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Metricsd

I am a metrics aggregator for Graphite that supports counters, histograms and meters.

I should be drop-in compatible with Etsy's statsd, although I add explicit support for meters (with the m type) and gauges (with the g type) and introduce the h (histogram) type as an alias for timers (ms). I make heavy use of Coda Hale / Yammer's Metrics library for the JVM, including its ability to flush to Graphite.

As with statsd, all values (excepting sample rate) are expected to be integers. Go forth and multiply.

Meters are assumed to be per-second.

Metrics will be published to Graphite in the form metrics.{counter,gauge,histogram,meter}.<metric name>.<metric>. Multiple metrics may be published by joining messages together with newlines (as with statsite).

In addition to the Metrics library, I owe a great deal of gratitude to statsd (both Etsy's and Flickr's) and James Golick's statsd.scala for paving the way, in my protocol and structure respectively.

Metric Types

Metrics are collected by sending UDP messages to metricsd on port 8125 (or whatever you've overridden it to be).

For testing purposes, you can use netcat:

echo "varietiesOfCheese:12|c" | nc -w 0 -u localhost 8125

When instrumenting your application, you'll probably want to use one of the statsd-compatible libraries.

Counters

Counters are incremented/decremented by sending messages of the form:

<metric name>:<value>|c

For example, to add 12 varieties to the "varietiesOfCheese" metric:

varietiesOfCheese:12|c

Counters may be updated at a lower sample rate; to do so, add |@<sample rate>, e.g.:

varietiesOfCheese:3|c|@0.25

N.B.: Counters are currently reset when metricsd starts up. If you need long-term historical values, you should use a gauge instead.

Gauges

Gauges are updated by sending messages of the form:

<metric name>:<value>|g

For example, to set the current value for "varietiesOfCheese":

varietiesOfCheese:27|g

As gauges do not have base their current value on previous values, they are more appropriate for storing metrics in a durable fashion (i.e. not susceptible to metricsd restarting).

Histograms

Histograms are updated by sending messages of the form:

<metric name>:<value>|h

For example:

responseTime:244|h

Again, values must be integers, so use a data-appropriate scale (e.g. milliseconds).

N.B.: Histograms will be reset (samples will be cleared) when metricsd restarts. Biased (ExponentiallyDecayingSample(1028, 0.015), Metrics' HistogramMetric.SampleType.BIASED, biasing the sample to the last 5 minutes) histograms are used to mitigate the impact of this.

Meters

Meters are updating by sending messages of the form:

<metric name>

For example:

userDidSignIn

Deleting Metrics

From time to time you may submit erroneous metrics or find that you're no longer interesting in tracking older metrics. Rather than restarting the server to clear metricsd's memory of them (and losing the state of your counters), you can send additional messages to delete them:

<metric name>:delete|<metric type>

For example, to delete a typo'd repsonseTime histogram:

repsonseTime:delete|h

This can also be done from the command line:

echo "repsonseTime:delete|h" | nc -w 0 -u localhost 8125

Management

metricsd provides a simple, text-based interface (telnet-like) interface to obtain information about known metrics. This interface runs on a separate port (8126 by default).

The following commands are supported:

  • help - Provides a list of known commands
  • counters - Lists known counters
  • gauges - Lists known gauges
  • histograms - Lists known histograms
  • meters - Lists known meters
  • quit - Closes the connection

Each command should be followed by a newline to execute.

For the commands that list metrics, each metric name will be followed by a newline and the list itself will be terminated by END with two newlines following.

echo "varietiesOfCheese:1|c" | nc -w 0 -u localhost 8125
echo "varietiesOfMice:2|c" | nc -w 0 -u localhost 8125
echo "cheeseEaten:2|h" | nc -w 0 -u localhost 8125

$ telnet localhost 8126
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
counters
varietiesOfMice
varietiesOfCheese
END

histograms
cheeseEaten
END

gauges 
END

quit
Connection closed by foreign host.

Running

To run metricsd, execute the JAR:

$ java -jar metricsd-<version>-jar-with-dependencies.jar

If you wish to provide a custom configuration:

$ CONFIG=/path/to/config.json java -jar metricsd-<version>-jar-with-dependencies.jar

Configuration

Configuration is done by providing the path to a JSON file similar to config/metricsd.json:

{
    "debug": false,
    "graphite": {
        "flushInterval": 10,
        "host": "localhost",
        "port": 2003
    },
    "log": {
        "level": "INFO",
        "file": "log/metricsd.log"
    },
    "port": 8125,
    "prefix": "metricsd",
    "managementPort": 8126
}

These are the default values; feel free to omit unchanged values from your configuration.

Installing

Seth is experimenting with maintaining a PPA for Ubuntu packages.

Building

Build Requirements

  • Scala 2.9.1
  • Maven 3.0.x

Begin by installing Scala and Maven according to the relevant instructions for your system.

To build a packaged JAR containing dependencies:

$ mvn package

Packages

Debian packaging lives in a bzr repository on Launchpad: ~mojodna/+junk/metricsd-package

License

Copyright (c) 2011 Seth Fitzsimmons

Published under the BSD License.