Reduce queries needed to check if node is a primary or secondary Geo node

If the Geo check for `secondary?` failed, the `RequestStore` cache would always
be set to `false` but the cache would not actually be used due to the semantics
of the ||= operator. This led to dozens of SQL calls with:

```sql
SELECT  1 AS one FROM "geo_nodes" LIMIT 1
```

This commit fixes the caching to handle boolean values properly.

Closes #1644

changelogs/unreleased-ee/sh-fix-geo-node-cache.yml

+---
+title: Reduce queries needed to check if node is a primary or secondary Geo node
+merge_request:
+author:

lib/gitlab/geo.rb

@@ -19,7 +19,7 @@ module Gitlab
     end
 
     def self.enabled?
-      RequestStore.store[:geo_node_enabled] ||= GeoNode.exists?
+      self.cache_boolean(:geo_node_enabled) { GeoNode.exists? }
     end
 
     def self.license_allows?
@@ -27,11 +27,11 @@ module Gitlab
     end
 
     def self.primary?
-      RequestStore.store[:geo_node_primary?] ||= self.enabled? && self.current_node && self.current_node.primary?
+      self.cache_boolean(:geo_node_primary) { self.enabled? && self.current_node && self.current_node.primary? }
     end
 
     def self.secondary?
-      RequestStore.store[:geo_node_secondary] ||= self.enabled? && self.current_node && !self.current_node.primary?
+      self.cache_boolean(:geo_node_secondary) { self.enabled? && self.current_node && !self.current_node.primary? }
     end
 
     def self.geo_node?(host:, port:)
@@ -52,5 +52,14 @@ module Gitlab
       RequestStore.store[:geo_oauth_application] ||=
         Gitlab::Geo.current_node.oauth_application or raise OauthApplicationUndefinedError
     end
+
+    def self.cache_boolean(key, &block)
+      return yield unless RequestStore.active?
+
+      val = RequestStore.store[key]
+      return val unless val.nil?
+
+      RequestStore[key] = yield
+    end
   end
 end

spec/lib/gitlab/geo_spec.rb

@@ -37,6 +37,23 @@ describe Gitlab::Geo, lib: true do
         expect(described_class.enabled?).to be_falsey
       end
     end
+
+    context 'with RequestStore enabled' do
+      before do
+        RequestStore.begin!
+      end
+
+      after do
+        RequestStore.end!
+        RequestStore.clear!
+      end
+
+      it 'return false when no GeoNode exists' do
+        expect(GeoNode).to receive(:exists?).once.and_call_original
+
+        2.times { expect(described_class.enabled?).to be_falsey }
+      end
+    end
   end
 
   describe 'readonly?' do