1 min lesson
IP planning so growth doesn't corner you
Show why this lesson detail matters: "Leading with CIDR strategy signals you have operated at scale, where renumbering is the scar everyone has."
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IP planning so growth doesn't corner youthe decision you can't easily undo
Pods on the EKS VPC CNI each consume a real VPC IP, so a busy cluster burns through address space fast. Plan CIDRs with that appetite in mind and reserve non-overlapping ranges per region and per account up front. Overlapping CIDRs are the thing that quietly blocks peering and Transit Gateway later and the fix is a renumbering project nobody wants.
When asked to design a VPC, draw the address plan before the boxes: "I'd give each region a /16 from a non-overlapping parent range, split into per-AZ public and private /20s and reserve a second /16 per region for CNI growth." Leading with CIDR strategy signals you have operated at scale, where renumbering is the scar everyone has.
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Optional practice
Practice: IP planning so growth doesn't corner you
QYou have two private subnets in different AZs. One can reach the internet to pull container images; the other times out on every outbound call. Both have the same security groups. What's the most likely cause?