Definition: Internal objective defining the desired reliability level for a service, stricter than the SLA and used as an operational target by engineering teams.
— Source: NERVICO, Product Development Consultancy
What Is an SLO
A Service Level Objective (SLO) is an internal reliability objective that establishes the service level an engineering team commits to maintaining. Unlike the SLA, which is an external contractual commitment, the SLO is an internal operational target typically set more strictly. If the SLA commits to 99.9% availability, the SLO might be set at 99.95% to maintain a safety margin before violating the contract.
How It Works
SLOs are defined from SLIs (measurable indicators) and expressed as a target percentage over a time period. For example, “99.95% of HTTP requests must complete in under 200ms over a 30-day period.” The key concept is the error budget: if the SLO is 99.95%, the team has a 0.05% error budget it can consume without consequences. While error budget is available, the team can prioritize feature development. When the error budget is exhausted, priority shifts to reliability.
Key Use Cases
- Establishing operational targets for platform engineering and site reliability engineering (SRE) teams
- Managing error budgets to balance development velocity with service stability
- Proactive alerting when error budget burn rate indicates risk of SLA violation
- Informed negotiation of external SLAs based on historical internal SLO compliance data
Advantages and Considerations
SLOs provide an objective framework for deciding between development velocity and reliability. The error budget concept transforms the tension between product and operations teams into a data-driven decision. The main consideration is that SLOs must be realistic and reviewed periodically. An overly ambitious SLO will consume excessive resources on reliability, while an overly permissive one will not protect the team from violating the SLA.