Configure node-exporter to report correct file system metrics

Without this configuration, all mount points are reporting the same
utilisation metrics [1]. With the rslave option, all root mounts from
the host are visible in the container, so we can remove the bind mounts
for /proc and /sys.

[1] https://github.com/prometheus/node_exporter#docker

Change-Id: I4087dc81f9d1fa5daa24b9df6daf1f9e1ccd702f
Closes-Bug: #1961438

ansible/roles/prometheus/defaults/main.yml

@@ -191,8 +191,7 @@ prometheus_node_exporter_default_volumes:
   - "/etc/localtime:/etc/localtime:ro"
   - "{{ '/etc/timezone:/etc/timezone:ro' if ansible_facts.os_family == 'Debian' else '' }}"
   - "kolla_logs:/var/log/kolla/"
-  - "/proc:/host/proc:ro"
-  - "/sys:/host/sys:ro"
+  - "/:/host:ro,rslave"
 prometheus_memcached_exporter_default_volumes:
   - "{{ node_config_directory }}/prometheus-memcached-exporter/:{{ container_config_directory }}/:ro"
   - "/etc/localtime:/etc/localtime:ro"

ansible/roles/prometheus/templates/prometheus-node-exporter.json.j2

@@ -1,5 +1,5 @@
 {
-    "command": "/opt/node_exporter/node_exporter --path.procfs /host/proc --path.sysfs /host/sys --web.listen-address {{ api_interface_address | put_address_in_context('url') }}:{{ prometheus_node_exporter_port }}{% if prometheus_node_exporter_cmdline_extras %} {{ prometheus_node_exporter_cmdline_extras }}{% endif %}",
+    "command": "/opt/node_exporter/node_exporter --path.procfs /host/proc --path.sysfs /host/sys --path.rootfs /host --web.listen-address {{ api_interface_address | put_address_in_context('url') }}:{{ prometheus_node_exporter_port }}{% if prometheus_node_exporter_cmdline_extras %} {{ prometheus_node_exporter_cmdline_extras }}{% endif %}",
     "config_files": [],
     "permissions": [
         {

releasenotes/notes/node-exporter-filesystem-metrics-d3ae7b0a892d2957.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixes a configuration issue with Node Exporter causing all file system
+    metrics of a host to be identical.
+    `LP#1961438 <https://bugs.launchpad.net/kolla-ansible/+bug/1961438>`__