Data transfer rarely appears in an architecture diagram, yet it often appears on the bill. The rules are simple in principle and easy to forget in practice.
Where transfer charges come from
Outbound to the internet.: Data leaving the cloud is generally charged beyond any allowance Oracle includes. Check the current terms for your account.
Between regions.: Replication, backups and cross-region reads move data between regions, and that movement is chargeable.
Private connectivity.: A dedicated connection to your data centre has its own port and usage charges, which can make sense at scale but should be justified.
Traffic inside a single region and between resources on the same virtual network is generally the lowest-cost path, so keeping chatty components close together is the first design lever.
Design habits that help
•Keep services that talk to each other in the same region.
•Cache or compress what you send out to users.
•Think twice before replicating everything to a second region. Replicate what recovery genuinely needs.
•Avoid pulling large datasets out of the cloud for analysis that could run next to the data.
Watch for the surprise
Transfer costs are easiest to catch when you can see networking spend by region over time. A sudden rise usually has a single cause, such as a new replication job or a service that started serving more downloads.