📊 SLOs vs SLAs
These terms are closely related but serve different purposes in service reliability and contracts.
1️⃣ SLA – Service Level Agreement
Definition:
SLA is a formal contract between a service provider and a customer that defines the expected level of service.
Key Points:
- Legal/business contract.
- Specifies metrics like uptime, response time, support availability.
- Often includes penalties if not met.
Example:
- Cloud provider SLA: “99.9% uptime per month. If below, customer gets 10% credit.”
Formula for uptime SLA:
Uptime SLA = (Total Time – Downtime) / Total Time * 100%
2️⃣ SLO – Service Level Objective
Definition:
SLO is an internal target or goal for the service provider to meet the SLA.
Key Points:
- Focused on specific measurable metrics.
- Helps track and maintain SLA compliance.
- Usually internal to teams, not a contract.
Example:
- API service SLO: “99.95% of requests respond within 200ms per week.”
- Helps operations team stay within SLA targets.
3️⃣ Relationship Between SLA & SLO
SLA (Contract) → defines customer-facing expectation
SLO (Objective) → defines internal target to meet SLA
- SLOs are like checkpoints to ensure you meet the SLA.
- Example:
| Component | SLA (Customer-facing) | SLO (Internal Target) |
|---|---|---|
| API Availability | 99.9% uptime/month | 99.95% uptime/week |
| Response Time | 200ms per request | 190ms 95th percentile |
| Error Rate | <1% | <0.8% |
4️⃣ Benefits
- SLA: Protects customers, sets expectations, defines recourse.
- SLO: Helps engineering teams monitor, improve, and prevent SLA violations.
- Together: Drive reliability and accountability in services.
💡 Analogy:
- SLA = “Doctor promises patient a 99% recovery rate.”
- SLO = “Doctor aims to give each patient daily checkups and proper medication to achieve 99% recovery.”