.. SPDX-License-Identifier: GPL-3.0-or-later

.. _mod-http-prometheus:

Prometheus metrics endpoint
---------------------------

The :ref:`HTTP module <mod-http>` exposes ``/metrics`` endpoint that serves metrics
from :ref:`mod-stats` in Prometheus_ text format.
You can use it as soon as HTTP module is configured:

.. code-block:: bash

	$ curl -k https://localhost:8453/metrics | tail
	# TYPE latency histogram
	latency_bucket{le=10} 2.000000
	latency_bucket{le=50} 2.000000
	latency_bucket{le=100} 2.000000
	latency_bucket{le=250} 2.000000
	latency_bucket{le=500} 2.000000
	latency_bucket{le=1000} 2.000000
	latency_bucket{le=1500} 2.000000
	latency_bucket{le=+Inf} 2.000000
	latency_count 2.000000
	latency_sum 11.000000

You can namespace the metrics in configuration, using `http.prometheus.namespace` attribute:

.. code-block:: lua

        modules.load('http')
        -- Set Prometheus namespace
        http.prometheus.namespace = 'resolver_'

You can also add custom metrics or rewrite existing metrics before they are returned to Prometheus client.

.. code-block:: lua

        modules.load('http')
        -- Add an arbitrary metric to Prometheus
        http.prometheus.finalize = function (metrics)
        	table.insert(metrics, 'build_info{version="1.2.3"} 1')
        end

.. _Prometheus: https://prometheus.io