Educational — Cloud egress & data-transfer cost guides. FinOps-lite estimators. Not a quote, broker, or savings guarantee. Launching soon where incomplete.
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nat-vpc · Educational

Cloud egress: ALB/NLB cross-zone data transfer vs instance cross-AZ

Application Load Balancer (ALB) and Network Load Balancer (NLB) cross-zone load balancing can move bytes between AZs on a different path template than instance-to-instance cross-AZ chatter or Internet DT-out. Map ELB LCU/NLCU hours, cross-zone GB, and InterZone lines separately — rates stay Unknown until verified.

Updated

Load-balancer cross-zone load balancing can meter differently from instance-to-instance cross-AZ and Internet DT-out — separate the bill lines.

Bill-line map (educational)

Bill-line map: ELB cross-zone vs instance cross-AZ vs Internet
Bill line / CE-style labelWhen it appearsPath templateSibling spoke
ELB / ALB LCU-hoursLoad balancer capacity unitsLB hours (not DT)CE decoder
NLB NLCU-hoursNetwork Load Balancer capacityLB hours (not DT)CE decoder
Cross-zone data transfer (LB)Cross-zone LB enabled; bytes across AZs via LBELB cross-zone DTThis spoke
InterZone / cross-AZ EC2Instance↔instance across AZsInstance cross-AZCross-AZ vs cross-region
Data Transfer–Out to InternetClient downloads leave AWSInternet DT-outFree-tier cliff
Processed bytes (ALB)ALB traffic processing dimensionsLB processing (verify SKU)CE decoder
Path matrix: ALB/NLB cross-zone vs instance cross-AZ vs Internet DT-out
PathMeters to modelBest whenFinOps note
Client → ALB (cross-zone on) → targets multi-AZLCU hours + cross-zone GB (verify) + target processingEven distribution across AZsDo not blend with Internet DT-out
Client → NLB (cross-zone on) → targets multi-AZNLCU hours + cross-zone GB (verify)TCP/UDP scale-outALB ≠ NLB SKUs
Instance-A → Instance-B cross-AZ (no LB)InterZone / cross-AZ DTMesh, replicas, chatty servicesCross-AZ spoke
Client → ALB/NLB → Internet responseInternet DT-out (+ LB hours)Public appsFree-tier cliff may apply
Cross-zone off, targets single AZ affinityFewer cross-zone GB; imbalance riskTight AZ localityAvailability trade-off ≠ savings guarantee

Sources (official AWS / ELB docs)

  1. Elastic Load Balancing pricing — as-of Unknown until verified
  2. What is an Application Load Balancer? — as-of
  3. What is a Network Load Balancer? — as-of
  4. How Elastic Load Balancing works (incl. cross-zone) — as-of
  5. EC2 data transfer / on-demand pricing — as-of Unknown until verified

Dated starting points only — no invented $/GB. Re-check ALB vs NLB cross-zone pricing rows before architecture changes.

Educational FinOps-lite only. Pair CE labels with this matrix and the cross-AZ vs cross-region spoke so HA chatter is not mistaken for customer downloads.

Path templates to model

Common traps

Blending ELB cross-zone GB with EC2 InterZone on one chart. Ignoring LCU/NLCU hours while optimizing only DT. Assuming NLB pricing matches ALB. Turning cross-zone off for “savings” without measuring availability impact. No guaranteed savings.

FinOps checklist

  1. List ALB/NLB with cross-zone setting and target AZ count.
  2. Export CE lines: LCU/NLCU, cross-zone DT, InterZone, Internet DT-out.
  3. Estimate client GB vs east-west GB separately.
  4. Model east-west with Mode A path=cross-az; keep rates Unknown.
  5. Read CE decoder · methodology.

Glossary: ELB cross-zone, cross-AZ, path template, Unknown until verified.

FinOps-lite Unknown until verified

Worked example (educational): 5 TB client downloads + 1.2 TB cross-zone via ALB

  1. Public ALB serves 5,000 GB/month to Internet clients; cross-zone load balancing moves an estimated 1,200 GB between AZs to balance targets.
  2. Line Internet DT-out × 5,000 GB — rate Unknown (watch free-tier cliff).
  3. Line ALB LCU-hours — rate Unknown.
  4. Line ELB cross-zone DT × 1,200 GB — rate Unknown (verify ALB pricing row).
  5. Optional: instance-to-instance cross-AZ mesh is a separate InterZone line — do not add it into #4 without evidence.
Numbered ALB scenario — Unknown rate cells
#Scenario lineVolumeUnit rate
1Internet DT-out (client downloads)5,000 GBUnknown $/GB
2ALB LCU-hoursmonthly LCUsUnknown $/LCU-hour
3ELB cross-zone data transfer1,200 GBUnknown $/GB
4Instance InterZone (if any)separate exportUnknown $/GB

Open calculator Mode A (cross-AZ) Cost Explorer decoder Cross-AZ vs cross-region

FAQ on this path

Does enabling cross-zone load balancing always add a data-transfer charge?

It depends on the load balancer type and current AWS pricing pages. Treat ALB vs NLB cross-zone bytes as separate path templates from instance-to-instance cross-AZ and Internet DT-out. Keep rates Unknown until verified on dated official docs.

Is ELB cross-zone the same meter as InterZone / cross-AZ on EC2?

Not necessarily. Load-balancer cross-zone traffic and instance-to-instance cross-AZ can appear as different bill lines. Use the Cost Explorer decoder and this matrix before blending.

Will turning off cross-zone guarantee savings?

No. PipeToll never guarantees savings. Disabling cross-zone can change availability and imbalance risk — measure bytes and architecture constraints first.