Introduction
In 2023, a major airline’s IT outage stranded thousands of passengers, costing millions in lost revenue and trust. Meanwhile, companies like AWS and Zoom thrive by pairing Service Level Objectives (SLOs) with Service Level Agreements (SLAs)—clear targets that balance innovation with accountability.
This post breaks down how SLOs and SLAs work, why they matter, and how to implement them effectively.
1. SLOs vs. SLAs: Defining the Duo
| Term | Purpose | Actor | Example |
|---|---|---|---|
| SLO | Internal reliability goal (e.g., uptime, latency). | Engineering teams | “99.9% of requests complete in <1 second.” |
| SLA | Customer-facing promise with penalties for failure. | Users | “99.9% uptime or service credits.” |
Analogy:
- SLO: A chef’s target to prep meals in 15 minutes (internal).
- SLA: The restaurant’s promise to comp your meal if it’s late (external).
2. Why SLOs and SLAs Matter
For Businesses
- Build Trust: Transparent SLAs help retain customers.
- Focus Efforts: SLOs align teams on critical metrics.
For Users
- Clarity: Clearly defined service expectations.
- Accountability: SLAs provide recourse for service failures.
Example:
AWS guarantees 99.99% uptime for EC2 instances. If this is unmet, customers receive service credits.
3. How to Define Effective SLOs
Step 1: Identify Critical User Journeys
Focus on metrics that directly impact user satisfaction:
- E-commerce: Checkout success rate.
- Streaming: Video start time.
Example:
Slack prioritizes message delivery speed, setting SLOs around latency.
Step 2: Set Realistic Targets
- Use historical data (e.g., past uptime figures).
- Balance ambition with engineering capacity.
Framework:
Consider Google’s “Four Golden Signals”: latency, traffic, errors, and saturation.
Step 3: Align with Stakeholders
- Engineering: Ensure technical feasibility.
- Business: Align with revenue-critical workflows.
Case Study:
Zoom sets SLOs for video latency, ensuring seamless calls even during peak usage.
4. Crafting Enforceable SLAs
Key Components
- Scope: Define covered services (e.g., API uptime).
- Metrics: Establish how performance is measured (e.g., monthly uptime).
- Remedies: Specify penalties for breaches (e.g., refunds or service credits).
Example:
Microsoft Azure offers financial credits when uptime falls below 99.9%.
Pitfalls to Avoid
- Overpromising: Avoid setting SLAs that are stricter than your internal SLOs.
- Vagueness: Clearly define metrics (e.g., “99.9% uptime,” not “high availability”).
5. Tools to Track SLOs/SLAs
| Tool | Use Case |
|---|---|
| Prometheus | Track error rates and latency. |
| Grafana | Visualize uptime trends. |
| Dynatrace/NewRelic | Monitor end-to-end service health. |
6. The Future of SLOs/SLAs
- AI-Driven SLOs: Tools that auto-suggest targets based on usage patterns.
- Dynamic SLAs: Adjust commitments in real-time (e.g., higher credits during holidays).
7. Conclusion
SLOs and SLAs transform reliability from abstract ideals into measurable commitments. By aligning internal goals with customer promises, teams can innovate confidently while keeping users loyal.
Pro Tip: Start with one SLO for your most critical service. Refine it over time, then build your SLA.
Coming Up Next
Learn how Error Budgets let teams ship features without breaking reliability.