Calculator Inputs
Enter realistic infrastructure, traffic, and failover assumptions. The result appears above this form after submission.
Plotly Graph
This chart compares monthly cost and estimated yearly downtime for the baseline and multi-zone design.
Example Data Table
| Scenario | Workload/AZ | Shared | Storage | Replication % | Inter-AZ GB | Rate | AZs | Availability % | Failover % | Outage Min/Yr |
|---|---|---|---|---|---|---|---|---|---|---|
| API Platform | $1,800 | $350 | $420 | 35 | 2,500 | $0.02 | 2 | 99.90 | 95 | 525.60 |
| Ecommerce Stack | $3,250 | $500 | $700 | 50 | 6,000 | $0.02 | 3 | 99.95 | 97 | 262.80 |
| Analytics Service | $2,200 | $400 | $580 | 40 | 3,400 | $0.015 | 2 | 99.80 | 92 | 1051.20 |
Formula Used
Single Cost = Workload per AZ + Shared Services + Storage + Backup + Monitoring/Ops
Multi Cost = (Workload per AZ × AZ Count) + Shared Services + Storage × (1 + Replication Overhead) + Backup + Monitoring/Ops × (1 + Ops Uplift) + Inter-AZ Data × Transfer Rate
Simultaneous Outage Minutes = 525,600 × (1 − Single-AZ Availability)AZ Count
Failover Loss Minutes = Single-AZ Outage × (1 − Failover Success Rate) ÷ AZ Count
Multi-AZ Downtime = Simultaneous Zone Outage + Failover Loss
Effective Availability = (1 − Multi-AZ Downtime ÷ 525,600) × 100
These equations are planning estimates. Real environments may have application-level limits, stateful bottlenecks, and provider-specific network pricing.
How to Use This Calculator
- Enter your current monthly workload cost for one zone.
- Add shared platform costs that remain regardless of zone count.
- Enter storage, backup, and monitoring costs.
- Choose how many zones you plan to use.
- Estimate replication overhead and monthly inter-zone traffic.
- Enter your observed or target single-zone availability.
- Set a realistic failover success rate based on drills or testing.
- Enter yearly outage minutes for the baseline design.
- Submit the form and review cost, downtime, and resilience outputs above the form.
- Use the CSV and PDF buttons to export your result summary.
FAQs
1. Why use a multi-AZ deployment?
It reduces service disruption risk by spreading workloads across separate zones. If one zone fails, healthy zones can continue serving traffic, improving continuity and customer experience.
2. Does multi-AZ replace backups?
No. Multi-AZ improves availability, while backups protect against deletion, corruption, ransomware, and recovery mistakes. Most production systems need both.
3. Is adding more zones always better?
Not always. More zones can improve resilience, but they also increase compute duplication, replication traffic, data consistency complexity, and operational overhead.
4. What does failover success rate represent?
It reflects how often automation, health checks, traffic switching, and dependent services recover correctly during an incident or planned failover exercise.
5. Why include inter-AZ transfer cost?
Cross-zone replication, clustering, logging, and east-west application traffic can materially increase monthly spend, especially for chatty or stateful systems.
6. Can this estimate managed database deployments?
Yes, as a planning model. Put database premiums into workload, storage, replication, and transfer inputs. Then validate against actual provider pricing.
7. What outage value should I enter?
Use observed yearly downtime from monitoring, incident reviews, or SLA history. If unavailable, start with your target assumption and refine later.
8. When is multi-AZ not worth it?
It may be excessive for low-impact internal tools, batch jobs, or workloads that tolerate downtime better than they tolerate permanent cost uplift.