SLI
Service Level Indicator
ELI5 — The Vibe Check
An SLI is the actual measurement you track to know if you're hitting your SLO. If the SLO says 'be fast,' the SLI is the actual timer measuring speed. SLI: the number. SLO: the target. SLA: the contract. They form a hierarchy — you can't have the others without real measurements.
Real Talk
A Service Level Indicator is a quantitative measure of some aspect of service behavior, such as request latency, error rate, or availability percentage. SLIs are the raw metrics that are compared against SLO targets. Choosing the right SLIs requires careful thought about what matters to users.
When You'll Hear This
"Our primary SLI is the percentage of successful requests over 5-minute windows." / "Define your SLIs before setting SLOs — measure first, target second."
Related Terms
Metrics
Metrics are the numbers your app tracks about itself over time — requests per second, error rate, CPU usage, response time, active users.
Monitoring
Monitoring is keeping a constant eye on your app while it runs — tracking whether it's up, how fast it responds, how many errors it throws, and how much me...
SLA (Service Level Agreement)
An SLA is a contract between you and your users about how reliable your service will be. 'We promise the app will be up 99.9% of the time.
SLO (Service Level Objective)
An SLO is the internal target you set for how well your service should run. It's like a personal fitness goal vs a race you signed up for.
SRE (Site Reliability Engineering)
SRE is Google's version of DevOps with a more engineering-focused twist.