Merge branch 'alerts-for-built-in-metrics' into 'master'

Import common metrics into database.

Closes gitlab-ee#6948

See merge request gitlab-org/gitlab-ce!21459

3 files changed, 49 insertions, 6 deletions

diff --git a/doc/development/README.md b/doc/development/README.md
index 20f8fa1d368..e786d6594c7 100644
--- a/doc/development/README.md
+++ b/doc/development/README.md
@@ -47,6 +47,7 @@ description: 'Learn how to contribute to GitLab.'
 - [How to dump production data to staging](db_dump.md)
 - [Working with the GitHub importer](github_importer.md)
 - [Working with Merge Request diffs](diffs.md)
+- [Prometheus metrics](prometheus_metrics.md)
 
 ## Performance guides
 
diff --git a/doc/development/prometheus_metrics.md b/doc/development/prometheus_metrics.md
new file mode 100644
index 00000000000..b6b6d9665ea
--- /dev/null
+++ b/doc/development/prometheus_metrics.md
@@ -0,0 +1,48 @@
+# Working with Prometheus Metrics
+
+## Adding to the library
+
+We strive to support the 2-4 most important metrics for each common system service that supports Prometheus. If you are looking for support for a particular exporter which has not yet been added to the library, additions can be made [to the `common_metrics.yml`](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/prometheus/common_metrics.yml) file.
+
+### Query identifier
+
+The requirement for adding a new metric is to make each query to have an unique identifier which is used to update the metric later when changed:
+
+```yaml
+- group: Response metrics (NGINX Ingress)
+  metrics:
+  - title: "Throughput"
+    y_label: "Requests / Sec"
+    queries:
+    - id: response_metrics_nginx_ingress_throughput_status_code
+      query_range: 'sum(rate(nginx_upstream_responses_total{upstream=~"%{kube_namespace}-%{ci_environment_slug}-.*"}[2m])) by (status_code)'
+      unit: req / sec
+      label: Status Code
+```
+
+### Update existing metrics
+
+After you add or change existing _common_ metric you have to create a new database migration that will query and update all existing metrics.
+
+NOTE: **Note:**
+If a query metric (which is identified by `id:`) is removed it will not be removed from database by default.
+You might want to add additional database migration that makes a decision what to do with removed one.
+For example: you might be interested in migrating all dependent data to a different metric.
+
+```ruby
+class ImportCommonMetrics < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  require Rails.root.join('db/importers/common_metrics_importer.rb')
+
+  DOWNTIME = false
+
+  def up
+    Importers::CommonMetricsImporter.new.execute
+  end
+
+  def down
+    # no-op
+  end
+end
+```
diff --git a/doc/user/project/integrations/prometheus_library/metrics.md b/doc/user/project/integrations/prometheus_library/metrics.md
index 96a22316265..ec16902fcc8 100644
--- a/doc/user/project/integrations/prometheus_library/metrics.md
+++ b/doc/user/project/integrations/prometheus_library/metrics.md
@@ -17,9 +17,3 @@ GitLab retrieves performance data from the configured Prometheus server, and att
 
 In order to isolate and only display relevant metrics for a given environment, GitLab needs a method to detect which labels are associated. To do that,
 GitLab uses the defined queries and fills in the environment specific variables. Typically this involves looking for the [$CI_ENVIRONMENT_SLUG](../../../../ci/variables/README.md#predefined-variables-environment-variables), but may also include other information such as the project's Kubernetes namespace. Each search query is defined in the [exporter specific documentation](#prometheus-metrics-library).
-
-## Adding to the library
-
-We strive to support the 2-4 most important metrics for each common system service that supports Prometheus. If you are looking for support for a particular exporter which has not yet been added to the library, additions can be made [to the `additional_metrics.yml`](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/prometheus/additional_metrics.yml) file.
-
-> Note: The library is only for monitoring public, common, system services which all customers can benefit from. Support for monitoring [customer proprietary metrics](https://gitlab.com/gitlab-org/gitlab-ee/issues/2273) will be added in a subsequent release.