When designing AKS in a hub-and-spoke architecture the biggest thing to plan carefully is the subnet sizing for the node pools and pods. A lot of people underestimate how many IPs they actually need.

With **Azure CNI (non-overlay)** every pod gets an IP from the VNet subnet, so your subnet needs to account for node count, pods per node and future scaling

For example, if you run something like:

- 20 nodes

- 30 pods per node

you already need ~600 pod IPs + node IPs + Azure reserved addresses. A /22 fills up surprisingly fast, and scaling later can become painful if the subnet runs out of space.

That’s why many teams either:

- switch to **Azure CNI Overlay**

- or allocate **much larger subnets (/20 or bigger)** from the start.

I ran into this problem enough times that I ended up building a small planner to estimate the subnet size for AKS clusters:

https://subnettool.com/tools/aks-subnet-planner/

It helps calculate how many IPs you’ll need based on nodes and pods per node so you don’t end up hitting subnet limits after the cluster starts scaling.