An Elastic Wireless Local-Area Network (WLAN) system provides a reliable, flexible, and efficient Internet access to users through installations of heterogeneous access points (APs) including dedicated APs (DAPs), virtual APs (VAPs), and mobile APs (MAPs). The number of APs should be carefully selected to optimize the network performance. Specifically, for heavy traffic, a large number of APs are required. However, the dense deployment of APs introduces the inter-AP interferences which may eventually degrade the communication quality when the number of users are few. In this paper, we propose an active access-point configuration algorithm that activates or deactivates APs according to the changes of network topologies and demands of users for the elastic WLAN system. The algorithm considers the bandwidth difference among heterogeneous AP devices and the total available bandwidth in the network. The number of active APs is minimized to ensure the minimum inter-AP interference subject to the constraints. The host locations can be the candidate positions for the MAPs, because host owners may use them for the Internet access. The effectiveness of the proposed algorithm is demonstrated using the WIMNET simulator.