SLI
Definition
Service Level Indicator - specific metric that measures an aspect of service performance, providing insights into service quality and reliability.
Use Cases
- Google: Defining and tracking user-facing reliability for large-scale online services using measurable indicators (e.g., request success rate and latency) to guide reliability work. — Google’s Site Reliability Engineering (SRE) practices emphasize selecting a small set of meaningful SLIs (such as availability and latency), measuring them from real user requests, and using them to set SLOs and manage error budgets. (Teams use SLI/SLO signals to prioritize reliability improvements, balance feature velocity with stability, and make incident response and post-incident actions more data-driven.)
- Netflix: Monitoring streaming and API reliability to maintain a good customer experience during traffic spikes and regional failures. — Netflix is known for strong observability and resilience practices; teams commonly track service health using indicators like request success rate, latency percentiles, and availability across regions to detect regressions and guide operational decisions. (Improved ability to detect issues quickly, reduce customer-impacting outages, and make reliability trade-offs based on measurable service performance.)
Frequently Asked Questions
- What's the difference between an SLI and an SLO?
- An SLI is the metric you measure (for example, 99th percentile API latency or request success rate). An SLO is the target you set for that metric (for example, '99% of requests under 300 ms' or '99.9% successful requests over 30 days'). SLIs are measurements; SLOs are goals based on those measurements.
- When should I use SLIs?
- Use SLIs when you need an objective way to judge service health and user experience. They’re especially useful when you operate production services, need to set reliability targets, want to reduce alert noise by alerting on user-impacting symptoms, or want to make trade-offs between shipping features and improving stability.
- How much does SLI cost?
- Defining an SLI is free, but measuring it can cost money depending on your monitoring stack. Costs typically come from collecting and storing metrics/logs/traces, running dashboards and alerts, and any synthetic monitoring. Pricing varies by provider and by volume (number of metrics, data points, log GB ingested, trace spans, retention period, and alert evaluations).
Category: software
Difficulty: intermediate
Related Terms
See Also