This paper introduces a scalable decentralized control strategy for the satisfaction of robust stability and robust performance of islanded inverter-interfaced microgrids with the general structure. The proposed control method maintains the stability and the desired performance of the closed-loop system against microgrid topology changes, plug-and-play functionality of DGs, and local load variations. The robust control scheme is formulated in the form of a dynamic output feedback controller for a linear time-invariant system with polytopic-type uncertainty and then converted to an LMI-based convex optimization problem. The capability of the suggested controller is evaluated under several scenarios simulated in MATLAB/SimPowerSystems Toolbox.