Chapter 92. 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

Each metric has type and name. Supported types are counter, histogram, meter and timer. Metric name is simple string. If metric type is not provided then type meter is used by default.

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();
  ...
}