Merge branch 'prometheus-external-labels-configuration' into 'master'

Allow `external_labels` to be configured

See merge request gitlab-org/omnibus-gitlab!4494

changelogs/unreleased/prometheus-external-labels-configuration.yml

+---
+title: Allow Prometheus external_labels to be configured
+merge_request: 4494
+author: Chris Weyl @rsrchboy
+type: changed

doc/settings/prometheus.md

@@ -51,6 +51,19 @@ Custom list:
 prometheus['rules_files'] = ['/path/to/rules/*.rules', '/path/to/single/file.rules']
 ```
+## External labels
+
+To set [external labels](https://prometheus.io/docs/prometheus/latest/configuration/configuration/):
+
+```ruby
+prometheus['external_labels'] = {
+    'region' => 'us-west-2',
+    'source' => 'omnibus',
+}
+```
+
+No external labels are set by default.
+
 ## node_exporter
 The node_exporter provides system level metrics.

files/gitlab-config-template/gitlab.rb.template

@@ -1638,6 +1638,7 @@ gitlab_rails['object_store']['objects']['terraform_state']['bucket'] = nil
 # prometheus['rules_files'] = ['/var/opt/gitlab/prometheus/rules/*.rules']
 # prometheus['scrape_interval'] = 15
 # prometheus['scrape_timeout'] = 15
+# prometheus['external_labels'] = { }
 # prometheus['env_directory'] = '/opt/gitlab/etc/prometheus/env'
 # prometheus['env'] = {
 #   'SSL_CERT_DIR' => "/opt/gitlab/embedded/ssl/certs/"

files/gitlab-cookbooks/monitoring/attributes/default.rb

@@ -21,6 +21,7 @@ default['monitoring']['prometheus']['rules_directory'] = "/var/opt/gitlab/promet
 default['monitoring']['prometheus']['scrape_interval'] = 15
 default['monitoring']['prometheus']['scrape_timeout'] = 15
 default['monitoring']['prometheus']['scrape_configs'] = []
+default['monitoring']['prometheus']['external_labels'] = {}
 default['monitoring']['prometheus']['listen_address'] = 'localhost:9090'
 default['monitoring']['prometheus']['alertmanagers'] = nil

files/gitlab-cookbooks/monitoring/recipes/prometheus.rb

@@ -57,6 +57,7 @@ configuration = Prometheus.hash_to_yaml({
                                           'global' => {
                                             'scrape_interval' => "#{node['monitoring']['prometheus']['scrape_interval']}s",
                                             'scrape_timeout' => "#{node['monitoring']['prometheus']['scrape_timeout']}s",
+                                            'external_labels' => node['monitoring']['prometheus']['external_labels'],
                                           },
                                           'remote_read' => node['monitoring']['prometheus']['remote_read'],
                                           'remote_write' => node['monitoring']['prometheus']['remote_write'],

spec/chef/monitoring/prometheus_spec.rb

@@ -5,6 +5,7 @@ prometheus_yml_output = <<-PROMYML
   global:
     scrape_interval: 15s
     scrape_timeout: 15s
+    external_labels: {}
   remote_read: []
   remote_write: []
   rule_files: