Watchman

Watchman is your friend who monitors your processes so you don't have to.

Installation

Add the following to the list of your dependencies:

def deps do
  [
    {:watchman, github: "renderedtext/ex-watchman"}
  ]
end

Also, add it to the list of your applications:

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

Setup

First, set up the host and the port of the metrics server, and the prefix you want to use. Example:

config :watchman,
  host: "statistics.example.com",
  port: 22001,
  prefix: "my-service.prod"

Usage

To submit a simple value from your service:

Watchman.submit("users.count", 30)

To increment a simple value from your service:

Watchman.increment("users.count")

to decrement:

Watchman.decrement("users.count")

You can also use the count annotation. Placed in front of a method, it will count the number of times the method was called.

To count a method with an auto generated key in your module:

defmodule Example do
  use Watchman.Count

  @count(key: :auto)
  def test
    :timer.sleep(10)
  end

end

To count a method while giving the metric a key:

defmodule Example do
  use Watchman.Count

  @count(key: "lazy.test.function.that.only.sleeps.count")
  def test
    :timer.sleep(10)
  end

end

To submit a timing value:

Watchman.submit("installation.duration", 30, :timing)

For timing services you can use the benchmark feature.

To benchmark a part of your service:

Watchman.benchmark("sleep.duration", fn ->
  IO.puts "Sleeping"
  :timer.sleep(10000)
  IO.puts "Wake up"
end)

To benchmark a function with an auto generated key in your module:

defmodule Example do
  use Watchman.Benchmark

  @benchmark(key: :auto)
  def test
    :timer.sleep(10)
  end

end

To benchmark a function while giving the metric a key:

defmodule Example do
  use Watchman.Benchmark

  @benchmark(key: "lazy.test.function.that.only.sleeps.benchmark")
  def test
    :timer.sleep(10)
  end

end

Please note that if the key is manually given, it cannot contain blank spaces. Also, if you want to use both the benchmark and the count annotations, you can just write:

use Watchman

instead of:

use Watchman.Benchmark
use Watchman.Count

To keep track if the application is running, use the heartbeat feature. Define a child process in the supervisor with a defined interval between notifications (in seconds), like so:

worker(Watchman.Heartbeat, [[interval: 1]])