You need to invoke backend implementations selected by an HTTP header; backends run in managed instance groups across regions and should be loosely coupled. Which Google Cloud feature should you use?

Traffic Director is the correct choice because it provides global load balancing and advanced traffic management for microservices, including content-based routing (like routing based on HTTP headers) to backend services across multiple regions. It acts as a fully managed control plane for the open-source Istio service mesh, enabling fine-grained control over traffic flow to managed instance groups. Service Directory is incorrect because it's primarily a service discovery and registration platform, not a traffic management solution for routing based on HTTP headers. Anthos Service Mesh is incorrect because while it offers similar capabilities to Traffic Director, Traffic Director is the fully managed Google Cloud solution specifically designed for this global, header-based routing use case without requiring a full Anthos deployment. Internal HTTP(S) Load Balancing is incorrect because it's a regional load balancer and doesn't support global traffic management across regions for this specific scenario.