SLA (service level agreement)
Also called service level agreement.
A contract that promises a level of service, such as uptime or support response time, and says what happens if it is missed.
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What it is.
An SLA turns reliability into a promise. A typical one covers uptime (for example 99.9% a month), support response times by severity, how outages are measured, what is excluded, and the remedy, usually service credits.
Google's SRE book draws the line clearly: an SLO is an internal target, and an SLA is the agreement that says what happens when targets are missed. If there is no consequence, it is an SLO, not an SLA.
Why it matters
An SLA tells a buyer what they can rely on and what they get if it fails. For a supplier, it sets the bar the system and the support team must be built to meet. Promising more than the architecture can deliver is expensive.
In a product build
When a build includes ongoing support, the SLA terms should match the hosting, monitoring and on-call setup that was actually built. OceanLab publishes a 99.9% uptime figure on its homepage.
Common mistakes.
- 01
Setting the SLA equal to the internal target, which leaves no safety margin.
- 02
Vague measurement: whose monitoring counts, and is slow the same as down?
- 03
Excluding so much (maintenance, third parties) that the promise means little.
Read the official text.
Primary sources this definition is based on.
- Google SRE book, Service Level Objectiveschecked 2026-10-25
Work it out with a tool.
Related terms.
- SLO (service level objective)An internal reliability target for a service, such as 99.9% of requests succeeding, measured by a service level indicator (SLI).
- UptimeThe share of time a service is working and reachable, usually written as a percentage such as 99.9%.
- RTO (recovery time objective)How long a system can stay down after a failure before the outage seriously harms the business.
- RPO (recovery point objective)The point in time to which data must be recoverable after an outage: in practice, how much recent data you can afford to lose.
Guides and pages
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