Im new on AKS.
When I add a new node to the cluster AKS it reserves 31 IPs from the subnet I have set.
Exist the possibility to reserve only 21 IPs? OR I cannot change it?
if you use Azure CNI networking option for AKS, then azure reserves 30 + 1 ip addresses for each node.
If you want to save ip addresses then there is another option called kubenet, it uses 1 ip address per node.
While creating aks cluster you can specify the kubenet network plugin option via commandline or if you are creating aks cluster via azure portal then the basic option by default uses kubenet plugin.
Note: Kubenet network option is ideal for dev/test environments or simple on-prem poc type apps. For anything scalable, it is recommended to use azure cni network option.
No, its not possible. this is being controlled by the maxpods value on the nodepool. you cannot change it after you've created AKS cluster. Your only option is to recreate AKS cluster.
It takes 31 IPs because the default value is 30 (so 1 IP for each pod) and 1 IP for the worker node itself