Default Sidekiq routing rules to queue per-worker

What does this MR do?

Due to the incident in gitlab-com/gl-infra/scalability#1991 (closed), in 15.6 (or 15.7) we want to set routing_rules to [['*', nil]] if routing_rules not already set and queue_groups only consists of *s (can be multiple). We don't want to mess up with default routing_rules, when users are touching the queue_groups.

This change will protect users who have customized their queue_groups once we un-revert gitlab!103483 (merged) in 15.7 (or 15.8).

Related issues

• gitlab-com/gl-infra/scalability#1991 (closed)

Manual tests

Test Setup

This MR affects the resulting gitlab.yml. I setup a local Ubuntu 20.04 VM (via multipass) to run some tests. Here's the steps:

• Setup VM

multipass launch lts --mem 8G --disk 20G --cpus 4

• Follow the instruction in the official GitLab download & installation.
• Setup environment to update cookbooks as in https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/master/doc/development/setup.md#get-the-source-of-omnibus-gitlab

Case 1: With default routing rules and default queue_groups

• Content of /etc/gitlab/gitlab.rb

• After sudo gitlab-ctl reconfigure, routing_rules doesn't exist

➜  ~ cat /var/opt/gitlab/gitlab-rails/etc/gitlab.yml | yq '.production.sidekiq.routing_rules'
null

Case 2: With default routing rules and multiple queue_groups all with '*'

➜  ~ cat /var/opt/gitlab/gitlab-rails/etc/gitlab.yml | yq '.production.sidekiq.routing_rules'
null

Case 3: With default routing rules and a queue_group != '*'

➜  ~ cat /var/opt/gitlab/gitlab-rails/etc/gitlab.yml | yq '.production.sidekiq.routing_rules'
- ["*", null]

Case 4: With routing rules set and default queue_groups

➜  ~ cat /var/opt/gitlab/gitlab-rails/etc/gitlab.yml | yq '.production.sidekiq.routing_rules'
- ["urgency=high", "urgent"]
- ["resource_boundary=cpu", "cpu_bound"]
- ["*", "default"]

Case 5: With routing rules set and queue_groups set

➜  ~ cat /var/opt/gitlab/gitlab-rails/etc/gitlab.yml | yq '.production.sidekiq.routing_rules'
- ["urgency=high", "urgent"]
- ["resource_boundary=cpu", "cpu_bound"]
- ["*", "default"]

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened