Fix ProcessObserver to use DB-assigned updated_at timestamps

Reload the process model before passing it to the runner in
ProcessObserver#react_to_state_change and #react_to_instances_change.

Without the reload, the in-memory updated_at value is stale (set before
the DB update). ProcessesSync compares this timestamp against the LRP
annotation to detect drift, causing unnecessary re-syncs when the values
don't match.

Author: philippthun

lib/cloud_controller/process_observer.rb

@@ -37,11 +37,15 @@ def react_to_state_change(process)
 
         process.update(revision: process.app.latest_revision) if process.revisions_enabled?
 
-        @runners.runner_for_process(process).start unless process.needs_staging?
+        # Reload to get the DB-assigned updated_at, which ProcessesSync compares against
+        # the LRP annotation to detect drift. Without this, the stale in-memory value
+        # causes an unnecessary re-sync.
+        @runners.runner_for_process(process.reload).start unless process.needs_staging?
       end
 
       def react_to_instances_change(process)
-        @runners.runner_for_process(process).scale if process.started? && process.active?
+        # Same as above: reload to get the DB-assigned updated_at before building the LRP annotation.
+        @runners.runner_for_process(process.reload).scale if process.started? && process.active?
       end
 
       def with_diego_communication_handling

spec/unit/lib/cloud_controller/process_observer_spec.rb

@@ -5,7 +5,7 @@ module VCAP::CloudController
     let(:stagers) { double(:stagers, stager_for_build: stager) }
     let(:runners) { instance_double(Runners, runner_for_process: runner) }
     let(:stager) { double(:stager) }
-    let(:runner) { instance_double(Diego::Runner, stop: nil, start: nil) }
+    let(:runner) { instance_double(Diego::Runner, stop: nil, start: nil, scale: nil) }
     let(:process_active) { true }
     let(:diego) { false }
     let(:process) do
@@ -33,6 +33,7 @@ module VCAP::CloudController
 
     before do
       ProcessObserver.configure(stagers, runners)
+      allow(process).to receive(:reload).and_return(process)
     end
 
     describe '.deleted' do
@@ -312,6 +313,35 @@ module VCAP::CloudController
           end
         end
       end
+
+      context 'updated_at annotation accuracy' do
+        let(:received) { [] }
+
+        before do
+          allow(runners).to receive(:runner_for_process) do |p|
+            received << p.updated_at
+            runner
+          end
+        end
+
+        context 'when the process instances have changed' do
+          it 'passes a process with the correct updated_at timestamp to the runner', isolation: :truncation do
+            process_model = ProcessModelFactory.make(state: 'STARTED')
+            process_model.update(instances: process_model.instances + 1)
+
+            expect(received.last).to eq(process_model.reload.updated_at)
+          end
+        end
+
+        context 'when the process state has changed' do
+          it 'passes a process with the correct updated_at timestamp to the runner', isolation: :truncation do
+            process_model = ProcessModelFactory.make(state: 'STOPPED')
+            process_model.update(state: ProcessModel::STARTED)
+
+            expect(received.last).to eq(process_model.reload.updated_at)
+          end
+        end
+      end
     end
   end
 end

spec/unit/models/runtime/process_model_spec.rb

@@ -1495,7 +1495,7 @@ def act_as_cf_admin
     end
 
     describe 'saving' do
-      it 'calls AppObserver.updated', isolation: :truncation do
+      it 'calls ProcessObserver.updated', isolation: :truncation do
         process = ProcessModelFactory.make
         expect(ProcessObserver).to receive(:updated).with(process)
         process.update(instances: process.instances + 1)