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SLO Implementation
Framework for defining and implementing Service Level Indicators (SLIs), Service Level Objectives (SLOs), and error budgets.
Purpose
Implement measurable reliability targets using SLIs, SLOs, and error budgets to balance reliability with innovation velocity.
When to Use
- Define service reliability targets
- Measure user-perceived reliability
- Implement error budgets
- Create SLO-based alerts
- Track reliability goals
SLI/SLO/SLA Hierarchy
SLA (Service Level Agreement)
↓ Contract with customers
SLO (Service Level Objective)
↓ Internal reliability target
SLI (Service Level Indicator)
↓ Actual measurementDefining SLIs
Common SLI Types
1. Availability SLI
promql
# Successful requests / Total requests
sum(rate(http_requests_total{status!~"5.."}[28d]))
/
sum(rate(http_requests_total[28d]))2. Latency SLI
promql
# Requests below latency threshold / Total requests
sum(rate(http_request_duration_seconds_bucket{le="0.5"}[28d]))
/
sum(rate(http_request_duration_seconds_count[28d]))3. Durability SLI
# Successful writes / Total writes
sum(storage_writes_successful_total)
/
sum(storage_writes_total)Reference: See references/slo-definitions.md
Setting SLO Targets
Availability SLO Examples
| SLO % | Downtime/Month | Downtime/Year |
|---|---|---|
| 99% | 7.2 hours | 3.65 days |
| 99.9% | 43.2 minutes | 8.76 hours |
| 99.95% | 21.6 minutes | 4.38 hours |
| 99.99% | 4.32 minutes | 52.56 minutes |
Choose Appropriate SLOs
Consider:
- User expectations
- Business requirements
- Current performance
- Cost of reliability
- Competitor benchmarks
Example SLOs:
yaml
slos:
- name: api_availability
target: 99.9
window: 28d
sli: |
sum(rate(http_requests_total{status!~"5.."}[28d]))
/
sum(rate(http_requests_total[28d]))
- name: api_latency_p95
target: 99
window: 28d
sli: |
sum(rate(http_request_duration_seconds_bucket{le="0.5"}[28d]))
/
sum(rate(http_request_duration_seconds_count[28d]))Error Budget Calculation
Error Budget Formula
Error Budget = 1 - SLO TargetExample:
- SLO: 99.9% availability
- Error Budget: 0.1% = 43.2 minutes/month
- Current Error: 0.05% = 21.6 minutes/month
- Remaining Budget: 50%
Error Budget Policy
yaml
error_budget_policy:
- remaining_budget: 100%
action: Normal development velocity
- remaining_budget: 50%
action: Consider postponing risky changes
- remaining_budget: 10%
action: Freeze non-critical changes
- remaining_budget: 0%
action: Feature freeze, focus on reliabilityReference: See references/error-budget.md
SLO Implementation
Prometheus Recording Rules
yaml
# SLI Recording Rules
groups:
- name: sli_rules
interval: 30s
rules:
# Availability SLI
- record: sli:http_availability:ratio
expr: |
sum(rate(http_requests_total{status!~"5.."}[28d]))
/
sum(rate(http_requests_total[28d]))
# Latency SLI (requests < 500ms)
- record: sli:http_latency:ratio
expr: |
sum(rate(http_request_duration_seconds_bucket{le="0.5"}[28d]))
/
sum(rate(http_request_duration_seconds_count[28d]))
- name: slo_rules
interval: 5m
rules:
# SLO compliance (1 = meeting SLO, 0 = violating)
- record: slo:http_availability:compliance
expr: sli:http_availability:ratio >= bool 0.999
- record: slo:http_latency:compliance
expr: sli:http_latency:ratio >= bool 0.99
# Error budget remaining (percentage)
- record: slo:http_availability:error_budget_remaining
expr: |
(sli:http_availability:ratio - 0.999) / (1 - 0.999) * 100
# Error budget burn rate
- record: slo:http_availability:burn_rate_5m
expr: |
(1 - (
sum(rate(http_requests_total{status!~"5.."}[5m]))
/
sum(rate(http_requests_total[5m]))
)) / (1 - 0.999)SLO Alerting Rules
yaml
groups:
- name: slo_alerts
interval: 1m
rules:
# Fast burn: 14.4x rate, 1 hour window
# Consumes 2% error budget in 1 hour
- alert: SLOErrorBudgetBurnFast
expr: |
slo:http_availability:burn_rate_1h > 14.4
and
slo:http_availability:burn_rate_5m > 14.4
for: 2m
labels:
severity: critical
annotations:
summary: "Fast error budget burn detected"
description: "Error budget burning at {{ $value }}x rate"
# Slow burn: 6x rate, 6 hour window
# Consumes 5% error budget in 6 hours
- alert: SLOErrorBudgetBurnSlow
expr: |
slo:http_availability:burn_rate_6h > 6
and
slo:http_availability:burn_rate_30m > 6
for: 15m
labels:
severity: warning
annotations:
summary: "Slow error budget burn detected"
description: "Error budget burning at {{ $value }}x rate"
# Error budget exhausted
- alert: SLOErrorBudgetExhausted
expr: slo:http_availability:error_budget_remaining < 0
for: 5m
labels:
severity: critical
annotations:
summary: "SLO error budget exhausted"
description: "Error budget remaining: {{ $value }}%"SLO Dashboard
Grafana Dashboard Structure:
┌────────────────────────────────────┐
│ SLO Compliance (Current) │
│ ✓ 99.95% (Target: 99.9%) │
├────────────────────────────────────┤
│ Error Budget Remaining: 65% │
│ ████████░░ 65% │
├────────────────────────────────────┤
│ SLI Trend (28 days) │
│ [Time series graph] │
├────────────────────────────────────┤
│ Burn Rate Analysis │
│ [Burn rate by time window] │
└────────────────────────────────────┘Example Queries:
promql
# Current SLO compliance
sli:http_availability:ratio * 100
# Error budget remaining
slo:http_availability:error_budget_remaining
# Days until error budget exhausted (at current burn rate)
(slo:http_availability:error_budget_remaining / 100)
*
28
/
(1 - sli:http_availability:ratio) * (1 - 0.999)Additional patterns and templates
More detailed templates and worked examples live in references/details.md. Read that file for the full pattern library.
