ALB Path-Based vs Host-Based Routing

Path-based routing matches on the URL path of an incoming request (e.g. everything under /api/ goes to one target group, everything under /static/ to another), and is the natural fit for a single-domain application split into multiple backend services by function. Host-based routing matches on the Host header instead (e.g. app.example.com routes to one target group, admin.example.com to a completely different one), letting a single ALB serve multiple distinct domains or subdomains, each potentially representing an entirely different application. The two can be combined in the same ALB's rule set — a request is evaluated against all configured rules in priority order, and the first matching rule's action determines routing, with a default catch-all rule handling anything that matches nothing more specific. This flexibility is why a single ALB, correctly configured, can serve an entire company's suite of applications and APIs rather than requiring a separate load balancer per service.