### Initialize TelemetryMetricsPrometheus under a Supervisor

Source: https://hexdocs.pm/telemetry_metrics_prometheus

This snippet shows how to start TelemetryMetricsPrometheus as a child process within an Elixir application's supervision tree. It includes a list of metrics to monitor.

```elixir
def start(_type, _args) do
  # List all child processes to be supervised
  children = [
    {TelemetryMetricsPrometheus, [metrics: metrics()]}
  ...
  ]

  opts = [strategy: :one_for_one, name: ExampleApp.Supervisor]
  Supervisor.start_link(children, opts)
end

defp metrics, do:
  [
    counter("http.request.count"),
    sum("http.request.payload_size", unit: :byte),
    last_value("vm.memory.total", unit: :byte)
  ]
```

--------------------------------

### Start TelemetryMetricsPrometheus Reporter

Source: https://hexdocs.pm/telemetry_metrics_prometheus

This function starts the TelemetryMetricsPrometheus reporter and links it to the calling process. It accepts various options to configure metrics, port, protocol, and handlers.

```elixir
start_link(options()) :: GenServer.on_start()
```

--------------------------------

### Define a Prometheus Metrics Distribution

Source: https://hexdocs.pm/telemetry_metrics_prometheus

Example of defining a distribution metric for Prometheus, specifically for tracking the duration of prometheus metrics scrapes. It configures buckets, event name, measurement, tags, and units.

```elixir
Metrics.distribution("prometheus_metrics.scrape.duration.milliseconds",
  reporter_options: [buckets: [0.05, 0.1, 0.2, 0.5, 1]],
  description: "A histogram of the request duration for prometheus metrics scrape.",
  event_name: [:prometheus_metrics, :plug, :stop],
  measurement: :duration,
  tags: [:name],
  tag_values: fn %{conn: conn} ->
    %{name: conn.private[:prometheus_metrics_name]}
  end,
  unit: {:native, :millisecond}
)
```

--------------------------------

### Get Reporter's Child Specification

Source: https://hexdocs.pm/telemetry_metrics_prometheus

Provides a child specification for the TelemetryMetricsPrometheus reporter, suitable for use with Elixir's Supervisor module. This allows the reporter to be supervised within an application.

```elixir
child_spec(options()) :: Supervisor.child_spec()
```

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