feat(lambda): read cloud.account.id from symlink in Lambda detector

instrumentation/aws_lambda/CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release History: opentelemetry-instrumentation-aws_lambda
 
+### Unreleased
+
+* ADDED: Read `cloud.account.id` from symlink created by the OTel Lambda Extension
+
 ### v0.6.0 / 2025-10-22
 
 * BREAKING CHANGE: Min Ruby Version 3.2

resources/aws/lib/opentelemetry/resource/detector/aws/lambda.rb

@@ -17,6 +17,9 @@ module Lambda
           # Create a constant for resource semantic conventions
           RESOURCE = OpenTelemetry::SemanticConventions::Resource
 
+          # Path to the symlink created by the OTel Lambda extension containing the AWS account ID
+          ACCOUNT_ID_SYMLINK_PATH = '/tmp/.otel-account-id'
+
           def detect
             # Return empty resource if not running on Lambda
             return OpenTelemetry::SDK::Resources::Resource.create({}) unless lambda_environment?
@@ -34,6 +37,14 @@ def detect
 
               # Convert memory size to integer
               resource_attributes[RESOURCE::FAAS_MAX_MEMORY] = ENV['AWS_LAMBDA_FUNCTION_MEMORY_SIZE'].to_i if ENV['AWS_LAMBDA_FUNCTION_MEMORY_SIZE']
+
+              # Read cloud.account.id from symlink created by the OTel Lambda extension
+              begin
+                account_id = File.readlink(ACCOUNT_ID_SYMLINK_PATH)
+                resource_attributes[RESOURCE::CLOUD_ACCOUNT_ID] = account_id
+              rescue Errno::ENOENT, Errno::EINVAL
+                # Symlink doesn't exist or is not a symlink — silently skip
+              end
             rescue StandardError => e
               OpenTelemetry.handle_error(exception: e, message: 'Lambda resource detection failed')
               return OpenTelemetry::SDK::Resources::Resource.create({})

resources/aws/test/opentelemetry/resource/detector/aws/lambda_test.rb

@@ -61,6 +61,40 @@
 
         _(attributes).wont_include(OpenTelemetry::SemanticConventions::Resource::FAAS_MAX_MEMORY)
       end
+
+      describe 'cloud.account.id from symlink' do
+        it 'reads cloud.account.id from the symlink' do
+          File.stub :readlink, '123456789012' do
+            resource = detector.detect
+            attributes = resource.attribute_enumerator.to_h
+            _(attributes[OpenTelemetry::SemanticConventions::Resource::CLOUD_ACCOUNT_ID]).must_equal('123456789012')
+          end
+        end
+
+        it 'preserves leading zeros in account id' do
+          File.stub :readlink, '000123456789' do
+            resource = detector.detect
+            attributes = resource.attribute_enumerator.to_h
+            _(attributes[OpenTelemetry::SemanticConventions::Resource::CLOUD_ACCOUNT_ID]).must_equal('000123456789')
+          end
+        end
+
+        it 'silently skips when symlink does not exist' do
+          File.stub :readlink, ->(_path) { raise Errno::ENOENT } do
+            resource = detector.detect
+            attributes = resource.attribute_enumerator.to_h
+            _(attributes).wont_include(OpenTelemetry::SemanticConventions::Resource::CLOUD_ACCOUNT_ID)
+          end
+        end
+
+        it 'silently skips when path is not a symlink' do
+          File.stub :readlink, ->(_path) { raise Errno::EINVAL } do
+            resource = detector.detect
+            attributes = resource.attribute_enumerator.to_h
+            _(attributes).wont_include(OpenTelemetry::SemanticConventions::Resource::CLOUD_ACCOUNT_ID)
+          end
+        end
+      end
     end
 
     describe 'when partial Lambda environment is detected' do