Almost every cost estimate written before a workload is deployed accounts for compute and storage. Almost none accounts for the traffic. On the hyperscaler platforms, traffic leaving the network is frequently the largest single surprise on the bill.
What counts as egress
The general rule across providers is that data flowing in is free and data flowing out is billed. “Out” is broader than most people assume:
- Responses to your users — every page, image, API payload and video byte.
- Traffic to another cloud provider, or to your own office.
- Traffic between regions of the same provider.
- On some platforms, traffic between availability zones inside a single region.
- Backups written to somewhere outside the provider’s network.
Traffic within a single zone, over private addresses, is normally free or close to it. That single fact drives a lot of good cloud architecture.
Two different billing models
Providers in this catalogue fall into two camps, and the difference is structural rather than cosmetic:
- Metered from the first byte. Typical of the hyperscalers. Every gigabyte out is priced, often on a tiered scale, and often differently per region and per destination.
- Pooled allowance per plan. Typical of the VPS-oriented providers. Each server includes a monthly transfer allowance, allowances pool across the account, and you pay only for overage.
For a bandwidth-heavy workload the second model is dramatically more predictable, which is why it is often the deciding factor rather than the CPU price. AWS vs Hetzner and AWS vs DigitalOcean both come down to this more often than to raw compute.
Where egress hides
- Cross-zone database replicas. Every write is replicated, and on some platforms every replicated byte crosses a billed boundary.
- NAT gateways. Processing charges apply per gigabyte in addition to the transfer itself, and everything in a private subnet goes through one.
- Logs and metrics shipped off-platform. Continuous, unglamorous, and easy to forget entirely.
- Object storage read by an external service. Storage is cheap; reading it from outside the network repeatedly is not.
- Container image pulls. A CI pipeline that pulls large images on every build is moving real volume.
Reducing it without redesigning everything
- Put a CDN in front of anything static. The CDN absorbs repeat reads, and its origin-fetch traffic is a fraction of what the origin would otherwise serve.
- Keep chatty components in the same zone. Application and database in one zone, replicated across zones only where availability genuinely requires it.
- Compress responses. Egress is billed in bytes, and gzip or brotli on JSON and HTML is close to free.
- Use private endpoints. Traffic to managed services over the provider’s private network usually avoids the public path and its charge.
- Keep backups inside the provider first, then copy off-platform on a schedule rather than continuously.
Estimating before you deploy
A workable estimate needs only three numbers: average response size, requests per month, and a multiplier for retries, prefetching and bots. Bots are not a rounding error — for a public site they can be a large fraction of all traffic.
Once you have a monthly gigabyte figure, compare it against both billing models. That comparison, more than any CPU benchmark, tells you which provider is cheaper for your workload. Set a budget alert at the number you expect, so the first month tells you whether the estimate was right.
Where to go next
- How cloud billing works, and how bills get out of hand
- Cutting cloud costs without downtime
- Block, object and file storage
Questions
Frequently asked
Is incoming traffic to a cloud server free?
Ingress is free or nominal on every provider in this catalogue. It is outbound traffic that is billed, which is why upload-heavy workloads are cheap to host and download-heavy ones are not.
Does traffic between two of my own servers cost money?
It depends where they are. Within a single zone over private addresses it is normally free. Across zones or regions it is usually billed, even though both machines are yours.
Do VPS providers charge for bandwidth?
Most include a monthly transfer allowance with each plan and bill only for what exceeds it. That makes costs far more predictable than per-gigabyte metering for traffic-heavy sites.