A method of provisioning a service in a communication network is described, in which the service comprises at least one virtual network function and at least one virtual network path, which at least one virtual network function and at least one virtual network path are to be implemented in the communication network. The method including obtaining affinity constraints and/or anti-affinity constraints relating to mapping the at least one virtual network path onto the communication network, optionally obtaining affinity constraints and/or anti-affinity constraints relating to mapping the at least one virtual network function onto the communication network, and mapping the at least one virtual network function and at least one virtual network path onto the communication network subject to said constraints.