Update docs

NEWS

@@ -7,6 +7,7 @@ Version 2.9.0
 
 Enhancements and new features:
 
+    * Add a Prometheus export module (issue #930)
     * Port in the -c URI (-c hostname:port) (issue #996)
 
 Bugs corrected:

docs/gw/index.rst

@@ -15,6 +15,7 @@ to providing stats to multiple services (see list below).
    elastic
    influxdb
    opentsdb
+   prometheus
    rabbitmq
    riemann
    statsd

docs/gw/prometheus.rst

@@ -1,34 +1,39 @@
-.. _cassandra:
+.. _prometheus:
 
-Cassandra
-=========
+Prometheus
+==========
 
-You can export statistics to a ``Cassandra`` or ``Scylla`` server.
-The connection should be defined in the Glances configuration file as
-following:
+You can export statistics to a ``Prometheus`` server through an exporter.
+When the *--export-prometheus* is used, Glances creates a Prometheus exporter
+listening on <host:port> (define in the Glances configuration file).
 
 .. code-block:: ini
 
-    [cassandra]
+    [prometheus]
     host=localhost
-    port=9042
-    protocol_version=3
-    keyspace=glances
-    replication_factor=2
-    table=localhost
+    port=9091
+    prefix=glances
 
 and run Glances with:
 
 .. code-block:: console
 
-    $ glances --export-cassandra
+    $ glances --export-prometheus
 
-The data model is the following:
+You can check that Glances exports the stats using this URL: http://localhost:9091
+
+.. image:: ../_static/prometheus_exporter.png
+
+In order to store the metrics in a Prometheus server, you should add this
+exporter to your Prometheus server configuration with the following lines
+(in the prometheus.yml configuration file):
 
 .. code-block:: ini
 
-    CREATE TABLE <table> (plugin text, time timeuuid, stat map<text,float>, PRIMARY KEY (plugin, time))
+    scrape_configs:
+      - job_name: 'glances_exporter'
+        scrape_interval: 5s
+        static_configs:
+          - targets: ['localhost:9091']
 
-Only numerical stats are stored in the Cassandra table. All the stats
-are converted to float. If a stat cannot be converted to float, it is
-not stored in the database.
+.. image:: ../_static/prometheus_server.png

docs/man/glances.1

@@ -1,6 +1,6 @@
 .\" Man page generated from reStructuredText.
 .
-.TH "GLANCES" "1" "Mar 15, 2017" "2.9.0_DEVELOP" "Glances"
+.TH "GLANCES" "1" "Mar 19, 2017" "2.9.0_DEVELOP" "Glances"
 .SH NAME
 glances \- An eye on your system
 .