Comparison
Cross-zone traffic costvsEgress charge
Cross-zone traffic cost
spreading replicas across zones for resilience quietly added a per-gigabyte charge to every internal call between them.
The charge for data moving between availability zones inside a region, applied in both directions on many providers. It is invisible in architecture diagrams and material for chatty services, replicated databases and meshes that route without regard to topology. Zone-aware routing — preferring a local endpoint when one is healthy — is the standard mitigation, and it trades some balance for a real saving.
Full entry →Egress charge
the compute was predictable and the surprise on the invoice was gigabytes leaving the provider, at a rate nobody had modelled.
The cost of moving data out of a cloud provider to the internet or to another provider. It is asymmetric — inbound is typically free — which is what makes it both a cost surprise and a genuine lock-in mechanism, since leaving means paying to take your data with you. It also drives architecture: a caching layer or a delivery network in front of heavy outbound traffic is frequently a cost decision rather than a latency one.
Full entry →