ExStatsD

A statsd client implementation for Elixir.

Usage

Add ExStatsD as a dependency for your application.

defp deps do
  [{:ex_statsd, ">= 0.5.1"}]
end

You should also update your applications list to include statsd:

def application do
  [applications: [:ex_statsd]]
end

Configure ex_statsd using Mix.Config as usual (probably in your config/):

use Mix.Config

config :ex_statsd,
       host: "your.statsd.host.com",
       port: 1234,
       namespace: "your-app"

The defaults are:

• host: 127.0.0.1
• port: 8125
• namespace: nil

The following are the basic metric types. Additional features are described in "Extensions," below.

Counters

Counters can be manipulated with ExStatsD.increment/1 and ExStatsD.decrement/1 for simple counts:

if passed? do
  ExStatsD.increment("cases.passed")
end

if cancelled_account? do
  ExStatsD.decrement("users")
end

You can also provide a sample_rate with ExStatsD.increment/2 and ExStatsD.decrement/2. For example, in this case an increment for cart.added will only be sent 50% of the time:

ExStatsD.increment("cart.added", sample_rate: 0.5)

To set a counter explicitly, use ExStatsD.counter/2:

3 |> ExStatsD.counter("cart.removed")

You can also send a sample_rate:

3 |> ExStatsD.counter("cart.removed", sample_rate: 0.25)

Note that the function returns the value (eg, 3 here), making it suitable for pipelining.

Timers

Manually timed values can be recorded with ExStatsD.timer/2:

elapsed_ms = # something manually timed in
elapsed_ms |> ExStatsD.timer("foobar")

The value passed to ExStatsD.timer/2 (eg, elapsed_ms here) is returned from it, making this suitable for pipelining.

For convenience, you can also time a function call with ExStatsD.timing/2:

ExStatsD.timing "foo.bar", fn ->
  # Time something
end

To sample (ie, 50% of the time), pass a sample_rate:

ExStatsD.timing "foo.bar", fn ->
  # Time something, some of the time
end, sample_rate: 0.5

Note that, regardless of the sample rate, the function is always called -- it's just not always measured. Also note that the return value of the measured function is returned, making this suitable for pipelining.

Sets

A value can be recorded in a set with ExStatsD.set/2:

user_id |> ExStatsD.set("users")

Note that the function returns the value, making it suitable for pipelining.

Extensions

Datadog

Tags

All metrics support the Datadog-specific tags extension to StatsD. If you are using DogStatsD, you may provide a tags option, eg:

ExStatsD.increment("cart.added", tags: ~w(foo bar))

Histograms

The histogram extension to StatsD is supported for DogStatsD:

42 |> ExStatsD.histogram("database.query.time", tags: ["db", "perf"])

Note that the function returns the value, making it suitable for pipelining.

Histogram Timing

A histogram version of the ExStatsD.timing function is supported for DogStatsD.

ExStatsD.histogram_timing "foo.bar", fn ->
  # Time something
end

Decorators

The decorators allow you to quickly and easily time function calls in your code. Simply replace def with deftimed for those functions you wish to time.

defmodule MyModule.Data do
  use ExStatsD.Decorator

  deftimed slow_function do
    # This is a suspect function we wish to time.
  end

end

Now all calls to MyModule.Data.slow_function/0 will be timed and reported to your statsd server. By default the metric key used for each call will be PREFIX.function_call.MODULE.FUNCTION_ARITY. So in this example it would have been function_call.mymodule.data.slow_function_0.

You can change the metric name by setting the @metric attribute ahead of the function. The metric will apply to other function definitions of the same arity unless specifically changed again. Other following functions of different name or arity will use the default.

deftimed init, do: nil # PREFIX.function_call.mymodule.data.init_0

@metric "trace.some_function"
deftimed some_function(1), do: nil # PREFIX.trace.some_function
deftimed some_function(2), do: nil # PREFIX.trace.some_function

@metric "trace.some_function_catchall"
deftimed some_function(x) when is_list(x), do: nil # PREFIX.trace.some_function_catchall
deftimed some_function(x), do: nil # PREFIX.trace.some_function_catchall

deftimed some_function(x,y), do: nil # PREFIX.function_call.mymodule.data.some_function_2

You can set options using the @metric_options attribute. This follows the same rules as with the @metric example abobe.

Here we use Datadog's "tag" extension to StatD:

@metric_options [tags: ["basic"]]
deftimed some_function(), do: nil

There are 2 global options available. Both will apply to all functions that follow it unless locally overridden.

• @default_metric_options: Metric options to use unless overridden with @metric_options. Defaults to [].
• @use_histogram: Send results using histograms instead of gauges. For use with Datadog's DogStatD. Defaults to false.

Starting your own ExStatsD Server

There may be use cases where you need several ExStatsD instances. You may have several namespaces you need to send stats to, or maybe you have multiple statsd services you need to publish to.

To achieve this you can manually start a ExStatsD instance.

  {:ok, _first_pid} = ExStatsD.start_link([name: :first, namespace: "first.namespace"])

  {:ok, _second_pid} = ExStatsD.start_link([name: :second, namespace: "second.namespace"])

  ExStatsD.increment("the.thing", name: :first) # nil
  ExStatsD.increment("another.thing", name: :second) # nil

Of course, it's your own responsibility to supervise these servers.

To do that, you can use Supervisors

defmodule StatsDSupervisor do
  use Supervisor

  def start_link do
    Supervisor.start_link(__MODULE__, [])
  end

  def init(_) do
    children = [
      worker(ExStatsD, [[name: :first_name, namespace: "first.namespace"]], [id: "first_id"]),
      worker(ExStatsD, [[name: :second_name, namespace: "second.namespace"]], [id: "second_id"])
    ]

    options = [
      strategy: :one_for_one, name: StatsDSupervisor
    ]

    supervise(children, options)
  end
end

The items that can be overridden include

• port
• host
• namespace
• sink

License

The MIT License (MIT)

Copyright (c) 2014 CargoSense, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.