Calculator Inputs
Fill costs in your billing currency; results display with a dollar sign for readability.
Example Data Table
This sample shows a typical multi-zone setup with replicated storage and a standby database.
| Input | Example Value | Notes |
|---|---|---|
| Primary instances | 2 | Baseline workload capacity. |
| Secondary instances | 2 | Active-Active for failover readiness. |
| Replication copies | 2 | One extra storage copy. |
| Storage | 2000 GB | Persistent volume + object storage mix. |
| Replication traffic | 500 GB/month | Cross-zone data synchronization. |
| Load balancers | 2 | Regional + global entry point. |
| DB replicas | 1 | Standby node for continuity. |
| Result highlight | Monthly total + incremental HA spend | Use for budgeting and comparison. |
Formula Used
- Primary compute = Primary instances × Monthly cost per instance
- Secondary compute = Secondary instances × Monthly cost per instance × Secondary cost factor
- Load balancers = Load balancers × Cost per load balancer
- Storage = Storage (GB) × Replication copies × Storage cost per GB-month
- Replication traffic = Replication traffic (GB) × Traffic cost per GB
- DB replicas = DB replicas × Cost per DB replica
- Setup amortized = One-time setup cost ÷ Amortize months
- Total monthly HA cost = Sum of all monthly components
- Baseline estimate = Primary compute + 1 load balancer + 1 storage copy + Operations
- Incremental HA spend = Total monthly HA cost − Baseline estimate
- Downtime hours/year = (1 − Availability%) × 8760
- Outage cost/year = Downtime hours/year × Downtime cost per hour
How to Use This Calculator
- Enter your primary instance count and monthly unit cost.
- Select redundancy mode and set secondary instance details.
- Fill network, storage replication, and data transfer fields.
- Add database replica, monitoring, backup, and support costs.
- Optionally model downtime cost and availability targets.
- Click Calculate and review totals, baseline, and incremental spend.
- Download CSV or PDF for budgeting and stakeholder review.
Professional Notes
Cost drivers in highly available designs
High availability spending typically clusters into compute redundancy, network entry points, replicated storage, and data-layer replicas. Compute costs rise linearly with instance counts, while load balancers add fixed monthly charges and sometimes per‑GB processing. Replicated storage multiplies the GB footprint by the number of copies, which is why small retention decisions can shift totals materially. Include ancillary services such as IPs, health checks, and cross-zone DNS where they apply to your architecture.
Active-Active versus Active-Passive budgeting
Active-Active configurations keep both zones serving traffic, often mirroring primary capacity and consuming similar reserved commitments. Active-Passive models usually run reduced standby capacity, using a secondary cost factor to represent smaller shapes, warm pools, or paused services. When forecasting, compare incremental spend against a single-zone baseline to make the “extra resiliency” price explicit for stakeholders. Also document performance expectations during failover, because undersized standby capacity can create hidden business risk.
Replication, storage multipliers, and transfer fees
Replication has two distinct cost surfaces: storage multiplication and data transfer. Even if storage is inexpensive, inter-zone or inter-region transfer fees can dominate for write-heavy systems and chatty databases. Track monthly replicated GB separately from customer egress, and confirm whether your provider prices transfer asymmetrically across regions. For object stores, verify lifecycle tiers and replication class, since cross-account replication may carry additional request charges.
Operations overhead and setup amortization
High availability is also an operations program, not only an infrastructure bill. Monitoring, alerting, backups, and runbook testing add recurring charges, while architecture and migration tasks appear as one-time setup. Amortizing setup across 12–24 months produces a planning-friendly monthly figure that aligns with budgeting cycles and renewal discussions. Pair costs with measurable controls, such as recovery time objective testing frequency and automated backup validation success rates.
Linking availability targets to downtime economics
Availability targets can be translated into expected downtime using 8,760 hours per year. For example, 99.5% allows about 43.8 hours annually, while 99.95% allows about 4.38 hours. If you attach an hourly downtime cost, you can estimate avoided outage losses and compare them to annual incremental HA spend. This framing aligns choices with SLAs.
FAQs
What is incremental HA spend in this calculator?
It is the monthly difference between the high availability design total and a simplified single-zone baseline estimate, highlighting the added resiliency budget.
How should I choose Active-Active versus Active-Passive?
Use Active-Active when both zones must serve traffic continuously. Use Active-Passive when a reduced standby is acceptable. Compare the cost factor and failover capacity needs.
Does replicated storage always double my storage bill?
Not always. Costs depend on the number of copies, storage class, and retained versions. Some services add request charges. Enter your exact replication copies and GB rate for accuracy.
Why include replication traffic separately from egress?
Cross-zone or cross-region synchronization can be billed differently than customer egress. Measuring replicated GB helps capture hidden transfer costs in write-heavy workloads.
How do availability percentages translate to downtime?
Downtime hours per year equal (1 − availability) × 8,760. Higher targets reduce expected downtime sharply, especially when moving from two nines to three or four nines.
Can the downtime savings estimate be trusted as ROI?
Treat it as a planning lens. Use realistic outage cost inputs, consider partial degradation events, and validate assumptions with incident history and SLA penalty terms.