Fix pipeline schedule edge case

If pipeline schedule is to run at the exact same time with when cron
worker runs, the pipeline schedule will not be executed at the
ideal timing.

We fix this bug by comparing the exact matching of ideal and
cron worker's next run at.

app/models/ci/pipeline_schedule.rb

@@ -55,15 +55,20 @@ module Ci
     # This way, a schedule like `*/1 * * * *` won't be triggered in a short interval
     # when PipelineScheduleWorker runs irregularly by Sidekiq Memory Killer.
     def set_next_run_at
-      self.next_run_at = Gitlab::Ci::CronParser.new(Settings.cron_jobs['pipeline_schedule_worker']['cron'],
-                                                    Time.zone.name)
-                                               .next_time_from(ideal_next_run_at)
+      now = Time.zone.now
+      ideal_next_run = ideal_next_run_from(now)
+
+      self.next_run_at = if ideal_next_run == cron_worker_next_run_from(now)
+                           ideal_next_run
+                         else
+                           cron_worker_next_run_from(ideal_next_run)
+                         end
     end
 
     def schedule_next_run!
       save! # with set_next_run_at
     rescue ActiveRecord::RecordInvalid
-      update_attribute(:next_run_at, nil) # update without validation
+      update_column(:next_run_at, nil) # update without validation
     end
 
     def job_variables
@@ -72,9 +77,15 @@ module Ci
 
     private
 
-    def ideal_next_run_at
+    def ideal_next_run_from(start_time)
       Gitlab::Ci::CronParser.new(cron, cron_timezone)
-        .next_time_from(Time.zone.now)
+                            .next_time_from(start_time)
+    end
+
+    def cron_worker_next_run_from(start_time)
+      Gitlab::Ci::CronParser.new(Settings.cron_jobs['pipeline_schedule_worker']['cron'],
+                                Time.zone.name)
+                            .next_time_from(start_time)
     end
   end
 end

changelogs/unreleased/fix-pipeline-schedule-edge-case.yml

+---
+title: Fix pipeline schedule does not run correctly when it's scheduled at the same
+  time with the cron worker
+merge_request: 29848
+author:
+type: fixed

spec/models/ci/pipeline_schedule_spec.rb

@@ -88,23 +88,8 @@ describe Ci::PipelineSchedule do
 
   describe '#set_next_run_at' do
     let(:pipeline_schedule) { create(:ci_pipeline_schedule, :nightly) }
-    let(:ideal_next_run_at) { pipeline_schedule.send(:ideal_next_run_at) }
-
-    let(:expected_next_run_at) do
-      Gitlab::Ci::CronParser.new(Settings.cron_jobs['pipeline_schedule_worker']['cron'], Time.zone.name)
-        .next_time_from(ideal_next_run_at)
-    end
-
-    let(:cron_worker_next_run_at) do
-      Gitlab::Ci::CronParser.new(Settings.cron_jobs['pipeline_schedule_worker']['cron'], Time.zone.name)
-        .next_time_from(Time.zone.now)
-    end
-
-    context 'when creates new pipeline schedule' do
-      it 'updates next_run_at automatically' do
-        expect(pipeline_schedule.next_run_at).to eq(expected_next_run_at)
-      end
-    end
+    let(:ideal_next_run_at) { pipeline_schedule.send(:ideal_next_run_from, Time.zone.now) }
+    let(:cron_worker_next_run_at) { pipeline_schedule.send(:cron_worker_next_run_from, Time.zone.now) }
 
     context 'when PipelineScheduleWorker runs at a specific interval' do
       before do
@@ -129,7 +114,7 @@ describe Ci::PipelineSchedule do
       let(:pipeline_schedule) { create(:ci_pipeline_schedule, :every_minute) }
 
       it "updates next_run_at to the sidekiq worker's execution time" do
-        Timecop.freeze(2019, 06, 19, 12, 00) do
+        Timecop.freeze(Time.parse("2019-06-01 12:18:00+0000")) do
           expect(pipeline_schedule.next_run_at).to eq(cron_worker_next_run_at)
         end
       end
@@ -157,9 +142,8 @@ describe Ci::PipelineSchedule do
       let(:new_cron) { '0 0 1 1 *' }
 
       it 'updates next_run_at automatically' do
-        pipeline_schedule.update!(cron: new_cron)
-
-        expect(pipeline_schedule.next_run_at).to eq(expected_next_run_at)
+        expect { pipeline_schedule.update!(cron: new_cron) }
+          .to change { pipeline_schedule.next_run_at }
       end
     end
   end
@@ -167,21 +151,24 @@ describe Ci::PipelineSchedule do
   describe '#schedule_next_run!' do
     let!(:pipeline_schedule) { create(:ci_pipeline_schedule, :nightly) }
 
-    context 'when reschedules after 10 days from now' do
-      let(:future_time) { 10.days.from_now }
-      let(:ideal_next_run_at) { pipeline_schedule.send(:ideal_next_run_at) }
+    before do
+      pipeline_schedule.update_column(:next_run_at, nil)
+    end
 
-      let(:expected_next_run_at) do
-        Gitlab::Ci::CronParser.new(Settings.cron_jobs['pipeline_schedule_worker']['cron'], Time.zone.name)
-          .next_time_from(ideal_next_run_at)
+    it 'updates next_run_at' do
+      expect { pipeline_schedule.schedule_next_run! }
+        .to change { pipeline_schedule.next_run_at }
+    end
+
+    context 'when record is invalid' do
+      before do
+        allow(pipeline_schedule).to receive(:save!) { raise ActiveRecord::RecordInvalid.new(pipeline_schedule) }
       end
 
-      it 'points to proper next_run_at' do
-        Timecop.freeze(future_time) do
-          pipeline_schedule.schedule_next_run!
+      it 'nullifies the next run at' do
+        pipeline_schedule.schedule_next_run!
 
-          expect(pipeline_schedule.next_run_at).to eq(expected_next_run_at)
-        end
+        expect(pipeline_schedule.next_run_at).to be_nil
       end
     end
   end