Which AWS service provides configuration management services that can be used as a lifecycle tool, and allows for an entire application's architecture to be defined?

AWS OpsWorks is the correct answer because it is primarily designed for configuration management and enables users to define the entire application's architecture through a lifecycle management framework. OpsWorks allows you to manage applications with Chef and Puppet, which provides the capability to describe the system configuration as code. This means you can automate the deployment, configuration, and management of your applications in a consistent and repeatable manner.

In contrast, AWS CloudFormation, although it also allows for infrastructure as code, primarily focuses on creating and managing the underlying AWS resources rather than offering direct configuration management for applications in the same way OpsWorks does. AWS CodeDeploy is a deployment service that automates code deployments to various compute services but does not provide comprehensive configuration management. Lastly, AWS EC2 is a compute service that allows the provisioning of virtual servers but lacks intrinsic capabilities for lifecycle management and configuration management in the context of an application's architecture. Therefore, OpsWorks is uniquely suited for managing application lifecycles with a focus on configuration, making it the right choice for this question.