⚠ Glossary
Reliability glossary, in plain English
Plain-English definitions of the terms you will hear around SRE, resilience testing and chaos engineering: blast radius, RTO, RPO, steady state, GameDay and more.
Terms
+ SLI (service level indicator)
A measurement of how the service is doing, such as the share of requests that succeed.
+ SLO (service level objective)
Your target for an SLI, such as 99.9% of requests succeed each month.
+ SLA (service level agreement)
The promise in a contract, usually with penalties if you miss it.
+ Error budget
How much failure your SLO allows. Spend it on shipping and on experiments.
+ MTTR
Mean time to recovery: how long, on average, it takes to restore service.
+ RTO
Recovery time objective: the longest you can afford to be down.
+ RPO
Recovery point objective: how much data you can afford to lose, measured in time.
+ Blast radius
How much of your system an experiment is allowed to affect.
+ Steady state
What normal looks like, measured, so you can tell when an experiment changes it.
+ GameDay
A planned exercise where a team breaks something on purpose and practises the response.
+ Fault injection
Deliberately introducing an error, delay or outage to test how a system responds.
+ Chaos engineering
The discipline of running controlled failure experiments to build confidence in a system.