1. A computer-implemented method for implementing network-related services, comprising: establishing, by a computer system of a computing resource provider, a direct physical connection with at least one customer entity by which the computing resource provider is configured to provide the customer entity with access to at least one network, the direct physical connection comprising a communication link between the at least one customer entity and the computing resource provider; receiving, by the computer system of the computing resource provider, over a second network connection, instructions from at least one third-party entity for implementing at least one network-related service to operate on network traffic received through at least one network gateway on behalf of a customer entity, the network gateway controlling access to the at least one network, the at least one third-party entity being a separate entity from the computing resource provider, the customer entity distinct from the third-party entity, the at least one network-related service including at least one of a distributed denial of service (DDoS) mitigation service, an unsolicited message control service, a data firewalling service, or a data encryption service; providing an interface that enables the customer entity to select the at least one network-related service corresponding to the received instructions; provisioning, by the computer system of the computing resource provider, the at least one network-related service in a separate virtual computer system instance that is accessible by the at least one customer entity via the direct physical connection; and configuring the at least one network gateway to route the network traffic between the customer entity and a public communications network through the separate virtual computer system instance, the network traffic of the direct physical connection being subjected to the at least one network-related service, and the computing resource provider controlling network traffic over the direct physical connection such that the computer system is operable to adjust at least one capability relating to an operation of the at least one network gateway in response to a change to a demand of the at least one of the network gateway.