Split off stack-describing pages, to make room for user documentation

docs/source/grafana.rst

 Grafana: Monitoring Dashboards
-========================================
+------------------------------------------
 
 We use `Grafana <https://grafana.com/docs/grafana/latest/introduction/>`_ to visualise the monitoring information through a series of *dashboards*. It allows us to:
 
@@ -8,7 +8,7 @@ We use `Grafana <https://grafana.com/docs/grafana/latest/introduction/>`_ to vis
 * Add *alerts* to trigger on monitoring point formulas reaching a certain treshhold.
 
 Configuration
----------------------------------
+`````````````````````````````````
 
 Grafana comes with preinstalled datasources and dashboards, provided in the ``grafana-central/`` directory. By default, the following datasources are configured:
 
@@ -17,19 +17,19 @@ Grafana comes with preinstalled datasources and dashboards, provided in the ``gr
 * *Grafana API*, providing access to Grafana's API (see f.e. the `Grafana Alerting ReST API <https://editor.swagger.io/?url=https://raw.githubusercontent.com/grafana/grafana/main/pkg/services/ngalert/api/tooling/post.json>`_).
 
 Using Grafana
----------------------------------
+`````````````````````````````````
 
 Go to http://localhost:3001 to access the Grafana instance. The default guest access allows looking at dashboards and inspecting the data in the datasources manually. To create or edit dashboards, or change settings, you need to Sign In. The default credentials are ``admin/admin``.
 
 Adding alerts
----------------------------------
+`````````````````````````````````
 
 We use the `Grafana 8+ alerts <https://grafana.com/docs/grafana/latest/alerting/>`_ to monitor our system. You can add alerts to panels, or add free-floating ones under the ``(alarm bell) -> Alert rules`` menu, which is also used to browse the state of the existing alerts. Some tips:
 
 * Select the *Alert groups* tab to filter alerts or apply custom grouping, for example, by station or by component.
 
 Forwarding alerts to Alerta
----------------------------------
+`````````````````````````````````
 
 The alerts in Grafana come and go, without leaving a track record of ever having been there. To keep track of alerts, we forward them to our Alerta instance. This fowarding has to be configured manually:
 

docs/source/intro.rst

+Introduction
+=====================================
+
+The Operations Central Monitoring setup provides you with the following user services:
+
+* A *Grafana* monitoring & alerting system, exposed on http://localhost:3001,
+* A *Alerta* alarm-management system, exposed on http://localhost:8081.
+
+As well as the following backing services to support the setup:
+
+* A *Prometheus* database that collects monitoring information of the instrument, exposed on http://localhost:9091,
+* A *Node Exporter* scraper that collects monitoring informatino of the host running this software stack, exposed on http://localhost:9100.
+
+.. hint:: The URLs assume you're running this software on localhost. Replace this with the hostname of the hosting system if you're accessing this software on a server.

docs/source/prometheus.rst

 Prometheus: Aggregating Monitoring Data
-========================================
+------------------------------------------
 
 We use `Prometheus <https://prometheus.io/docs/introduction/overview/>`_ to *scrape* monitoring data ("metrics") from across the telescope, and collect it into a single time-series database. Our Prometheus instance is running as the ``prometheus-central`` docker container, which periodically (every 10-60s) obtains metrics from the configured end points. This setup has several advantages:
 
@@ -8,7 +8,7 @@ We use `Prometheus <https://prometheus.io/docs/introduction/overview/>`_ to *scr
 * Widespread support. Many open-source packages already provide a Prometheus metrics end point out of the box.
 
 Configuration
----------------------------------
+`````````````````````````````````
 
 The scraping configuration is provided in ``prometheus-central/prometheus.yml``:
 
@@ -21,7 +21,7 @@ The following end points are scraped:
 * Local machine. Metrics from the machine running our containers is scraped (provided by the ``prometheus-node-exporter`` container).
 
 Inspection in Prometheus
----------------------------------
+`````````````````````````````````
 
 The Prometheus server provides a direct interface on http://localhost:9091 to query the database. PromQL allows you to specify which metric(s) to view, combine, filter, scale, etc. Some general statistics about the scraping process are provided by the following queries::
 
@@ -34,7 +34,7 @@ The Prometheus server provides a direct interface on http://localhost:9091 to qu
 NB: The timestamp(s) for which the data is requested is configured in a side channel. In this interface, it's a time picker defaulting to "now".
 
 Metrics and queries
----------------------------------
+`````````````````````````````````
 
 Prometheus stores each value as an independent metric, identified by a series *name*, string key-value *labels*, and a floar or integer value, for example (see also the `Prometheus Data Model <https://prometheus.io/docs/concepts/data_model/>`_)::
 

docs/source/stack.rst

+Software Stack
+===========================================
+
+The following sections describe how the software stack is setup, how it can be configured, and how to interact with it at a lower level.