory();

var connection = await connectionFactory.CreateConnectionAsync();

var channel = await connection.CreateChannelAsync();

// ... use the channel to declare topology, publish, consume

Closing a Channel

If a message has been consumed then marked as Ack’ed after the channel is closed, the message will be re-queued. Thus you must ensure you close the channel when it is no longer needed.

// create channel

// do some work

// close the channel when it is no longer needed

await channel.CloseAsync();

Error Handling

Channels may fail or close for multiple reasons; rabbit often has a “soft-failure” approach allowing you to see why the failure happened, and gives you the opportunity to recover. The following handlers may be implemented.

channel.CallbackExceptionAsync += async (_, args) =>
{
    Console.WriteLine(args.Exception);
    await Task.CompletedTask;
};

channel.ChannelShutdownAsync += async (_, args) =>
{
    Console.WriteLine(args.ReplyText);
    await Task.CompletedTask;
};

Management

Channel Leak

When a channel is not closed, resulting in a open channel that is not being used. This consumes the channel count and can lead to large issues.

High Channel Churn

When channels are open and closed rapidly. A count higher than 100/second is pretty bad, and indicates sub-optimal performance.

Channels should be open for as long as possible while they are needed.