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SLO/SLI Definitions

19. 04. 2023 Updated: 27. 03. 2026 1 min read intermediate
This article was published in 2023. Some information may be outdated.

DevOps Intermediate

SLO/SLI Definitions

SLOSLISRE 3 min read

Service Level Indicators a Objectives. Merit spolehlivost.

SLI a SLO

Service: API
SLO: 99.9% availability (mesicne)
SLI: successful_requests / total_requests
Error Budget: 0.1% = ~43 min downtime/mesic

How to Define Proper SLIs and SLOs

When defining SLIs, start from the user experience, not internal metrics. A good SLI for an API is the ratio of successful responses (status < 500) with latency under 300ms to total requests. The SLO should be ambitious enough to ensure quality but not so strict that it blocks development.

Typical SLOs for different services: web API 99.9% (43 min downtime/month), internal batch processing 99.5% (3.6 h/month), critical financial services 99.99% (4.3 min/month). The SLA (Service Level Agreement) is a contractual commitment to the customer that should always be less strict than the internal SLO — if the SLO is 99.9%, the SLA should be 99.5%. Monitor SLIs in real time using Prometheus + Grafana and set up alerting on burn rate — how quickly you are consuming your error budget.

Shrnuti

SLO = cilova spolehlivost. SLI = mereni. Error budget = prostor pro inovaci.

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