In Azure, both a Standard Load Balancer (with outbound rules) and a NAT Gateway can provide a shared static outbound public IP address for multiple virtual machines (VMs), allowing outbound traffic to use a consistent, fixed IP (e.g., for whitelisting purposes). This setup uses Source Network Address Translation (SNAT) to map private VM IPs to the public IP. However, the Load Balancer is generally the cheaper option based on current pricing, as it has a lower hourly rate and significantly lower data processing fees. NAT Gateway is recommended for larger-scale scenarios to avoid SNAT port exhaustion (it supports up to 64,000 ports per IP vs. ~1,024 pre-allocated ports per VM IP config on Load Balancer), but if your workload doesn’t risk port exhaustion, Load Balancer will cost less.
Key Pricing Comparison (East US Region, Pay-As-You-Go, Approximate Monthly Estimates)
Pricing excludes taxes, reservations, or discounts and assumes ~730 hours/month. Both require a Standard Public IP (~$2.60/month for a static IPv4 address). Azure also charges separately for outbound data transfer (bandwidth/egress: first 5 GB free, then ~$0.087/GB), which is the same for both options.
| Component | Standard Load Balancer (Outbound Rules) | NAT Gateway |
|---|---|---|
| Hourly Service Charge | ~$0.025/hour (~$18.25/month) for the balancer with up to 5 rules (first 5 free; additional rules ~$0.008/rule/hour). No charge if no rules configured. | ~$0.045/hour (~$32.85/month). Charged from creation, regardless of attachments. |
| Data Processing | ~$0.005/GB (inbound + outbound through the balancer). | ~$0.045/GB (outbound + return/response traffic). |
| Public IP (Required) | ~$0.0036/hour (~$2.60/month). Can use up to 16 IPs for scale. | Same as Load Balancer (~$2.60/month). Can use up to 16 IPs or a prefix for scale. |
| Example Monthly Cost (No Data Transfer) | ~$20.85 (balancer + public IP). | ~$35.45 (gateway + public IP). |
| Example Monthly Cost (100 GB Outbound + 100 GB Inbound/Response) | ~$21.85 (balancer + public IP + ~$1 data processing). Plus ~$8.70 bandwidth for outbound. | ~$44.45 (gateway + public IP + ~$9 data processing). Plus ~$8.70 bandwidth for outbound. |
| Other Notes | – Cheaper for low-to-moderate data volumes. – Data processing applies only to traffic via the balancer. – Inbound NAT/load-balancing rules can be added at no extra hourly cost (up to 5 total rules). | – ~40-80% more expensive overall. – Data processing includes all outbound/return traffic. – Simpler for pure outbound; no need for backend pools/rules if not load balancing. |
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