What does not demonstrate the feature of on-demand self-service in cloud computing?

On-demand self-service in cloud computing allows users to automatically provision and manage computing resources without requiring human interaction with the service provider. This means that users should be able to adjust their cloud resources directly as their needs change, signifying flexibility and control.

Receiving a notification message before server expiration does not exemplify on-demand self-service. While notifications can be an important part of managing resources and ensuring that users are aware of their cloud service status, they do not inherently involve the user taking action to provision or manage those resources. Instead, they serve as passive information that does not involve any execution or control by the user over the service.

In contrast, purchasing a cloud server, upgrading its CPU, and changing the operating system—all represent actions that an end-user can perform directly without needing assistance or intervention from the service provider. These actions demonstrate the capability of on-demand self-service by allowing users to dynamically manage their cloud environment to meet their specific requirements.