Chapter 96. Metrics
Metrics Component
Available as of Camel 2.14
The metrics: component allows to collect various metrics directly from Camel routes. Supported metric types are counter, histogram, meter and timer. Metrics provides simple way to measure behaviour of application. Configurable reporting backend is enabling different integration options for collecting and visualizing statistics. The component also provides a
MetricsRoutePolicyFactory which allows to expose route statistics using codehale metrics, see bottom of page for details.
Maven users will need to add the following dependency to their
pom.xml for this component:
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-metrics</artifactId>
<version>x.x.x</version>
<!-- use the same version as your Camel core version -->
</dependency>URI format
metrics:[ meter | counter | histogram | timer ]:metricname[?options]
Metric Registry
Camel Metrics Component uses by default
MetricRegistry with Slf4jReporter and 60 second reporting interval. Default registry can be replaced with custom one by providing bean with name metricRegistry in Camel registry. For example using Spring Java Configuration.
@Configuration
public static class MyConfig extends SingleRouteCamelConfiguration {
@Bean
@Override
public RouteBuilder route() {
return new RouteBuilder() {
@Override
public void configure() throws Exception {
// define Camel routes here
}
};
}
@Bean(name = MetricsComponent.METRIC_REGISTRY_NAME)
public MetricRegistry getMetricRegistry() {
MetricRegistry registry = ...;
return registry;
}
}Warning
MetricRegistry uses internal thread(s) for reporting. There is no public API in version 3.0.1 for users to clean up on exit. Thus using Camel Metrics Component leads to Java classloader leak and my cause OutOfMemoryErrors in some cases.
Usage
Headers
Metric name defined in URI can be overridden by using header with name
CamelMetricsName.
For example
from("direct:in")
.setHeader(MetricsConstants.HEADER_METRIC_NAME, constant("new.name"))
.to("metrics:counter:name.not.used")
.to("direct:out");
will update counter with name
new.name instead of name.not.used.
All Metrics specific headers are removed from the message once Metrics endpoint finishes processing of exchange. While processing exchange Metrics endpoint will catch all exceptions and write log entry using level
warn.
Metrics type counter
metrics:counter:metricname[?options]
Options
|
Name
|
Default
|
Description
|
|
increment
|
-
|
Long value to add to the counter
|
|
decrement
|
-
|
Long value to subtract from the counter
|
If neither
increment or decrement is defined then counter value will be incremented by one. If increment and decrement are both defined only increment operation is called.
// update counter simple.counter by 7
from("direct:in")
.to("metric:counter:simple.counter?increment=7")
.to("direct:out");// increment counter simple.counter by 1
from("direct:in")
.to("metric:counter:simple.counter")
.to("direct:out");// decrement counter simple.counter by 3
from("direct:in")
.to("metric:counter:simple.counter?decrement=3")
.to("direct:out");Headers
Message headers can be used to override
increment and decrement values specified in Metrics component URI.
|
Name
|
Description
|
Expected type
|
|
CamelMetricsCounterIncrement
|
Override increment value in URI
|
Long
|
|
CamelMetricsCounterDecrement
|
Override decrement value in URI
|
Long
|
// update counter simple.counter by 417
from("direct:in")
.setHeader(MetricsConstants.HEADER_COUNTER_INCREMENT, constant(417L))
.to("metric:counter:simple.counter?increment=7")
.to("direct:out");// updates counter using simple language to evaluate body.length
from("direct:in")
.setHeader(MetricsConstants.HEADER_COUNTER_INCREMENT, simple("${body.length}"))
.to("metrics:counter:body.length")
.to("mock:out");Metric type histogram
metrics:histogram:metricname[?options]
Options
|
Name
|
Default
|
Description
|
|
value
|
-
|
Value to use in histogram
|
If no
value is not set nothing is added to histogram and warning is logged.
// adds value 9923 to simple.histogram
from("direct:in")
.to("metric:histogram:simple.histogram?value=9923")
.to("direct:out");// nothing is added to simple.histogram; warning is logged
from("direct:in")
.to("metric:histogram:simple.histogram")
.to("direct:out");Headers
Message header can be used to override value specified in Metrics component URI.
|
Name
|
Description
|
Expected type
|
|
CamelMetricsHistogramValue
|
Override histogram value in URI
|
Long
|
// adds value 992 to simple.histogram
from("direct:in")
.setHeader(MetricsConstants.HEADER_HISTOGRAM_VALUE, constant(992L))
.to("metric:histogram:simple.histogram?value=700")
.to("direct:out")Metric type meter
metrics:meter:metricname[?options]
Options
|
Name
|
Default
|
Description
|
|
mark
|
-
|
Long value to use as mark
|
If
mark is not set then meter.mark() is called without argument.
