Today, managing critical infrastructure resilience in smart city is a challenge that can be undertaken by adopting a new class of smart tools, which are able to integrate modeling capability with evidence driven decision support. The Resilience Decision Support tool, as presented in this article, is an innovative and powerful tool that aims at managing critical infrasctructure resilience through a more complex and expressive model based on the Functional Resonance Analysis Method and through the connection of such a model with a system thinking based decision support tool exploiting smart city data. Thanks to ResilienceDS, FRAM model becomes computable and the functional variability that is at the core of the resilience analysis can be quantified. Such quantification allows the decision support tool to compute specific strategies and recommendations for variability dampening at strategic, tactic and operational stage. The solution has been developed in the context of RESOLUTE H2020 project of the European Commission.