The invention discloses network services cloud based network function injection. Disclosed herein are system, method, and computer program product embodiments for providing an API description of an external network service and using the API to integrate the external service into a network. An embodiment operates by receiving, from a service provider, a description of an application programming interface (API), transmitting a call to the service provider using the API for creating a new instance of a service and transmitting to the service provider a traffic flow upon which the service will be applied.