Cloud cost
Data egress
The fee a cloud provider charges for data leaving its network, including (on most providers) transfer between availability zones.
Last updated
Definition
Data egress is billed per gigabyte for traffic leaving the provider's network toward the public internet, another cloud, or (on most providers) even a different availability zone within the same region. It's one of the least visible line items on a bill because it scales with application behavior. A chatty microservice architecture or an unoptimized data pipeline can rack up meaningful egress with no single obvious cause.
Cross-AZ transfer specifically catches teams off guard: traffic that never leaves the provider's network still crosses a per-GB charge the moment it crosses an availability-zone boundary, which is easy to miss when architecting for high availability across zones.
Where it shows up
Data egress appears on an AWS bill under DataTransfer usage types, split by direction: out to the internet, to another region, or across Availability Zones. Cost Explorer's default Service grouping often folds these into a broader EC2-Other bucket, so switching to Usage type is what makes the charge visible on its own.
What makes it expensive
Splitting a chatty service across Availability Zones buys high availability and, alongside it, a per-gigabyte bill nobody priced. That line bills both legs of a move, so one service spread across zones can double the transfer charge for the same request volume. If DataTransfer-Regional-Bytes climbs in step with request volume rather than with any capacity change you made, the architecture is the cause, not the traffic.
Related
More in Cloud cost
- Committed use discount (CUD)
- Reserved instance (RI)
- Savings plan (SP)
- On-demand vs. spot instances
- Amortized, blended, and unblended cost
- Billed vs. effective vs. list vs. contracted cost
- Rightsizing
- Idle and orphaned resources
- Storage class
- Lifecycle policy
- Incremental snapshot
- Allocatable capacity
- Requests vs. limits
- Cluster idle
- Workload idle
- Bin packing
- Cost allocation tags
- Tag coverage
- Unallocated spend
- Showback vs. chargeback
- Unit economics
- RI/SP coverage and utilization
- Observability tax
- Metric cardinality
- High-water-mark billing
- Log ingest vs. index
- Snowflake credit
- Auto-suspend / resume minimum
- BigQuery slot
- Bytes scanned & partition pruning
- Time Travel & Fail-safe
Connect a provider. See one number.
Connect your first provider and CostMon normalizes it alongside everything else you run. Your team gets one number everyone can check.