  Resonantly produced sterile neutrinos are considered an attractive dark
matter (DM) candidate only requiring a minimal, well motivated extension to the
standard model of particle physics. With a particle mass restricted to the keV
range, sterile neutrinos are furthermore a prime candidate for warm DM,
characterised by suppressed matter perturbations at the smallest observable
scales. In this paper we take a critical look at the validity of the resonant
scenario in the context of constraints from structure formation. We compare
predicted and observed number of Milky-Way satellites and we introduce a new
method to generalise existing Lyman-$\alpha$ limits based on thermal relic warm
DM to the case of resonant sterile neutrino DM. The tightest limits come from
the Lyman-$\alpha$ analysis, excluding the entire parameter space (at
2-$\sigma$ confidence level) still allowed by X-ray observations. Constraints
from Milky-Way satellite counts are less stringent, leaving room for resonant
sterile neutrino DM most notably around the suggested line signal at 7.1 keV.
