# SLA (Service Level Agreement)

URL: https://softwaredictionary.org/terms/sla
Category: DevOps & Cloud
Last updated: 2026-10-03
Pronunciation: es-el-AY

In short: An SLA (service level agreement) is a provider's commitment to customers about the level of service, such as 99.9% uptime, and what happens if it isn't met.

## What is an SLA?

An SLA turns reliability into a promise. A cloud database might guarantee 99.95% monthly availability, a support plan might promise a first response within an hour, and an API might commit to a maximum error rate. If the provider falls short, the agreement says what the customer gets, typically a credit off the bill.

The number of nines matters more than it looks. 99.9% availability allows about 43 minutes of downtime in a 30-day month, while 99.99% allows only about 4.3 minutes. Each extra nine requires more redundancy, automation and on-call effort, so higher SLAs cost much more to provide.

SLAs sit on top of two internal ideas from site reliability engineering. A service level indicator (SLI) is the measurement, such as the share of successful requests; a service level objective (SLO) is the internal target for it. Teams set their SLOs stricter than the SLA, so they get warned and can act before a contractual promise is broken.

A common misconception is that a service's availability is the same as its SLA. An application built on several services multiplies their risks: if it depends on three components that are each 99.9% available, its own availability is lower than any one of them, unless it is designed to tolerate their failures.

## Key takeaways

- An SLA is a formal promise about service quality, such as uptime.
- Missing it usually earns customers service credits.
- 99.9% allows about 43 minutes of downtime a month; 99.99% about 4.3 minutes.
- SLIs measure, SLOs set internal targets, and SLAs make external promises.
- Dependencies combine, so a system can be less available than its parts.

## Frequently asked questions

**What is the difference between an SLA, an SLO and an SLI?**

An SLI is a measurement, such as the percentage of successful requests. An SLO is the target a team sets for it. An SLA is the agreement with customers, with consequences if the promised level isn't met.

**What does 99.9% uptime mean?**

The service is available at least 99.9% of the time in the measured period, which allows about 43 minutes of downtime in a 30-day month, or nearly 9 hours over a year.

**What happens when an SLA is breached?**

Usually the customer can claim a service credit, a percentage of the monthly fee depending on how far availability fell. Serious or repeated breaches may allow the customer to end the contract.

---

Software Dictionary: https://softwaredictionary.org/ · https://softwaredictionary.org/llms.txt