Expose an HTTP application externally on IPv4 and IPv6 (ports 80, 8080, 443) with backends in us-west1 and us-east1, global low-latency routing, autoscaling, content-based hostname/path routing, and pass client IPs to backends.

External HTTP(S) Load Balancing is the correct choice because it natively supports IPv4 and IPv6, global low-latency routing, autoscaling, and content-based hostname/path routing via URL maps. It also automatically preserves client IP addresses using the X-Forwarded-For header, which is essential for passing client IPs to backends. Network Load Balancing is a Layer 4 load balancer and doesn't support HTTP/S features like URL maps or global routing. TCP Proxy Load Balancing is also Layer 4 and, while it can use PROXY protocol for client IP, it lacks the HTTP/S specific routing and global features required. Custom headers are not needed for client IP preservation; X-Forwarded-For is standard.