Disable DB writes if node is a GitLab Geo secondary instance

Closes #1185

app/workers/prune_old_events_worker.rb

@@ -3,6 +3,8 @@ class PruneOldEventsWorker
   include CronjobQueue
 
   def perform
+    return if Gitlab::Geo.secondary?
+
     # Contribution calendar shows maximum 12 months of events.
     # Double nested query is used because MySQL doesn't allow DELETE subqueries
     # on the same table.

lib/banzai/renderer.rb

@@ -168,7 +168,7 @@ module Banzai
     end
 
     def update_object(object, html_field, html)
-      object.update_column(html_field, html)
+      object.update_column(html_field, html) unless Gitlab::Geo.secondary?
     end
   end
 end

spec/lib/banzai/renderer_spec.rb

@@ -39,6 +39,13 @@ describe Banzai::Renderer do
         expect_cache_update
         expect(subject).to eq(:html)
       end
+
+      it "skips database caching on a Geo secondary" do
+        allow(Gitlab::Geo).to receive(:secondary?).and_return(true)
+        expect_render
+        expect_cache_update.never
+        expect(subject).to eq(:html)
+      end
     end
 
     context "with a filled cache" do