Estimate NAT Gateway GB processed (quick methods)

NAT Gateway processing charges scale with GB processed, so your budget depends on getting this number roughly right. The goal isn’t perfection — it’s a defensible baseline plus a peak/incident scenario. Use the method that matches the data you have today, then validate with metrics later.

Method 1) From NAT metrics (best)

1. Pick a representative window (7–30 days) and sum bytes processed.
2. Convert bytes → GB using the same convention you use for pricing (and keep it consistent).
3. Scale to monthly: GB/month ≈ GB/window × (30 / days in window).

Use this whenever possible because it directly measures the billed driver.

Method 2) From VPC Flow Logs (good for attribution)

Flow logs are useful when you need to answer “what produced the GB?”. A practical workflow:

1. Filter flow logs to traffic that traverses NAT gateway ENIs.
2. Group by destination (top domains/IPs) and source (top subnets/workloads).
3. Sum bytes and convert to GB/month.

This method is slower but helps you find the 2–3 sources that actually matter (images, updates, external APIs).

Method 3) From throughput charts (Mbps) (fast first pass)

If you only have an “average Mbps” chart, you can estimate monthly GB with a units converter. Steps:

1. Start from average Mbps (not peak).
2. Apply utilization: if the chart is peak, multiply by an average factor you can defend.
3. Convert Mbps → GB/month with consistent units.

Tool: Units converter

Method 4) Sanity-check from common sources (useful when data is missing)

If you have no metrics yet, estimate the big buckets and add them:

• Image pulls: image size × pulls/month × fleet size
• Updates: update GB/week × nodes × weeks/month
• External APIs: requests/month × avg payload size (GB)
• Log shipping: log export GB/day × days/month

This is crude but helps you avoid pretending it’s zero.

Worked example (structure, not provider-specific rates)

• Representative week metrics: 1.2 TB processed in 7 days
• Scale to month: (1.2 TB / 7) × 30 ≈ 5.1 TB/month
• Price: 5.1 TB × $/GB + gateway-hours × $/hour

Validation checklist

• Compare estimate vs real processed-bytes metrics for a week after deployment.
• Identify the top 3 sources (images, updates, APIs) and verify they match expectations.
• Include an incident scenario: retries often dominate monthly peaks.
• After changes, confirm GB processed dropped (not just moved to transfer/egress elsewhere).

Next steps

Sources

• Amazon VPC pricing (NAT Gateway pricing)
• VPC Flow Logs documentation

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