Software bugs and hardware errors are the largest contributors to downtime, and can be permanent (e.g. deterministic memory violations, broken memory modules) or transient (e.g. race conditions, bitflips). Although a large variety of dependability mechanisms exist, only few are used in practice. The existing techniques do not prevail for several reasons: (1) the introduced performance overhead is often not negligible, (2) the gained coverage is not sufficient, and (3) users cannot control and adapt the mechanism. Aaron tackles these challenges by detecting hardware and software errors using automatically diversified software components. It uses these software variants only if CPU spare cycles are present in the system. In this way, Aaron increases fault coverage without incurring a perceivable performance penalty. Our evaluation shows that Aaron provides the same throughput as an execution of the original application while checking a large percentage of requests - whenever load permits.