Remove UnicornCheck service

Drops UnicornCheck.
Split from https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61888.

Changelog: removed

changelogs/unreleased/330402-remove-unicorn-gitlab-health-check.yml

+---
+title: Remove UnicornCheck service
+merge_request: 62204
+author:
+type: removed

lib/gitlab/health_checks/unicorn_check.rb

-# frozen_string_literal: true
-
-module Gitlab
-  module HealthChecks
-    # This check can only be run on Unicorn `master` process
-    class UnicornCheck
-      extend SimpleAbstractCheck
-
-      class << self
-        include Gitlab::Utils::StrongMemoize
-
-        private
-
-        def metric_prefix
-          'unicorn_check'
-        end
-
-        def successful?(result)
-          result > 0
-        end
-
-        def check
-          return unless http_servers
-
-          http_servers.sum(&:worker_processes)
-        end
-
-        # Traversal of ObjectSpace is expensive, on fully loaded application
-        # it takes around 80ms. The instances of HttpServers are not a subject
-        # to change so we can cache the list of servers.
-        def http_servers
-          strong_memoize(:http_servers) do
-            next unless Gitlab::Runtime.unicorn?
-
-            ObjectSpace.each_object(::Unicorn::HttpServer).to_a
-          end
-        end
-      end
-    end
-  end
-end

lib/gitlab/metrics/exporter/web_exporter.rb

@@ -30,8 +30,7 @@ module Gitlab
           # application: https://gitlab.com/gitlab-org/gitlab/issues/35343
           self.readiness_checks = [
             WebExporter::ExporterCheck.new(self),
-            Gitlab::HealthChecks::PumaCheck,
-            Gitlab::HealthChecks::UnicornCheck
+            Gitlab::HealthChecks::PumaCheck
           ]
         end
 

spec/lib/gitlab/health_checks/unicorn_check_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-
-RSpec.describe Gitlab::HealthChecks::UnicornCheck do
-  let(:result_class) { Gitlab::HealthChecks::Result }
-  let(:readiness) { described_class.readiness }
-  let(:metrics) { described_class.metrics }
-
-  before do
-    described_class.clear_memoization(:http_servers)
-  end
-
-  shared_examples 'with state' do |(state, message)|
-    it "does provide readiness" do
-      expect(readiness).to eq(result_class.new('unicorn_check', state, message))
-    end
-
-    it "does provide metrics" do
-      expect(metrics).to include(
-        an_object_having_attributes(name: 'unicorn_check_success', value: state ? 1 : 0))
-      expect(metrics).to include(
-        an_object_having_attributes(name: 'unicorn_check_latency_seconds', value: be >= 0))
-    end
-  end
-
-  context 'when Unicorn is not loaded' do
-    before do
-      allow(Gitlab::Runtime).to receive(:unicorn?).and_return(false)
-      hide_const('Unicorn')
-    end
-
-    it "does not provide readiness and metrics" do
-      expect(readiness).to be_nil
-      expect(metrics).to be_nil
-    end
-  end
-
-  context 'when Unicorn is loaded' do
-    let(:http_server_class) { Struct.new(:worker_processes) }
-
-    before do
-      allow(Gitlab::Runtime).to receive(:unicorn?).and_return(true)
-      stub_const('Unicorn::HttpServer', http_server_class)
-    end
-
-    context 'when no servers are running' do
-      it_behaves_like 'with state', [false, 'unexpected Unicorn check result: 0']
-    end
-
-    context 'when servers without workers are running' do
-      before do
-        http_server_class.new(0)
-      end
-
-      it_behaves_like 'with state', [false, 'unexpected Unicorn check result: 0']
-    end
-
-    context 'when servers with workers are running' do
-      before do
-        http_server_class.new(1)
-      end
-
-      it_behaves_like 'with state', true
-    end
-  end
-end