Two mechanisms exist for configuring load balancing of Fastly services via the API. Directors are bound to a VCL service version, and are a good choice if you want to set up load balancing as part of your version-locked service configuration, but you require more than one director group (if you only need to put all backends under a single director consider the
auto_loadbalance property of a Backend).
Conversely, dynamic server pools are designed to create a load balancing container attached to your service, but with the actual servers defined dynamically. Using a dynamic server pool, servers can be added and removed without creating and activating a new version of the service.