A server migration service (SMS) has been proposed as a means of improving communication QoS of network application (NW-Apps) operated on Infrastructure as a Service (IaaS)-type cloud services. In SMS, computers called workplaces (WPs) are distributed across the network, and a server-side application (server) of a NW-App can migrate among the WPs in order to improve the communication QoS of NW-Apps. In this paper, we tackle a WP capacity design problem where we determine where WPs should be placed within a NW, and what capacity they should have. We propose two methods for the problem. Method 1 seeks to place higher capacity WPs at locations where more servers are likely to stay. Method 2 tries to position WPs such that the required level of communication QoS for NW-Apps can be satisfied with at least one WP at any location in the NW. This is accomplished by formulating the WP capacity design problem as a minimum dominating set (MDS) problem and solving it.