Cross-AZ Data Transfer Optimization Opportunity
What does ZopNight detect here?
Accounts moving 100 GB or more between Availability Zones in a region carry a real DataTransfer-Regional-Bytes bill. ZopNight reads the actual Cost Explorer cross-AZ spend and marks 30% as recoverable through topology-aware routing and same-AZ placement, abstaining whenever the billed cross-AZ cost is absent or zero.
Signal and threshold
| Field | Value |
|---|---|
| Rule IDs | RC-065 |
| Category | rightsizing |
| Severity | low |
| Metric | none — pure configuration read |
| Source | eks_cross_az_traffic.go |
Where it applies
The account-level cross-AZ volume and its billed cost
- Metadata cross_az_transfer_gb (JSON number): the account’s intra-region cross-AZ GB transferred over the lookback; applicability gate (≥ crossAZTransferHighGB = 100 GB), fail-closed.
- Metadata cross_az_transfer_cost_usd (JSON number): the real billed cross-AZ dollars (CE UnblendedCost on the intra-region DataTransfer-Regional-Bytes usage types). The monetary basis for the concrete saving; omitted by the producer when CE reports $0 billed cross-AZ, so the rule abstains rather than ship a $0 rec.
Why cross-AZ traffic can shrink but never reach zero
Category is the cost-driven rightsizing. CurrentCostUSD = the real billed cross-AZ line item (cross_az_transfer_cost_usd). SavingsUSD = cross_az_transfer_cost_usd × crossAZReductionFactor (0.30), the conservatively-recoverable share via topology-aware routing / same-AZ placement. Unlike RC-178’s colocate lever (which removes the whole inter-region line item), cross-AZ transfer cannot go to zero (multi-AZ HA inherently requires some cross-AZ traffic), so a conservative reduction factor is applied to the real CE actuals, not to a synthetic $0.01/GB rate and not to a fraction of compute cost. The rule fires with a concrete number when both signals are present and the billed cost is positive; it abstains (returns nil) when the volume is below threshold or the billed cost is absent/zero. The prior per-cluster cross_az_transfer_gb × $0.01 × 2 plan and the older cost × 0.30-of-compute fraction / $0 advisory are all superseded.
Keeping chatty workloads in the same AZ
- In Cost Explorer, group by Usage Type and filter to DataTransfer-Regional-Bytes to size the cross-AZ line item, then check the per-GB rate AWS charges for traffic between Availability Zones
- Enable Kubernetes Topology Aware Routing (Topology Aware Hints) so traffic prefers same-AZ endpoints
- Co-locate chatty workload pairs (app↔cache, app↔DB) in the same AZ where HA allows
- Use service-mesh locality-aware load balancing for cross-service traffic
- Identify the heaviest cross-AZ talkers via VPC flow logs if per-resource attribution is needed