Egress and Traffic Costs: A Bill Breakdown Checklist for Tech Leads

The most commonly underestimated item in a cloud bill is traffic. Unlike instances, it has no single spec or unit price; it accumulates from several billing items and is discovered only when the monthly bill arrives.

1. Separate Four Traffic Categories

• Public egress: data sent from resources to the internet
• Cross-AZ: transfer between availability zones in one region
• Cross-region: replication and calls between regions
• Request counts: object storage, CDN origin fetches, API gateway calls

Each category is billed differently; viewing them as one total hides where waste occurs.

2. Find Three Common Waste Patterns

1. Application and Database in Different Regions

Every query generates cross-region traffic and added latency. Unless disaster recovery requires it, deploy in the same region.

2. Object Storage Read Directly and Frequently

Images and static files served directly raise both request counts and egress. Adding a CDN usually reduces origin fetch ratio and both costs.

3. Uncompressed Cross-Cloud Sync

Full, uncompressed synchronization multiplies transfer volume and cost. Move to incremental sync and evaluate compression gains.

3. How to Check

Export three months of traffic details by resource type, and label each link with destination and purpose. Links without a clear purpose are usually the optimizable ones. Review latency together to avoid trading experience for cost.

4. Verify After Optimization

Observe for two weeks and compare traffic cost with response time on core APIs. If cost falls but latency rises, assess whether the trade is acceptable.