modules/eks-cluster - desired_size value not being picked up by EKS

[zackproser]

A customer asked:

Hi all - we are noticed that when using the modules/eks-cluster, the desired_size value is not getting picked up by EKS

example:
node_group_default_desired_size = ${value0}
managed_node_groups_configurations = { 
  ngroup1 = { 
    desired_size = ${value1} 
    ... ...
  } ... 
}

as shown here:
https://github.com/gruntwork-io/terraform-aws-service-catalog/blob/master/modules/services/eks-cluster/variables.tf#L693-L709

UNLESS:
its the FIRST time running tg apply (initial creation of cluster)
with node_group_default_desired_size set
withOUT desired_size set in group_config(s)
the name(s) of the node_group(s) have changed
WITH desired_size set in group_config(s) under a new name

Is this expected behavior?

[zackproser]

Yes this is expected. The desired size attribute is setup in this manner so that it can avoid inadvertent terraform drift when using with the cluster autoscale. If you are going for a manual scaling system and not using the cluster autoscaler, the recommendation is to set the min_size and max_size to the same value and scale that way.

[zackproser]

Credit for this solution goes to @yorinasub17