// marks simple.meter without value
from("direct:in")
.to("metric:simple.meter")
.to("direct:out");// marks simple.meter with value 81
from("direct:in")
.to("metric:meter:simple.meter?mark=81")
.to("direct:out");Headers
Message header can be used to override
mark value specified in Metrics component URI.
|
Name
|
Description
|
Expected type
|
|
CamelMetricsMeterMark
|
Override mark value in URI
|
Long
|
// updates meter simple.meter with value 345
from("direct:in")
.setHeader(MetricsConstants.HEADER_METER_MARK, constant(345L))
.to("metric:meter:simple.meter?mark=123")
.to("direct:out");Metrics type timer
metrics:timer:metricname[?options]
Options
|
Name
|
Default
|
Description
|
|
action
|
-
|
start or stop
|
If no
action or invalid value is provided then warning is logged without any timer update. If action start is called on already running timer or stop is called on not running timer then nothing is updated and warning is logged.
// measure time taken by route "calculate"
from("direct:in")
.to("metrics:timer:simple.timer?action=start")
.to("direct:calculate")
.to("metrics:timer:simple.timer?action=stop");TimerContext objects are stored as Exchange properties between different Metrics component calls.
Headers
Message header can be used to override action value specified in Metrics component URI.
|
Name
|
Description
|
Expected type
|
|
CamelMetricsTimerAction
|
Override timer action in URI
|
org.apache.camel.component.metrics.timer.TimerEndpoint.TimerAction
|
// sets timer action using header
from("direct:in")
.setHeader(MetricsConstants.HEADER_TIMER_ACTION, TimerAction.start)
.to("metric:timer:simple.timer")
.to("direct:out");MetricsRoutePolicyFactory
This factory allows to add a RoutePolicy for each route which exposes route utilization statistics using codehale metrics. This factory can be used in Java and XML as the examples below demonstrates.
Tip
Instead of using the MetricsRoutePolicyFactory you can define a MetricsRoutePolicy per route you want to instrument, in case you only want to instrument a few selected routes.
From Java you just add the factory to the
CamelContext as shown below:
context.addRoutePolicyFactory(new MetricsRoutePolicyFactory());
And from XML DSL you define a <bean> as follows:
<!-- use camel-metrics route policy to gather metrics for all routes --> <bean id="metricsRoutePolicyFactory" class="org.apache.camel.component.metrics.routepolicy.MetricsRoutePolicyFactory"/>
The
MetricsRoutePolicyFactory and MetricsRoutePolicy supports the following options:
|
Name
|
Default
|
Description
|
|
useJmx
|
false
|
Whether to report fine grained statistics to JMX by using the
com.codahale.metrics.JmxReporter. Notice that if JMX is enabled on CamelContext then a MetricsRegistryService mbean is enlisted under the services type in the JMX tree. That mbean has a single operation to output the statistics using json. Setting useJmx to true is only needed if you want fine grained mbeans per statistics type.
|
|
jmxDomain
|
org.apache.camel.metrics
|
The JMX domain name
|
|
prettyPrint
|
false
|
Whether to use pretty print when outputting statistics in json format
|
|
metricsRegistry
|
|
Allow to use a shared
com.codahale.metrics.MetricRegistry. If none is provided then Camel will create a shared instance used by the this CamelContext.
|
|
rateUnit
|
TimeUnit.SECONDS
|
The unit to use for rate in the metrics reporter or when dumping the statistics as json.
|
|
durationUnit
|
TimeUnit.MILLISECONDS
|
The unit to use for duration in the metrics reporter or when dumping the statistics as json.
|
From Java code tou can get hold of the
com.codahale.metrics.MetricRegistry from the org.apache.camel.component.metrics.routepolicy.MetricsRegistryService as shown below:
MetricRegistryService registryService = context.hasService(MetricsRegistryService.class);
if (registryService != null) {
MetricsRegistry registry = registryService.getMetricsRegistry();
...
}