I design reliability as a property of the system, not as a reaction to outages. I look at failure modes, redundancy, service degradation and the ability to recover safely, because a resilient system is one that behaves predictably even when some of its components stop working.
SRE, SLI, SLO, SLA, Error Budgets, High Availability, Fault Tolerance, Resilience, Redundancy, Failover, Disaster Recovery, RTO, RPO, Chaos Engineering, Graceful Degradation