docs/monitoring: change suggested prometheus port to 9811

Change to 9811 as registered with the prometheus project now.

Closes #444.

config/config_global_test.go

@@ -70,9 +70,9 @@ func TestPrometheusMonitoring(t *testing.T) {
 global:
   monitoring:
     - type: prometheus
-      listen: ':9091'
+      listen: ':9811'
 `)
-	assert.Equal(t, ":9091", conf.Global.Monitoring[0].Ret.(*PrometheusMonitoring).Listen)
+	assert.Equal(t, ":9811", conf.Global.Monitoring[0].Ret.(*PrometheusMonitoring).Listen)
 }
 
 func TestSyslogLoggingOutletFacility(t *testing.T) {

docs/configuration/monitoring.rst

@@ -13,7 +13,7 @@ Prometheus & Grafana
 --------------------
 
 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 ``listen`` attribute is a `net.Listen <https://golang.org/pkg/net/#Listen>`_  string for tcp, e.g. ``:9811`` or ``127.0.0.1:9811`` (port 9811 was reserved to zrepl `on the official list <https://github.com/prometheus/prometheus/wiki/Default-port-allocations/_compare/43e495dd251ee328ac0d08b58084665b5c0f7a7e...459195059b55b414193ebeb80c5ba463d2606951>`_).
 The ``listen_freebind`` attribute is :ref:`explained here <listen-freebind-explanation>`.
 The Prometheus monitoring job appears in the ``zrepl control`` job list and may be specified **at most once**.
 
@@ -30,7 +30,7 @@ The dashboard also contains some advice on which metrics are important to monito
     global:
       monitoring:
         - type: prometheus
-          listen: ':9091'
+          listen: ':9811'
           listen_freebind: true # optional, default false