Don't create duplicate deployments

When the API parameters for a deployment are the same as the last
deployment no new deployment will be created. This prevents duplicate
deployments if nothing changed. As such no hooks will be executed
either, which prevents for example Slack notifications which don't add
value.

app/models/deployment.rb

@@ -353,6 +353,13 @@ class Deployment < ApplicationRecord
     File.join(environment.ref_path, 'deployments', iid.to_s)
   end
 
+  def equal_to?(params)
+    ref == params[:ref] &&
+      tag == params[:tag] &&
+      sha == params[:sha] &&
+      status == params[:status]
+  end
+
   private
 
   def legacy_finished_at

app/services/deployments/create_service.rb

@@ -11,6 +11,8 @@ module Deployments
     end
 
     def execute
+      return last_deployment if last_deployment&.equal_to?(params)
+
       environment.deployments.build(deployment_attributes).tap do |deployment|
         # Deployment#change_status already saves the model, so we only need to
         # call #save ourselves if no status is provided.
@@ -36,5 +38,11 @@ module Deployments
         on_stop: params[:on_stop]
       }
     end
+
+    private
+
+    def last_deployment
+      @environment.last_deployment
+    end
   end
 end

changelogs/unreleased/zj-no-duplicate-deployments.yml

+---
+title: Deployments::CreateService executions are idempotent for duplicate params
+merge_request: 47610
+author:
+type: added

spec/services/deployments/create_service_spec.rb

@@ -41,6 +41,27 @@ RSpec.describe Deployments::CreateService do
 
       expect(service.execute).to be_persisted
     end
+
+    context 'when the last deployment has the same parameters' do
+      let(:params) do
+        {
+          sha: 'b83d6e391c22777fca1ed3012fce84f633d7fed0',
+          ref: 'master',
+          tag: false,
+          status: 'success'
+        }
+      end
+
+      it 'does not create a new deployment' do
+        described_class.new(environment, user, params).execute
+
+        expect(Deployments::UpdateEnvironmentWorker).not_to receive(:perform_async)
+        expect(Deployments::LinkMergeRequestWorker).not_to receive(:perform_async)
+        expect(Deployments::ExecuteHooksWorker).not_to receive(:perform_async)
+
+        described_class.new(environment.reload, user, params).execute
+      end
+    end
   end
 
   describe '#deployment_attributes' do