Enable sidekiq load balancing by default

Changelog: added

doc/administration/database_load_balancing.md

@@ -104,32 +104,19 @@ the following. This balances the load between `host1.example.com` and
 
 1. Save the file and [restart GitLab](restart_gitlab.md#installations-from-source) for the changes to take effect.
 
-### Enable the load balancer for Sidekiq
+### Load balancing for Sidekiq
 
-Sidekiq mostly writes to the database, which means that most of its traffic hits the
-primary database.
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/334494) in GitLab 14.1, load balancing for Sidekick is enabled by default.
 
-Some background jobs can use database replicas to read application state.
+Sidekiq jobs mostly write to the primary database, but there are read-only jobs that can benefit
+from the use of Sidekiq load balancing.
+These jobs can use load balancing and database replicas to read the application state.
 This allows to offload the primary database.
 
-Load balancing is disabled by default in Sidekiq. When enabled, we can define
-[the data consistency](../development/sidekiq_style_guide.md#job-data-consistency-strategies)
+For Sidekiq, we can define
+[data consistency](../development/sidekiq_style_guide.md#job-data-consistency-strategies)
 requirements for a specific job.
 
-To enable it, define the `ENABLE_LOAD_BALANCING_FOR_SIDEKIQ` variable to the environment, as shown below.
-
-For Omnibus installations:
-
-```ruby
-gitlab_rails['env'] = {"ENABLE_LOAD_BALANCING_FOR_SIDEKIQ" => "true"}
-```
-
-For installations from source:
-
-```shell
-export ENABLE_LOAD_BALANCING_FOR_SIDEKIQ="true"
-```
-
 ## Service Discovery
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/5883) in [GitLab Premium](https://about.gitlab.com/pricing/) 11.0.

doc/development/sidekiq_style_guide.md

@@ -478,7 +478,7 @@ of reading a stale record is non-zero due to replicas potentially lagging behind
 
 When the number of jobs that rely on the database increases, ensuring immediate data consistency
 can put unsustainable load on the primary database server. We therefore added the ability to use
-[database load-balancing in Sidekiq workers](../administration/database_load_balancing.md#enable-the-load-balancer-for-sidekiq).
+[database load balancing for Sidekiq workers](../administration/database_load_balancing.md#load-balancing-for-sidekiq).
 By configuring a worker's `data_consistency` field, we can then allow the scheduler to target read replicas
 under several strategies outlined below.
 

lib/gitlab/database/load_balancing.rb

@@ -85,7 +85,6 @@ module Gitlab
       # Returns true if load balancing is to be enabled.
       def self.enable?
         return false if Gitlab::Runtime.rake?
-        return false if Gitlab::Runtime.sidekiq? && !Gitlab::Utils.to_boolean(ENV['ENABLE_LOAD_BALANCING_FOR_SIDEKIQ'], default: false)
         return false unless self.configured?
 
         true

spec/lib/gitlab/database/load_balancing_spec.rb

@@ -142,10 +142,10 @@ RSpec.describe Gitlab::Database::LoadBalancing do
       expect(described_class.enable?).to eq(false)
     end
 
-    it 'returns false when Sidekiq is being used' do
+    it 'returns true when Sidekiq is being used' do
       allow(Gitlab::Runtime).to receive(:sidekiq?).and_return(true)
 
-      expect(described_class.enable?).to eq(false)
+      expect(described_class.enable?).to eq(true)
     end
 
     it 'returns false when running inside a Rake task' do
@@ -170,18 +170,6 @@ RSpec.describe Gitlab::Database::LoadBalancing do
 
       expect(described_class.enable?).to eq(true)
     end
-
-    context 'when ENABLE_LOAD_BALANCING_FOR_SIDEKIQ environment variable is set' do
-      before do
-        stub_env('ENABLE_LOAD_BALANCING_FOR_SIDEKIQ', 'true')
-      end
-
-      it 'returns true when Sidekiq is being used' do
-        allow(Gitlab::Runtime).to receive(:sidekiq?).and_return(true)
-
-        expect(described_class.enable?).to eq(true)
-      end
-    end
   end
 
   describe '.configured?' do