Adds option to add extra scrape targets for node exporter

This enables you to scrape external targets more easily.

Change-Id: I55b612d2f5f5a3fc8d21c6d2f71d6c58d89d4e31

ansible/roles/prometheus/defaults/main.yml

@@ -175,6 +175,11 @@ prometheus_mysql_exporter_database_user: "{% if use_preconfigured_databases | bo
 prometheus_active_passive: true
 prometheus_alertmanager_active_passive: true
 
+####################
+# Node Exporter
+####################
+prometheus_node_exporter_targets_extra: []
+
 ####################
 # Blackbox
 ####################

ansible/roles/prometheus/templates/prometheus.yml.j2

@@ -42,6 +42,13 @@ scrape_configs:
           instance: "{{ hostvars[host].prometheus_instance_label }}"
 {% endif %}
 {% endfor %}
+{% for target in prometheus_node_exporter_targets_extra %}
+      - targets:
+        - '{{ target.target }}'
+{% if target.labels | default({}, true) %}
+        labels: {{ target.labels | to_json }}
+{% endif %}
+{% endfor %}
 {% endif %}
 
 {% if enable_prometheus_mysqld_exporter | bool %}

doc/source/reference/logging-and-monitoring/prometheus-guide.rst

@@ -213,3 +213,29 @@ sure to set the ``prometheus_instance_label`` variable to ``None``.
    This feature may generate duplicate metrics temporarily while Prometheus
    updates the metric labels. Please be aware of this while analyzing metrics
    during the transition period.
+
+Exporter configuration
+~~~~~~~~~~~~~~~~~~~~~~
+
+Node Exporter
+-------------
+
+Sometimes it can be useful to monitor hosts outside of the Kolla deployment.
+One method of doing this is to configure a list of additional targets using the
+``prometheus_node_exporter_targets_extra`` variable.  The format of which
+should be a list of dictionaries with the following keys:
+
+* target: URL of node exporter to scrape
+* labels: (Optional) A list of labels to set on the metrics scaped from this
+  exporter.
+
+For example:
+
+.. code-block:: yaml
+  :caption: ``/etc/kolla/globals.yml``
+
+  prometheus_node_exporter_targets_extra:
+    - target: http://10.0.0.1:1234
+      labels:
+        instance: host1
+

releasenotes/notes/adds-node-exporter-targets-extra-c037d4755d1002e8.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Adds ``prometheus_node_exporter_targets_extra`` to add additional scrape
+    targets to the node exporter job. See kolla-ansible-doc:`documentation
+    <reference/logging-and-monitoring/prometheus-guide.html>` for more
+    information.