Your company is developing a new application that will allow globally distributed users to upload pictures and share them with other selected users. The application will support millions of concurrent users. You want to allow developers to focus on just building code without having to create and maintain the underlying infrastructure. Which service should you use to deploy the application?

App Engine is the correct choice because it is a fully managed, serverless platform that allows developers to deploy applications without managing the underlying infrastructure. This aligns perfectly with the requirement to "focus on just building code." It also scales automatically to handle millions of concurrent users and is well-suited for globally distributed applications. Cloud Endpoints is incorrect because it is an API management tool, not a platform for deploying entire applications. Compute Engine is incorrect as it provides Infrastructure as a Service (IaaS), requiring users to manage virtual machines, which contradicts the goal of avoiding infrastructure maintenance. Google Kubernetes Engine (GKE) is incorrect because while it offers powerful container orchestration, it still requires more operational overhead and infrastructure management than App Engine, which is a Platform as a Service (PaaS).