Add Prometheus Exporter docs

index.rst

@@ -21,6 +21,7 @@ NOTE: There are multiple options for reading this documentation. See link to the
    pages/configuration
    pages/secure/securing
    pages/sending_data
+   pages/metrics
    pages/sidecar
    pages/queries
    pages/streams

pages/metrics.rst

@@ -0,0 +1,158 @@
+*******
+Metrics
+*******
+
+Standard Metrics
+================
+
+Graylog collects metrics throughout its operation and stores them in-memory on each Graylog node. The metrics include
+event counts, timers and statistics for many parts of the Graylog application and its subsystems. Standard metrics are
+viewable within Graylog on the **System > Nodes** page through the **Metrics** button.
+
+.. image:: /images/metrics/standard_metrics.png
+
+Standard metrics can also be queried through the :ref:`Graylog REST API Browser <configuring_api>`.
+
+Prometheus Metric Exporting
+===========================
+
+Starting in Graylog 4.1, metrics can be exported to other systems via the Prometheus Metrics Exporting feature.
+This feature can be optionally enabled. When enabled, Graylog will export metrics via a standard
+`Prometheus HTTP exporter <https://prometheus.io/docs/instrumenting/writing_exporters>`_ on port ``9833``. Prometheus
+can then scrape and ingest the metrics.
+
+Configuration
+-------------
+
+To begin exporting Prometheus metrics, enable it with the following configuration property in the ``server.conf`` file.
+
+.. code-block::
+
+    prometheus_exporter_enabled = true
+
+Once enabled, metrics are exported in the `standard export format <https://prometheus.io/docs/instrumenting/writing_exporters/>`_ on the following URI by default.
+
+.. code-block::
+
+    http://127.0.0.1:9833/api/metrics/prometheus
+
+To specify a custom export hostname or IP address, the following configuration can be used.
+We suggest leaving the default export port `9833`, since it is already `registered with Prometheus <https://github.com/prometheus/prometheus/wiki/Default-port-allocations>`_.
+
+.. code-block::
+
+    prometheus_exporter_bind_address = 10.0.0.1:9090
+
+Depending on the Prometheus `scrape_config <https://eus.io/docs/prometheus/latest/configuration/configuration/#scrape_config>`_
+setting, an explicit scrape target might need to be specified in your Prometheus target hosts configuration.
+
+Default Core Metric Mappings
+----------------------------
+
+A `pre-defined core set <https://github.com/Graylog2/graylog2-server/blob/master/graylog2-server/src/main/resources/prometheus-exporter.yml>`_  of Graylog-to-Prometheus metric mappings are enabled by default.
+
+All metric names are prefixed with ``gl_...`` to clearly indicate that the metrics originated from Graylog. For example,
+the metric name ``gl_input_throughput``.
+
+.. image:: /images/metrics/prometheus_metric_names.png
+
+All metrics are automatically assigned a ``node`` `metric label <https://prometheus.io/docs/practices/naming/>`_,
+which contains the Graylog Node ID where the metric originated from. This can be useful for visualizing
+the same metric across Graylog nodes.
+
+.. image:: /images/metrics/node_id_metric.png
+
+Many metrics are exported with a consolidated name, which allows breakouts by labels to allow easier visualization of metrics.
+
+See the `pre-defined metric mappings <https://github.com/Graylog2/graylog2-server/blob/master/graylog2-server/src/main/resources/prometheus-exporter.yml>`_
+for a full list of metric mappings.
+
+
+Customized Metric Mappings
+--------------------------
+
+We understand that metric mapping requirements can be very specific the each per-customer use case, so we provide
+the ability to override the default core mappings. We also support the ability to specify any additional needed mappings.
+
+Graylog metrics exports heavily utilize `Prometheus labels <https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels>`_ to help you effectively visualize and analyze your metrics
+data.
+
+To completely replace the default core Prometheus mappings, provide the path to a core replacement mapping file ``YML`` file
+containing just the desired mappings with the following configuration property. This file is monitored for changes at
+runtime, so you can customize as needed without restarting your Graylog server. The file path is interpreted
+relative to the Graylog server working directory. Absolute paths are also supported.
+
+.. code-block::
+
+   prometheus_exporter_mapping_file_path_core = prometheus-exporter-mapping-core.yml
+
+To provide mappings in addition to the core defaults, provide the path to an additional mapping file ``yaml`` file
+containing the additional desired mappings with the following configuration property. This file is also monitored for
+changes at runtime.
+
+.. code-block::
+
+    prometheus_exporter_mapping_file_path_custom = prometheus-exporter-mapping-custom.yml
+
+Custom Mappings Format Example 1
+--------------------------------
+
+This example mapping produces the ``gl_stream_incoming_messages`` metric in Prometheus, which shows the number of
+messages received by for each stream in Graylog.
+
+The standard metric name in Graylog contains the ID of the stream, and one distinct metric is recorded for each stream.
+
+For example::
+
+    org.graylog2.plugin.streams.Stream.stream-1.incomingMessages
+    org.graylog2.plugin.streams.Stream.stream-2.incomingMessages
+    org.graylog2.plugin.streams.Stream.stream-3.incomingMessages
+
+The mapping definition that follows provides a ``match_pattern`` with a wildcard ``*`` for the ``stream-id``, which
+provides one label for each stream id automatically. This allows for the visualization of messages received for all
+streams together, but broken-out by stream-id via the labels functionality. The ``wildcard_extract_labels`` is an ordered
+array, which provides the label names for any specified wildcards in the ``match_pattern``.
+
+Mapping Definition::
+
+  - metric_name: "stream_incoming_messages"
+    match_pattern: "org.graylog2.plugin.streams.Stream.*.incomingMessages"
+    wildcard_extract_labels:
+      - "stream"
+
+Custom Mappings Example 2
+-------------------------
+This example mapping produces the ``gl_buffer_usage`` metric in Prometheus, which provides the current usage state of
+the Graylog ``input``, ``process`` and ``output`` buffers.
+
+Note that three separate mappings are provided to consolidate three independent buffer Graylog metrics into a single
+Prometheus metric with three unique labels (``input``, ``process``, ``output``) that correspond to each Graylog metric.
+
+The ``additional_labels`` property allows for the assignment of an explicit label corresponding to the metric defined in
+the ``match_pattern``.
+
+Mapping Definition::
+
+  - metric_name: "buffer_usage"
+    match_pattern: "org.graylog2.buffers.input.usage"
+    additional_labels:
+      type: "input"
+
+  - metric_name: "buffer_usage"
+    match_pattern: "org.graylog2.buffers.output.usage"
+    additional_labels:
+      type: "output"
+
+  - metric_name: "buffer_usage"
+    match_pattern: "org.graylog2.buffers.process.usage"
+    additional_labels:
+      type: "process"
+
+Custom Mappings Refresh Interval
+--------------------------------
+By default, custom and core mapping files are refreshed (re-read from disk) every 30 seconds. You can override this
+with a custom duration if desired. Use the standard Graylog duration notation (eg ``60s``, ``5m`` or ``1h``).
+
+.. code-block::
+
+    prometheus_exporter_mapping_file_refresh_interval = 5m