Understanding SLO-Based Alerting
Why does a 5% error rate trigger an alert at 2 AM? Is it catastrophic during peak traffic or meaningless during low usage? Traditional static thresholds can’t tell you. SLO-based alerting asks a better question: “Are we consuming our error budget faster than planned?” This approach ties alerts directly to user-impacting reliability issues, eliminating arbitrary thresholds and reducing alert fatigue while catching real problems early.
What is an SLO?
An SLO is a target reliability level for a service, expressed as a percentage. For example, a 99.9% availability SLO means your service should be available 99.9% of the time over a given period.
Why SLO-Based Alerting?
Traditional alerting often uses static thresholds like “alert if error rate > 5%”. This approach has problems:
- Context-free: 5% errors might be fine during low traffic, but catastrophic during peak hours
- Alert fatigue: Too many alerts that don’t correlate with user impact
- Arbitrary thresholds: Why 5%? Why not 4% or 6%?
SLO-based alerting solves these by asking: “Are we consuming our error budget faster than planned?”
Error Budget and Burn Rate
Your error budget is how much failure you can tolerate: 100% - SLO target. For a 99.9% SLO, you have a 0.1% error budget.
Burn rate measures how quickly you’re consuming this budget relative to the SLO period. A burn rate of 1.0 means you’re on track to exactly meet your SLO. A burn rate of 14.4 means you’ll exhaust your entire monthly budget in 2 days!
Multi-Window, Multi-Burn-Rate Alerts
Our alert generator creates alerts based on Google’s SRE workbook recommendations:
- Fast burn (critical): 14.4x burn rate over 1 hour + 1 hour lookback
- Slow burn (warning): 6x burn rate over 6 hours + 6 hour lookback
This approach balances:
- Precision: Short windows catch issues quickly
- Recall: Longer windows reduce false positives
Getting Started
Use our Alert Generator to create SLO-based alerting rules for your Prometheus setup. Simply provide:
- Your SLO target (e.g., 99.9%)
- Success/failure metrics
- SLO window (typically 30 days)
The generator creates all necessary recording rules and multi-window alerts ready to use with Prometheus.
Learn More
- Read the Google SRE Workbook chapter on SLO alerting
- Check our FAQ for common questions
- Try our Alert Generator now