Prometheus Plugs

Plugs

Prometheus Plugs currently comes with two Plugs. One is for collecting http metrics while another provides endpoint for scraping by Prometheus daemon.

Prometheus.PlugsInstrumenter

Currently maintains two metrics.

http_requests_total - Total nubmer of HTTP requests made. This one is a counter.
http_request_duration_microseconds - The HTTP request latencies in microseconds. This one is a histogram.

Setup

# on app startup (e.g. supervisor setup)
Prometheus.PlugsInstrumenter.setup()

# in your plugs pipeline
plug Prometheus.PlugsInstrumenter

Plugs instrumenter can be configured via PlugsInstrumenter key of prometheus app env.

All metrics support configurable labels:

status_code - http code
status_class - http code class, like "success", "redirect", "client-error", etc
method - http method
host - requested host
port - requested port
scheme - request scheme (like http or https)

Default configuration:

config :prometheus, PlugsInstrumenter,
  labels: [:status_class, :method, :host, :scheme],
  duration_buckets:[10, 100, 1_000, 10_000, 100_000,
                    300_000, 500_000, 750_000, 1_000_000,
                    1_500_000, 2_000_000, 3_000_000],
  registry: :default

In fact almost any Plug.Conn field value can be used as metric label. In order to create a custom label simply provide a fun as either a key-value pair where the value is a fun which will be given the label and conn as parameters:

defmodule CustomLabels do
  def label_value(key, conn) do
    Map.get(conn.private, key, "unknown") |> to_string
  end

  def phoenix_controller_action(%Plug.Conn{private: private}) do
    case [private[:phoenix_controller], private[:phoenix_action]] do
      [nil, nil] -> "unknown"
      [controller, action] -> "#{controller}/#{action}"
    end
  end
end

labels: [:status_class, phoenix_controller: CustomLabels, phoenix_controller_action: {CustomLabels, :phoenix_controller_action}]

Bear in mind that bounds are microseconds (1s is 1_000_000us)

Plug.PrometheusExporter

Exports metrics in text format via configurable endpoint:

# on app startup (e.g. supervisor setup)
Plug.PrometheusExporter.setup()

# in your plugs pipeline
plug Plug.PrometheusExporter

Defautl Configuration:

config :prometheus, PlugsExporter,
  path: "/metrics",
  format: :text,
  registry: :default

Installation

The package can be installed as:

Add prometheus_plug to your list of dependencies in mix.exs:
def deps do
```
 [{:prometheus_plugs, "~> 0.7"}]
```
end
Ensure prometheus is started before your application:
def application do
```
 [applications: [:prometheus]]
```
end

License

MIT