Which Google Cloud feature should you use to invoke backend services based on a specific HTTP header?

Traffic Director is the appropriate Google Cloud feature for invoking backend services based on specific HTTP headers due to its advanced traffic management capabilities. Traffic Director enables users to define routing rules that direct traffic based on various criteria, including HTTP headers, which can be particularly useful for microservices architectures. This allows for a more granular control of how requests are handled and routed to different backend services depending on their requirements.

In scenarios where service-level routing is necessary—such as directing traffic based on a feature flag or a user’s authentication token—Traffic Director's capabilities allow developers to create policies that examine incoming requests and make routing decisions accordingly. This supports both path-based and header-based routing, enabling efficient and flexible service discovery and traffic management.

Other options, while they have their specific uses in a cloud architecture, do not provide the same level of routing sophistication. For example, Service Directory is primarily focused on service discovery and does not handle traffic management directly based on HTTP headers. Anthos Service Mesh also includes capabilities for routing, but it serves to manage service-to-service communication within a Kubernetes cluster rather than general HTTP traffic management. Internal HTTP(S) Load Balancing is designed for distributing traffic within a Google Cloud Virtual Private Cloud (VPC), and while it does apply routing, it