A service level agreement (SLA) is the contractual assurance of measurable service quality: it defines metrics such as availability, response and recovery times, specifies how they are measured and reported, and regulates the consequences of missing them — usually service credits.
Good SLAs create clarity for both sides: the customer knows what to rely on; the provider knows what it is measured against. What matters is that the metrics fit the business — and do not just sound legally impressive.
What belongs in a solid SLA
- Availability with a clear definition: what counts as an outage, what as a maintenance window?
- Response and recovery times per severity — including service hours (8x5 to 24/7).
- Measurement and reporting: who measures how, and at what rhythm is it reported?
- Consequences of missing targets: service credits, escalation rights, termination options.
SLA, SLO and the service promise
Behind an SLA are internal service level objectives (SLOs) — the targets the operation is designed for. The SLA is the contractually promised lower bound of those. Important for managed services: a number like availability alone says little if reporting paths, escalation and communication during incidents are not equally well defined. A 99.9 percent promise without a defined response time is worth little when it matters.