SLA (Service Level Agreement): an agreement on the level of service rendered between the service provider and the client. The main difference between an SLA and an ordinary contract is the detailed conditions of service availability and response time to incidents.
The terms and conditions also specify the rights and obligations of the parties, individual characteristics of the service.
The main points of SLA:
- Agreed uptime. If the contract specifies “24×7”, it means that the service must be available round-the-clock 7 days a week.
- Agreed technical support time. If, for example, the terms and conditions state “8×5”, then technical support is available during an 8-hour working day Monday through Friday.
- Downtime. The time from actual service interruption to restoration of service.
- Response time. The time within which the provider’s technical service is required to respond to an incident. The starting point is the creation of a request by the client, and the ending point is the successful fulfillment of the request by the engineering service specialists.
The key SLA metric is actual availability. This parameter defines the guaranteed availability of the service for a certain period (usually a year).
For example, data centers and providers in SLA for their services declare the possible availability time of hardware or services in percent. Usually it is at least 99%. The higher the number after the decimal point, the better and safer the service is, but also more expensive at the same time.
| SLA value | |
| Actual availability | Maximum downtime per year |
| 99% | 3.65 days |
| 99.9% | 8.76 hours |
| 99.95% | 4.38 hours |
| 99.99% | 52.56 minutes |
| 99.999% | 5.26 minutes |