Monitoring
Service Level Objective
SLO
SLO means Service Level Objective — the internal reliability target a team commits to, such as 99.9% of homepage requests returning in under 400ms over a rolling 30-day window. SLOs sit inside the SLA envelope and give engineering the numbers to code, alert, and prioritise against.
In depth
SLOs are the operational form of the SLA. Where the SLA promises the customer 99.5% uptime, the internal SLO is usually stricter (99.9%) so there is headroom before contract penalties kick in.
Each SLO has a service level indicator (SLI) that measures it — availability, latency, error rate, freshness. When the SLI drops below the SLO, the error budget shrinks; when it burns out, deploys freeze until reliability is restored.
Why it matters
SLOs replace argument with math. Instead of 'is this outage bad?' the team asks 'did this outage burn our error budget?'. That reframes reliability from vibes to a shared, quantitative constraint — and stops feature velocity from silently degrading uptime.
Related terms
SLA
A service level agreement (SLA) is a contractual commitment between a provider and a customer specifying a mea…
Error Budget
An error budget is the acceptable amount of unreliability inside an SLO — 1 minus the objective. A 99.9% SLO m…
Service Level Indicator
A Service Level Indicator (SLI) is the actual measurement of one aspect of service — usually availability, lat…
Uptime
Uptime is the percentage of time a website or service is reachable and serving correct responses. It is the he…
Mean Time Between Failures
Mean Time Between Failures (MTBF) is the average time a system operates between one incident and the next. MTB…
Browse the full Lemwatch monitoring glossary (47 terms).