README.md

PrometheusTelemetry

PrometheusTelemetry is the plumbing for Telemetry.Metrics and allows the metrics passed in to be collected and exported in the format expected by the prometheus scraper.

This supervisor also contains the ability to spawn an exporter which will scrape every supervisor running for metrics and will spin up a plug and return it at /metrics on port 4050 by default, this will work out of the box with umbrella apps as well and allow you to define metrics in each umbrella app

Installation

The package can be installed by adding prometheus_telemetry to your list of dependencies in mix.exs:

def deps do
  [
    {:prometheus_telemetry, "~> 0.1.0"}
  ]
end

Documentation can be found at https://hexdocs.pm/prometheus_telemetry.

Example

We can add this to any application we want:

children = [
  {PrometheusTelemetry, metrics: [
   MyMetricsModule.metrics()
  ]}
]

Then to setup an exporter, on a server application like a phoenix app or pipeline we can setup the exporter which will start the metrics server (by default on port localhost:4050):

children = [
  {PrometheusTelemetry,
    exporter: [enabled?: true],
    metrics: MyMetricsModule.metrics()
  }
]

Built in Metrics

There are built in metrics for some erlang vm stats, phoenix, absinthe and ecto, to enable them we can use the following modules PrometheusTelemetry.Metrics.Ecto, PrometheusTelemetry.Metrics.Phoenix, PrometheusTelemetry.Metrics.GraphQL and PrometheusTelemetry.Metrics.VM

children = [
  {PrometheusTelemetry,
    exporter: [enabled?: true],
    metrics: [
      PrometheusTelemetry.Metrics.Ecto.metrics(),
      PrometheusTelemetry.Metrics.Phoenix.metrics(),
      PrometheusTelemetry.Metrics.GraphQL.metrics(),
      PrometheusTelemetry.Metrics.VM.metrics()
    ]
  }
]

Defining Custom Metrics

To define metrics we can create a module to group them like MyMetricsModule

defmodule MyMetricsModule do
  import Telemetry.Metrics, only: [last_value: 2, counter: 2]

  def metrics do
    [
      counter(
        "prometheus_name.to_save", # becomes prometheus_name_to_save in prometheus
        event_name: [:event_namespace, :my_metric], # telemetry event name
        measurement: :count, # telemetry event metric
        description: "some description"
      ),

      last_value(
        "my_custom.name",
        event_name: [:event_namespace, :last_value],
        measurement: :total,
        description: "my value",
        tags: [:custom_metric] # custom metrics to save, derived from :telemetry.execute metadata
      )
    ]
  end

  def inc_to_save do
    :telemetry.execute([:event_namespace, :my_metric], %{count: 1})
  end

  def set_custom_name do
    :telemetry.execute([:event_namespace, :last_value], %{total: 123}, %{custom_metric: "region"})
  end
end

Ultimately every list will get flattened which allows you to group metric modules under a single module such as

defmodule GraphQL.Request do
  def metrics do
    ...
  end
end

defmodule GraphQL.Complexity do
  def metrics do
    ...
  end
end

defmodule GraphQL do
  def metrics, do: [GraphQL.Complexity.metrics(), GraphQL.Request.metrics()]
end

For more details on types you can check telemetry_metrics_prometheus_core

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