Sophie, a cloud architect, leverages container technology to deploy applications along with their dependencies, encompassing libraries, configuration files, binaries, and other resources. These containers operate independently from other processes within the cloud environment. Sophie adheres to the five-tier container technology architecture for the containerization of applications. Currently, she is engaged in verifying and validating image contents, signing images, and transmitting them to the registries. Which of the following tiers of the container technology architecture is Sophie currently operating in?