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 2026-09-16

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 label	When it appears	Path template	Sibling spoke
ELB / ALB LCU-hours	Load balancer capacity units	LB hours (not DT)	CE decoder
NLB NLCU-hours	Network Load Balancer capacity	LB hours (not DT)	CE decoder
Cross-zone data transfer (LB)	Cross-zone LB enabled; bytes across AZs via LB	ELB cross-zone DT	This spoke
InterZone / cross-AZ EC2	Instance↔instance across AZs	Instance cross-AZ	Cross-AZ vs cross-region
Data Transfer–Out to Internet	Client downloads leave AWS	Internet DT-out	Free-tier cliff
Processed bytes (ALB)	ALB traffic processing dimensions	LB processing (verify SKU)	CE decoder

Path matrix: ALB/NLB cross-zone vs instance cross-AZ vs Internet DT-out
Path	Meters to model	Best when	FinOps note
Client → ALB (cross-zone on) → targets multi-AZ	LCU hours + cross-zone GB (verify) + target processing	Even distribution across AZs	Do not blend with Internet DT-out
Client → NLB (cross-zone on) → targets multi-AZ	NLCU hours + cross-zone GB (verify)	TCP/UDP scale-out	ALB ≠ NLB SKUs
Instance-A → Instance-B cross-AZ (no LB)	InterZone / cross-AZ DT	Mesh, replicas, chatty services	Cross-AZ spoke
Client → ALB/NLB → Internet response	Internet DT-out (+ LB hours)	Public apps	Free-tier cliff may apply
Cross-zone off, targets single AZ affinity	Fewer cross-zone GB; imbalance risk	Tight AZ locality	Availability trade-off ≠ savings guarantee

Sources (official AWS / ELB docs)

Elastic Load Balancing pricing — as-of 2026-09-09 Unknown until verified
What is an Application Load Balancer? — as-of 2026-09-09
What is a Network Load Balancer? — as-of 2026-09-09
How Elastic Load Balancing works (incl. cross-zone) — as-of 2026-09-09
EC2 data transfer / on-demand pricing — as-of 2026-09-09 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

ALB cross-zone on — LCU + any cross-zone GB SKU + target AZ placement.
NLB cross-zone on — NLCU + verify whether cross-zone bytes bill separately.
Instance cross-AZ without LB — InterZone path; use Mode A with path=cross-az.
Public Internet responses — Internet DT-out; watch free-tier cliff.
Cross-zone off — model imbalance and failover — not a savings promise.

Common traps

ELB GB blended with InterZone — Blending ELB cross-zone GB with EC2 InterZone / cross-AZ on one chart hides two meters. Map both in the Cost Explorer decoder.
LCU/NLCU ignored — Optimizing only DT while ignoring ALB LCU / NLB NLCU hours understates the LB path. Hours and processed-bytes dimensions stay on separate lines.
ALB ≠ NLB SKUs — Assuming NLB pricing matches ALB (or vice versa) invents rates. Verify cross-zone rows on dated Elastic Load Balancing pricing.
Cross-zone off = savings — Turning cross-zone off can drop the ELB cross-zone line toward zero but pins clients to one AZ — imbalance and failover risk are not a savings guarantee.
Internet DT-out folded into cross-zone — Client downloads are Internet DT-out (watch free-tier cliff); east-west via the LB is a different path template. No guaranteed savings from either alone.

FinOps checklist

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

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.
Line Internet DT-out × 5,000 GB — rate Unknown (watch free-tier cliff).
Line ALB LCU-hours — rate Unknown.
Line ELB cross-zone DT × 1,200 GB — rate Unknown (verify ALB pricing row).
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 line	Volume	Unit rate
1	Internet DT-out (client downloads)	5,000 GB	Unknown $/GB
2	ALB LCU-hours	monthly LCUs	Unknown $/LCU-hour
3	ELB cross-zone data transfer	1,200 GB	Unknown $/GB
4	Instance InterZone (if any)	separate export	Unknown $/GB

Second educational stack (cross-zone on vs off): same 5,000 GB client Internet DT-out and the same target herd across three AZs. With cross-zone on, estimate 1,200 GB ELB cross-zone DT as above. With cross-zone off, that ELB cross-zone line drops toward zero — but clients pin to the AZ their DNS/tuple lands on, so one AZ can run hot while others idle, and any instance-to-instance mesh remains a separate InterZone / cross-AZ meter. Re-run Mode A (?path=cross-az) only for the measured cross-zone GB; do not invent savings from the off state. Knit labels in the Cost Explorer decoder (ELB/ALB vs InterZone vs Internet) before blending. Synthetic only — rates Unknown; no savings guarantee.

Worked-estimate sensitivity (educational)

Hold the 5,000 GB client Internet DT-out baseline and walk three ELB / InterZone runs. LCU, cross-zone, InterZone, and Internet $/GB cells stay Unknown until dated ELB / EC2 cites — literacy arithmetic, not a quote.

Run A — Cross-zone on: 5,000 GB Internet DT-out + estimated 1,200 GB ELB cross-zone + ALB LCU-hours. Open Mode A (?path=elb-xz&gb=1200). Keep instance InterZone off this line unless CE shows it.
Run B — Cross-zone off twin: same 5,000 GB Internet DT-out and target herd across three AZs; ELB cross-zone → ~0, but AZ affinity can hot-spot one AZ. Re-run Mode A only for measured east-west GB; do not invent savings from the off state.
Run C — InterZone mesh sibling: add a separate instance-to-instance cross-AZ mesh (e.g. 800 GB InterZone) beside the LB path. Model with Mode A (?path=cross-az); knit labels in the CE decoder and cross-AZ vs cross-region spoke.

Sensitivity runs — Unknown rates (educational)
Run	What changes	Meters to keep visible	Unit rates
A	Cross-zone on · 1,200 GB ELB XZ	Internet DT-out · LCU · ELB cross-zone	Unknown
B	Cross-zone off twin	Internet DT-out · LCU · AZ imbalance (no invent)	Unknown
C	InterZone mesh sibling (+800 GB)	ELB lines · separate InterZone · CE labels	Unknown

Cross-read NAT vs IGW, AWS path checklist, cross-AZ vs cross-region, and methodology. Badge every unverified rate Unknown until verified. No savings guarantee.

Open calculator Mode A (elb-xz) Mode A · cross-AZ sibling 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. Map ELB/ALB cross-zone GB beside InterZone and Internet DT-out in the Cost Explorer decoder before blending — see also cross-AZ vs cross-region and glossary: ELB cross-zone.

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.

What changes when I turn cross-zone load balancing off?

The ELB cross-zone data-transfer line may shrink, but AZ imbalance and client pin-risk rise. Instance InterZone chatter does not automatically disappear. Model on vs off as two stacks with the CE decoder; PipeToll never guarantees savings.

Trademarks: Amazon Web Services, AWS, Microsoft Azure, Google Cloud Platform, GCP, and Cloudflare are trademarks of their respective owners. PipeToll (Ameti One LLC) is not affiliated with, endorsed by, or sponsored by those companies. Educational comparisons may be outdated — verify current rates with each provider.