Network Log Interpretation and Cost Drill
Explore how to interpret AWS VPC flow logs and boundary logs to diagnose network symptoms such as timeouts and cost spikes. Understand how to differentiate between traffic acceptance, rejections, and missing flows by analyzing log records. Learn to correlate flow logs with load balancer or edge logs to verify request delivery and troubleshoot performance issues. Gain insights into how traffic patterns relate to AWS data transfer costs and operational trade-offs, empowering you to make informed decisions for optimizing network reliability and expenses.
Two different questions come up whenever a network symptom shows up alongside a cost spike: what actually happened to the traffic, and what did that traffic cost?
Flow logs answer the first question narrowly; they’re evidence about traffic that entered an interface and was evaluated, nothing more. Boundary logs, from a load balancer or edge service, answer a second, separate question: whether a request actually reached its destination and how that destination responded. Neither one alone tells the whole story, and the same byte counts that help diagnose a symptom are usually what explain the cost line item too.
Here's what that looks like together. Users report intermittent timeouts, and the same week, the monthly data transfer line item jumps. The only evidence available quickly is a handful of VPC flow log-style records, plus a few load balancer or edge access lines, so the first move is sorting what those logs can actually prove from what they can't.
A flow record's fields do most of the diagnostic work: accept versus reject, source and destination addresses, ports, direction, and byte and packet counts, which approximate volume and chatter. Every symptom groups into one of three buckets from there.
Explicit rejects show up as
REJECTand usually map to security group or NACL rules, missing routes, or ...