SLA, SLO, and SLI Explained

Measure, target, and guarantee service reliability — using indicators, objectives, and agreements to balance feature velocity with system dependability.

SLA, SLO, and SLI

SLAs, SLOs, and SLIs are a hierarchy of service reliability metrics: SLIs measure performance indicators, SLOs set internal reliability targets, and SLAs are contractual commitments with consequences for violations.

Explanation

Service Level Indicators (SLIs) are the actual measurements: request latency, error rate, availability percentage, throughput. Service Level Objectives (SLOs) set targets for SLIs: "99.9% of requests complete within 200ms." SLOs are internal goals that inform engineering priorities. Service Level Agreements (SLAs) are contractual commitments to customers with defined consequences (credits, refunds) if violated. The relationship is: SLIs measure reality, SLOs define aspirations, SLAs define obligations. SLOs should be stricter than SLAs to provide a safety margin. Error budgets (the allowed unreliability) determine when teams focus on features vs reliability.

Bookuvai Implementation

Bookuvai defines SLIs, SLOs, and SLAs for every production application. We implement automated SLI measurement through monitoring, track SLO compliance in dashboards, and configure alerts when error budgets are being consumed too quickly. This data-driven approach balances feature velocity with reliability.

Key Facts

  • SLI: measured metric (latency, error rate, availability)
  • SLO: internal target for SLIs (99.9% availability)
  • SLA: contractual commitment with consequences for violations
  • Error budgets: allowed unreliability that enables feature velocity
  • SLOs should be stricter than SLAs to provide safety margin

Related Terms

Frequently Asked Questions

What is an error budget?
An error budget is the allowed unreliability: if your SLO is 99.9% availability, your error budget is 0.1% (about 43 minutes of downtime per month). When the budget is consumed, teams prioritize reliability over features. This balances innovation with stability.
Should every service have an SLA?
Every service should have SLOs (internal targets), but SLAs (contractual commitments) are only needed for customer-facing services where violations have financial consequences. Internal services use SLOs without the contractual overhead.
How do I choose the right SLO target?
Start by measuring current performance (SLIs) and user expectations. Set SLOs that are achievable but aspirational. 99.9% availability (8.7 hours downtime per year) is common for web services. Avoid over-committing: 99.99% is 10x harder than 99.9%.