SLA Comparison Chart: Nines, Downtime, and Cost Implications

SLA Comparison: From Two Nines to Six Nines

This chart compares every major SLA tier across multiple dimensions: downtime allowances, cost implications, typical architectures, and real-world examples.

Comprehensive SLA Comparison

SLA	Yearly Downtime	Monthly Downtime	Relative Cost	Architecture
99%	3d 15h 40m	7h 18m	1x (baseline)	Single instance
99.5%	1d 19h 49m	3h 39m	1.3x	Instance + monitoring
99.9%	8h 46m	43m 50s	2-3x	Multi-instance, LB
99.95%	4h 23m	21m 55s	3-5x	Multi-AZ
99.99%	52m 36s	4m 23s	5-10x	Multi-AZ + automation
99.999%	5m 16s	26s	20-50x	Multi-region active
99.9999%	31.5s	2.6s	100x+	Custom infrastructure

Architecture Requirements by Tier

99% — Single Instance:

• One server, manual deployments
• Basic monitoring (email alerts)
• No redundancy required

99.9% — Standard Production:

• Load balancer + 2+ instances
• Health checks, auto-restart
• Automated deployments
• Database with automated backups

99.99% — High Availability:

• Multi-AZ deployment
• Database replication with automatic failover
• Zero-downtime deployments (rolling/blue-green)
• On-call rotation with 5-minute response target
• Comprehensive monitoring and alerting

99.999% — Mission Critical:

• Multi-region active-active
• Global load balancing
• Chaos engineering practice
• Dedicated SRE team
• Sub-second automated failover

Cost Multipliers

The cost increase between tiers is not linear — it is roughly exponential:

99%    →  99.9%   : ~2-3x cost increase
99.9%  →  99.99%  : ~3-5x cost increase
99.99% →  99.999% : ~5-10x cost increase

Each additional nine costs more than the last because you are eliminating increasingly rare failure modes, which requires increasingly sophisticated (and expensive) countermeasures.

Choosing the Right Tier

Ask these questions:

1. What is the cost of downtime per minute for your business?
2. What is the infrastructure cost to achieve each tier?
3. Where does the breakeven point fall?

If downtime costs you $1,000/minute and upgrading from 99.9% to 99.99% costs $5,000/month extra, the ~39 minutes of saved downtime per month is worth ~$39,000 — a clear win.