# Prometheus Plugs [![Hex.pm](https://img.shields.io/hexpm/v/prometheus_plugs.svg?maxAge=2592000?style=plastic)](https://hex.pm/packages/prometheus_plugs)
Elixir plugs for [prometheus.erl](https://github.com/deadtrickster/prometheus.erl)
***TL;DR*** [Example app](https://github.com/deadtrickster/prometheus-plugs-example)
## Plugs
Prometheus Plugs currently comes with two Plugs. One is for collecting http metrics while another provides endpoint for scraping by Prometheus daemon.
#### Plug.PrometheusCollector
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.
All metrics support configurable labels:
```elixir
# on app startup (e.g. supervisor setup)
Plug.PrometheusCollector.setup(labels: [:method, :host])
# in your plugs pipeline
plug Plug.PrometheusCollector, [:method, :host]
```
Supported labels include:
- 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)
In fact almost any [Plug.Conn](https://hexdocs.pm/plug/Plug.Conn.html) 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:
``` elixir
defmodule CustomLabels do
def connection_private_key(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
# As a key/value for the Collector
Plug.PrometheusCollector.setup(labels: [:method, :phoenix_controller]
plug Plug.PrometheusCollector, [:code, phoenix_controller: &CustomLabels.connection_private_key/2]
# As a simple fun
Plug.PrometheusCollector.setup(labels: [:method, :phoenix_controller_action]
plug Plug.PrometheusCollector, [:code, &CustomLabels.phoenix_controller_action/1]
```
Additionaly `http_request_duration_microseconds` supports configurable bucket bounds:
```elixir
Plug.PrometheusCollector.setup([labels: [:method, :host],
request_duration_bounds: [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]])
plug Plug.PrometheusCollector, [:method, :host]
```
Bear in mind that bounds are ***microseconds*** (1s is 1_000_000us)
#### Plug.PrometheusExporter
Exports metrics in text format via configurable endpoint:
``` elixir
# on app startup (e.g. supervisor setup)
Plug.PrometheusExporter.setup()
# in your plugs pipeline
plug Plug.PrometheusExporter, [path: "/prom/metrics"] # default is /metrics
```
## Installation
The package can be installed as:
1. Add prometheus_plug to your list of dependencies in `mix.exs`:
def deps do
[{:prometheus_plugs, "~> 0.7"}]
end
2. Ensure prometheus is started before your application:
def application do
[applications: [:prometheus]]
end
## License
MIT