A method (500; 600; 1000; 1100) implemented at a first network function, NF, in a network system, comprising: receiving (502; 601; 1002; 1102), intimacy information of a third NF from the third NF, or receiving intimacy information of a sub-instance of the third NF from the sub-instance of the third NF, wherein the received intimacy information is received via a registration request, and wherein the third NF or the sub-instance of the third NF is a provider of a network service to be registered via the registration request; storing the received intimacy information in the first NF, wherein the received intimacy information comprises at least one of data center information, network topology information and geography location information of the third NF or the sub-instance of the third NF; receiving (502; 602; 1002; 1102), from a second NF, a service discovery request, wherein the service discovery request comprises intimacy information of the second NF, wherein the intimacy information of the second NF comprises at least one of data center information, network topology information and geography location information of the second NF; determining (504; 604; 1004; 1104) information of the intimacy between the second NF and the at least one third NF or the at least one sub-instance of the third NF by at least one of: - physical distance closeness between the second NF and the at least one third NF or the at least one sub-instance of the third NF, - topology closeness between the second NF and the at least one third NF or the at least one sub-instance of the third NF, whether the second NF and the at least one third NF or the at least one sub-instance of the third NF are in a same data center, and - match of one or more of the intimacy information between the second NF and the at least one third NF or the at least one sub-instance of the third NF; and sending (508; 608; 1010; 1110), to the second NF, a service discovery response, wherein the service discovery response comprises the information of the intimacy between the second NF and the at least one third NF or the at least one sub-instance of the third NF to enable the second NF to select one of the at least one third NF or the at least one sub-instance of the third NF as a target NF based on the information of the intimacy. receiving (502; 601; 1002; 1102), intimacy information of a third NF from the third NF, or receiving intimacy information of a sub-instance of the third NF from the sub-instance of the third NF, wherein the received intimacy information is received via a registration request, and wherein the third NF or the sub-instance of the third NF is a provider of a network service to be registered via the registration request; storing the received intimacy information in the first NF, wherein the received intimacy information comprises at least one of data center information, network topology information and geography location information of the third NF or the sub-instance of the third NF; receiving (502; 602; 1002; 1102), from a second NF, a service discovery request, wherein the service discovery request comprises intimacy information of the second NF, wherein the intimacy information of the second NF comprises at least one of data center information, network topology information and geography location information of the second NF; determining (504; 604; 1004; 1104) information of the intimacy between the second NF and the at least one third NF or the at least one sub-instance of the third NF by at least one of: - physical distance closeness between the second NF and the at least one third NF or the at least one sub-instance of the third NF, - topology closeness between the second NF and the at least one third NF or the at least one sub-instance of the third NF, whether the second NF and the at least one third NF or the at least one sub-instance of the third NF are in a same data center, and - match of one or more of the intimacy information between the second NF and the at least one third NF or the at least one sub-instance of the third NF; and - physical distance closeness between the second NF and the at least one third NF or the at least one sub-instance of the third NF, - topology closeness between the second NF and the at least one third NF or the at least one sub-instance of the third NF, whether the second NF and the at least one third NF or the at least one sub-instance of the third NF are in a same data center, and - match of one or more of the intimacy information between the second NF and the at least one third NF or the at least one sub-instance of the third NF; and sending (508; 608; 1010; 1110), to the second NF, a service discovery response, wherein the service discovery response comprises the information of the intimacy between the second NF and the at least one third NF or the at least one sub-instance of the third NF to enable the second NF to select one of the at least one third NF or the at least one sub-instance of the third NF as a target NF based on the information of the intimacy.