BacklogTracer

Camel supports a backlog tracer interceptor that is used for capturing a trace message of each message as they are routed in Camel. The trace message is stored in a backlog queue, which contains the last N messages for each node in the routes (by default 10).

What is the difference between BacklogTracer and Tracer

Camel also provides a Tracer which has similar capabilities as this backlog tracer. The difference is that the backlog tracer is storing a capture of the message in an internal backlog queue.

The Tracer is event based and logs the messages as they happen (or route to another Camel destination).

Use the Tracer when all you need is to log the traced messages as they happen.

The backlog tracer allows you to pull the messages from the backlog queues on demand. The backlog tracer works better with JMX capable tooling as it is simpler, allowing to bulk dump all its traced messages in either a POJO or XML format.

Options

Option	Default	Description
standby	`false`	Whether the tracer is standby. If a tracer is in standby then the tracer is activated during startup and are ready to be enabled manually via JMX or calling the enabled method.
enabled	`false`	Flag to enable or disable this tracer
backlogSize	`100`	Maximum number of total traced messages to keep in the backlog (FIFO queue). Should be between 1 - 1000.
tracePattern	`null`	Allows to filter tracing using a pattern that matches against the node id and route id. For example use `"to1,to2"` to match only nodes with either the name "to1", or "to2". You can use * for wildcards. So you can do "to" to match any to. Or use "route-foo" to match any foo routes.
traceFilter	`null`	Allow to configure a filter as a Predicate using any of the Camel languages. But default the Simple language is used. For example to filter on messages with a given header, use `${header.foo} != null`. To use Groovy then prefix the value with "groovy:". And similar for the other languages.
traceRests	`false`	Whether tracing should trace inner details from Rest DSL. Turning this on increases the verbosity of tracing by including events from internal routes by Rest DSL.
traceTemplates	`false`	Whether tracing should trace inner details from route templates (or kamelets). Turning this on increases the verbosity of tracing by including events from internal routes in the templates or kamelets.
removeOnDump	`true`	Whether to remove the traced messages that was returned when invoking the dump methods.
bodyMaxChars	`32kb`	To limit the message body to a maximum size in the traced message. Use 0 or negative value to use unlimited size.
bodyIncludeStreams	`false`	Whether to include the message body of stream based messages. If enabled then beware the stream may not be re-readable later. See more about Stream Caching.
bodyIncludeFiles	`true`	Whether to include the message body of file based messages. The overhead is that the file content has to be read from the file.
includeExchangeProperties	`true`	Trace messages to include exchange properties.
includeExchangeVariables	`true`	Trace messages to include exchange variables.
includeException	`true`	Trace messages to include exception if the message failed.

Operations

Option	Default	Description
getTraceCounter	`long`	Gets the total number of traced messages.
getQueueSize	`long`	Number of traced messages in the backlog.
resetTraceCounter	`void`	To reset the trace counter.
dumpTracedMessages(nodeOrRouteId)	`List<BacklogTracerEventMessage>`	To dump the traced messages from the give node or route id.
dumpTracedMessagesAsXml(nodeOrRouteId)	`String`	To dump the traced messages from the give node or route id in XML format.
dumpTracedMessagesAsJSon(nodeOrRouteId)	`String`	To dump the traced messages from the give node or route id in JSon format.
dumpAllTracedMessages	`List<BacklogTracerEventMessage>`	To dump all the traced messages
dumpAllTracedMessagesAsXml	`String`	To dump all the traced messages in XML format.
dumpAllTracedMessagesAsJSon	`String`	To dump all the traced messages in JSon format.

Enabling

You can turn on backlog tracing on CamelContext

camelContext.setBacklogTracing(true);

And in Spring XML

<camelContext backlogTrace="true">
  ...
</camelContext>

And in Camel Main you can enable this in the application.properties file:

camel.trace.enabled = true

And in Spring Boot you can enable this in the application.properties file:

camel.trace.enabled = true

Tracing payloads of InputStream types

Beware that when enabling backlog tracing, and the message payloads is streaming types (such as java.io.InputStream), then the backlog tracer will read the payload and make a copy as a trace that are stored in the backlog tracer. Then monitoring tooling is able to view these traced events.

When working with InputStream types then Camel has Stream caching that is able to automatic make such types safe to use as they are cached and able to be re-read. See more details at Stream caching.

However, Camel’s stream caching is ONLY for message body. Having message headers of type InputStream is discouraged and not common use. If you add custom message headers, then it is recommended to NOT use streaming types, but convert these headers into String or byte[] or other standard Java types that are in-memory and safe to re-read.

Backlog Tracer