[#1444] Passing parent trace from web to sidekiq

lib/elastic_apm/spies/sidekiq.rb

@@ -30,7 +30,13 @@ class SidekiqSpy
       class Middleware
         def call(_worker, job, queue)
           name = SidekiqSpy.name_for(job)
-          transaction = ElasticAPM.start_transaction(name, 'Sidekiq')
+          transaction = if job['trace_id']
+            ElasticAPM.start_transaction(name, 'Sidekiq', trace_context: ElasticAPM::TraceContext.new(
+              traceparent: ElasticAPM::TraceContext::Traceparent.new(trace_id: job['trace_id'])
+            ))
+          else
+            ElasticAPM.start_transaction(name, 'Sidekiq')
+          end
           ElasticAPM.set_label(:queue, queue)
 
           yield
@@ -47,6 +53,14 @@ def call(_worker, job, queue)
         end
       end
 
+      class ParentTraceMiddleware
+        def call(job_class_or_string, job, queue, redis_pool)
+          job.merge!(
+            'trace_id' => ElasticAPM.current_transaction&.trace_id
+          )
+        end
+      end
+
       def self.name_for(job)
         klass = job['class']
 
@@ -64,6 +78,12 @@ def install_middleware
             chain.add Middleware
           end
         end
+
+        Sidekiq.configure_client do |config|
+          config.client_middleware do |chain|
+             chain.add ParentTraceMiddleware
+          end
+        end
       end
 
       # @api private

spec/elastic_apm/spies/sidekiq_spec.rb

@@ -105,6 +105,60 @@ def perform
         expect(transaction['outcome']).to eq 'success'
       end
 
+      it 'creates child transaction when trace_id is present in job' do
+        with_agent do
+          parent_trace_id = 'abc123def456'
+
+          # Simulate a job with trace_id from parent
+          job_with_trace = {
+            'class' => 'ElasticAPM::HardWorker',
+            'trace_id' => parent_trace_id,
+            'args' => []
+          }
+
+          middleware = Spies::SidekiqSpy::Middleware.new
+          worker = HardWorker.new
+
+          middleware.call(worker, job_with_trace, 'default') do
+            worker.perform
+          end
+        end
+
+        wait_for transactions: 1
+
+        transaction, = @mock_intake.transactions
+        expect(transaction).to_not be_nil
+        expect(transaction['name']).to eq 'ElasticAPM::HardWorker'
+        expect(transaction['type']).to eq 'Sidekiq'
+        expect(transaction['trace_id']).to eq('abc123def456')
+      end
+
+      it 'creates independent transaction when no trace_id is present' do
+        with_agent do
+          # Simulate a job without trace_id
+          job_without_trace = {
+            'class' => 'ElasticAPM::HardWorker',
+            'args' => []
+          }
+
+          middleware = Spies::SidekiqSpy::Middleware.new
+          worker = HardWorker.new
+
+          middleware.call(worker, job_without_trace, 'default') do
+            worker.perform
+          end
+        end
+
+        wait_for transactions: 1
+
+        transaction, = @mock_intake.transactions
+        expect(transaction).to_not be_nil
+        expect(transaction['name']).to eq 'ElasticAPM::HardWorker'
+        expect(transaction['type']).to eq 'Sidekiq'
+        # Should have its own trace_id since no parent was provided
+        expect(transaction['trace_id']).to_not be_nil
+      end
+
       it 'reports errors' do
         with_agent do
           Sidekiq::Testing.inline! do