daemon: expose prometheus in new global.monitoring config section + document it

refs #67

docs/changelog.rst

@@ -10,6 +10,11 @@ Changelog
 The changelog summarized bugfixes that are deemed relevant for users.
 Developers should consult the git commit log or GitHub issue tracker.
 
+0.0.4 (unreleased)
+------------------
+
+* |feature| :issue:`67`: Expose `Prometheus <https://prometheus.io>`_ metrics via HTTP (:ref:`config docs <monitoring-prometheus>`)
+
 0.0.3
 -----
 

docs/configuration.rst

@@ -13,4 +13,5 @@ Configuration
     configuration/map_filter_syntax
     configuration/prune
     configuration/logging
+    configuration/monitoring
     configuration/misc

docs/configuration/logging.rst

@@ -8,7 +8,7 @@ Logging
 zrepl uses structured logging to provide users with easily processable log messages.
 
 Logging outlets are configured in the ``global`` section of the |mainconfig|.
-Check out :sampleconf:`random/logging.yml` for an example on how to configure multiple outlets:
+Check out :sampleconf:`random/logging_and_monitoring.yml` for an example on how to configure multiple outlets:
 
 ::
 

docs/configuration/monitoring.rst

@@ -0,0 +1,30 @@
+.. include:: ../global.rst.inc
+
+.. _monitoring:
+
+Monitoring
+==========
+
+Monitoring endpoints are configured in the ``global.monitoring`` section of the |mainconfig|.
+Check out :sampleconf:`random/logging_and_monitoring.yml` for examples.
+
+.. _monitoring-prometheus:
+
+Prometheus
+----------
+
+zrepl can expose `Prometheus metrics <https://prometheus.io/docs/instrumenting/exposition_formats/>`_ via HTTP.
+The ``listen`` attribute is a `net.Listen <https://golang.org/pkg/net/#Listen>`_  string for tcp, e.g. ``:9091`` or ``127.0.0.1:9091``.
+
+The Prometheues monitoring job appears in the ``zrepl control`` job list and may be specified **at most once**.
+There is no stability guarantee on the exported metrics.
+
+::
+
+    global:
+      monitoring:
+        - type: prometheus
+          listen: ':9091'
+
+
+

docs/tutorial.rst

@@ -193,6 +193,7 @@ Summary
 Congratulations, you have a working pull backup. Where to go next?
 
 * Read more about :ref:`configuration format, options & job types <configuration_toc>`
+* Configure :ref:`logging <logging>` \& :ref:`monitoring <monitoring>`.
 * Learn about :ref:`implementation details <implementation_toc>` of zrepl.
 
 

docs/usage.rst

@@ -37,7 +37,7 @@ zrepl daemon
 ============
 
 All actual work zrepl does is performed by a daemon process.
-Logging is configurable via the config file. Please refer to the :ref:`logging documention <logging>`.
+The daemon supports structured :ref:`logging <logging>` and provides :ref:`monitoring endpoints <monitoring>`.
 
 When installating from a package, the package maintainer should have provided an init script / systemd.service file.
 You should thus be able to start zrepl daemon using your init system.