log4net RabbitMQ Appender

note: I would recommend looking at Logary for a future-proof way of logging - while it doesn't have RabbitMQ support right now, adding it could be done in an hours worth of coding for a newbie, by following the structure of this repo or that of NLog.RabbitMQ.

Nuget key: log4net.RabbitMQAppender

An appender for logging over AMQP, specifically RabbitMQ. Why? Because sometimes you want to log with topics, without deciding on where the data/logs end up. Publish-subscribe, that is. The appender uses topics; a tutorial on topic routing, can be found at RabbitMQ's web site.

Appender properties:

• VHost - string - the virtual host to use. This needs to be configured in RabbitMQ before put to use. Defaults to /.
• UserName - string - the username to authenticate with. Defaults to guest.
• Password - string - the password to authenticate with. Defaults to guest.
• Port - uint - what port the RabbitMQ broker is listening to. Defaults to 5672.
• Topic - string - what topic to publish with. It must contain a string: {0}, or the logger won't work. The string inserted here will be used together with string.Format.
• Protocol - IProtocol - what protocol to use for RabbitMQ-communication. See also SetProtocol.
• HostName - string - the host name of the computer/node to connect to. Defaults to localhost.
• Exchange - string - what exchange to publish log messages to. Defaults to app-logging and is declared when the appender is started.
• ExchangeProperties - ExchangeProperties - defines exchange properties.
• MessageProperties - MessageProperties - defines message properties.
• AppId - string - the name of the publishing application
• ExtendedData - bool - whether to include the class, file and the line of the log message as headers in IBasicProperties.

ExchangeProperties allow you to customize the RabbitMQ exchange messages are published to. These properties are typically used when the exchange is declared and initialized:

• Name - string - what exchange to publish log messages to. Defaults to app-logging and is declared when the appender is started. This is an alternative to the appender Exchange property.
• ExchangeType - string - the exchange type. Defaults to topic. Used when the exchange is declared when the appender is started.
• Durable - bool - the exchange durability. Defaults to false. Used when the exchange is declared when the appender is started.
• Binding - ExchangeBinding - defines a binding between our Exchange and another exchange in RabbitMQ. Multiple bindings are allowed.

ExchangeBinding allow you to define a binding between our exchange and another RabbitMQ exchange:

• Destination - string - The name of the exchange to bind to.
• Topic - string - The topic (routing key) assoicated with the binding.

MessageProperties allow you to customize the message headers when publishing messages to RabbitMQ:

• AppId - string - The name of the publishing application. Alternative to the appender AppId property.
• Topic - LayoutPattern - topic format string to publish with. Superceeds the appender Topic property if set.
• ContentType - 'LayoutPattern' - Default is 'text/plain'.
• Persistent - 'bool' - Sets the message delivery mode. Default value is false (non-persistent).
• Priority - 'LayoutPattern' - Must resolve to a byte in the range 0 - 9. Default value is 0.
• ExtendedData - bool - whether to include the class, file and the line of the log message as headers in IBasicProperties. Alternative to the appender ExtendedData property.

For SSL -- have a look at: http://www.rabbitmq.com/ssl.html

A guide to setting up a secure corporate messaging infrastructure w/ .Net might be in the works... ;) Keep tuned to @henrikfeldt on twitter!

Example log4net.config

This configuration demonstrates usage of the properties from above:

<log4net>
	<appender name="AmqpAppender" type="log4net.RabbitMQ.RabbitMQAppender, log4net.RabbitMQ">
		<exchangeProperties>
			<name value = "app-logging" />
			<exchangeType value = "topic" />
			<durable value = false />
			<binding>
				<destination value="SomeOtherRabbitMQExchange" />
				<topic value="#" />
			</binding>
		</exchangeProperties>

		<messageProperties>
			<appId value="My Web Application" />
			<topic type="log4net.Layout.PatternLayout">
				<conversionPattern value="samples.web.%level" />
			</topic>
			<contentType type="log4net.Layout.PatternLayout">
				<conversionPattern value="text/plain" />
			</contentType>
			<persistent value = "false" />
			<priority type="log4net.Layout.PatternLayout">
				<conversionPattern value="0" />
			</priority>
			<extendedProperties value="true" />
		</messageProperties>

		<layout type="log4net.Layout.PatternLayout">
				<conversionPattern value="%date [%thread] %-5level - %message%newline" />
		</layout>
	</appender>
	<root>
		<level value="DEBUG"/>
		<appender-ref ref="AmqpAppender" />
	</root>
</log4net>

You would register log4net in a web application as such, in Application_Start:

using log4net.Config;
// ...
XmlConfigurator.ConfigureAndWatch(new FileInfo(Server.MapPath("~/log4net.config")));

In Application_End:

LogManager.Shutdown();

If you put the log4net configuration in web.config, reloading and restarting the AMQP channel won't work after an AppDomain recycle or change to the web.config file.

From the receiving side

For full documentation, see the RabbitMQ web site. An example receiver has this main method:

private static void Main(string[] args)
{
	var factory = new ConnectionFactory
	{
		HostName = "localhost",
		UserName = "guest",
		Password = "guest",
		Protocol = Protocols.DefaultProtocol
	};

	using (var c = factory.CreateConnection())
	using (var m = c.CreateModel())
	{
		var consumer = new QueueingBasicConsumer(m);
		var q = m.QueueDeclare("", false, true, true, null);

		m.QueueBind(q, "app-logging", "#");
		m.BasicConsume(q, true, consumer);
				
		while (true)
			Console.Write(((BasicDeliverEventArgs) consumer.Queue.Dequeue()).Body.AsUtf8String());
	}
}
// ...
static class Extensions {
	public static string AsUtf8String(this byte[] args) {
		return Encoding.UTF8.GetString(args);
	}
}

It should be noted that the message's IBasicProperties' following properties are also set:

• ContentEncoding - to "utf8"
• ContentType - default is "text/plain". Can be overridden in the MessageProperties.
• AppId - to loggingEvent.Domain. Can be overridden in the MessageProperties.
• Timestamp - to new AmqpTimestamp(Convert.ToInt64((loggingEvent.TimeStamp - _Epoch).TotalSeconds)) where _Epoch is 1/1/1970 at 00:00. Hence, it's the unix timestamp of when the log event happened in the application, according to that application's clock.

Furthermore, if ExtendedData (default false) is set to true (<extendedData value="true" />), these headers are set:

• Headers["ClassName"] - to the name of the class performing the logging
• Headers["FileName"] - to the name of the file where the logger resides
• Headers["MethodName"] - to the name of the method performing the logging
• Headers["LineNumber"] - to the line number of the code performing the logging

Final Remarks

Report issues at this repository's Issues page.

E-mail feedback to henrik at haf dot se or send me a pm over github.

Cheers, Henrik Feldt