Prevent the Geo log cursor from running on primary nodes

changelogs/unreleased-ee/4049-log-cursor-runs-on-primary.yml

+---
+title: Prevent the Geo log cursor from running on primary nodes
+merge_request: 3411
+author:
+type: fixed

lib/gitlab/geo/log_cursor/daemon.rb

@@ -4,6 +4,7 @@ module Gitlab
       class Daemon
         VERSION = '0.2.0'.freeze
         BATCH_SIZE = 250
+        SECONDARY_CHECK_INTERVAL = 1.minute
 
         attr_reader :options
 
@@ -17,6 +18,12 @@ module Gitlab
           trap_signals
 
           until exit?
+            # Prevent the node from processing events unless it's a secondary
+            unless Geo.secondary?
+              sleep(SECONDARY_CHECK_INTERVAL)
+              next
+            end
+
             lease = Lease.try_obtain_with_ttl { run_once! }
 
             return if exit?

spec/ee/support/geo_helpers.rb

@@ -2,7 +2,7 @@ module EE
   module GeoHelpers
     def stub_current_geo_node(node)
       allow(::Gitlab::Geo).to receive(:current_node).and_return(node)
-      allow(node).to receive(:current?).and_return(true)
+      allow(node).to receive(:current?).and_return(true) unless node.nil?
     end
   end
 end

spec/lib/gitlab/geo/log_cursor/daemon_spec.rb

@@ -42,6 +42,26 @@ describe Gitlab::Geo::LogCursor::Daemon, :postgresql, :clean_gitlab_redis_shared
 
       daemon.run!
     end
+
+    it 'skips execution if not a Geo node' do
+      stub_current_geo_node(nil)
+
+      is_expected.to receive(:exit?).and_return(false, true)
+      is_expected.to receive(:sleep).with(1.minute)
+      is_expected.not_to receive(:run_once!)
+
+      daemon.run!
+    end
+
+    it 'skips execution if the current node is a primary' do
+      stub_current_geo_node(primary)
+
+      is_expected.to receive(:exit?).and_return(false, true)
+      is_expected.to receive(:sleep).with(1.minute)
+      is_expected.not_to receive(:run_once!)
+
+      daemon.run!
+    end
   end
 
   describe '#run_once!' do