Log Prometheus current number of host and index

What does this MR do?

1. Log current number of hosts and current index when #initialize is called
2. Log current number of hosts and current index when #next is called
3. Log current number of hosts and current index when #hosts= is called

Issue: https://gitlab.com/gitlab-org/gitlab-ee/issues/13630

CE port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/32044

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

Manual QA

Recording of metrics after a GitLab request:

Screen_Recording_2019-08-22_at_11.31.47_AM

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15440#note_206556427 for how this was tested locally

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

changed milestone to %12.3

added Observability backend backstage [DEPRECATED] database devopsconfigure [DEPRECATED] gitlab.com groupconfigure [DEPRECATED] infradev priority1 workflowin dev + 1 deleted label

added databasereview pending label

	1 Warning
	Reviewer roulette failed to load team data: Failed to read https://about.gitlab.com/roulette.json: 301 Moved Permanently

	1 Message
	This merge request adds or changes files that require a review from the Database team.

This merge request requires a database review. To make sure these changes are reviewed, take the following steps:

1. Ensure the merge request has database and databasereview pending labels. If the merge request modifies database files, Danger will do this for you.
2. Use the Database changes checklist template or add the appropriate items to the MR description.
3. Assign and mention the database reviewer suggested by Reviewer Roulette.

The following files require a review from the Database team:

• ee/lib/gitlab/database/load_balancing/host_list.rb

Reviewer roulette

Changes that require review have been detected! A merge request is normally reviewed by both a reviewer and a maintainer in its primary category (e.g. frontend or backend), and by a maintainer in all other categories.

To spread load more evenly across eligible reviewers, Danger has randomly picked a candidate for each review slot. Feel free to override this selection if you think someone else would be better-suited, or the chosen person is unavailable.

Once you've decided who will review this merge request, mention them as you normally would! Danger does not (yet?) automatically notify them for you.

Category	Reviewer	Maintainer
database	No reviewer available	No maintainer available
backend	No reviewer available	No maintainer available

Generated by Danger

added 1 commit

• eae31acf - Log in Prometheus current number of host and index

Compare with previous version

removed database databasereview pending labels

added database databasereview pending labels

marked the checklist item Changelog entry as completed

@avielle Mind reviewing this MR ?

assigned to @avielle

@tkuah There's documentation at doc/administration/monitoring/prometheus/gitlab_metrics.md that should be updated as we add new metrics. I'm currently updating it for #62514 and there are several missing.

added 2 commits

• 2cf438e1 - Log in Prometheus current number of host and index
• 0d850a7b - Add docs for db_load_balancing metrics

Compare with previous version

marked the checklist item Documentation created/updated or follow-up review issue created as completed

marked the checklist item Separation of EE specific content as completed

marked the checklist item Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process. as completed