feat: (IAC-367) Allow Ability To Specify Which Availability Zones the Subnets Get Created In

[jarpat]

Changes

Allows users the ability to specify which AZs that the subnet gets created in with the new subnet_azs variable.

Similar to the existing subnets the map lets to set the name of the subnet along with zones will be used during creation

subnet_azs = {
  "private"       : ["us-east-2c"],
  "control_plane" : ["us-east-2c", "us-east-2b"],
  "public"        : ["us-east-2a", "us-east-2b"],
  "database"      : ["us-east-2a", "us-east-2b"]
}

So if your defined subnets as so in your .tfvars

{
    "private" : ["192.168.0.0/18"], 
    "control_plane" : ["192.168.130.0/28", "192.168.130.16/28"],
    "public" : ["192.168.129.0/25", "192.168.129.128/25"],
    "database" : ["192.168.128.0/25", "192.168.128.128/25"]
}

for "control_plane" : ["192.168.130.0/28", "192.168.130.16/28"], the first subnet will be created in us-east-2c and the second in us-east-2b

This variable is entirely optional, and if not defined the code will perform a lookup to populate the zones just like the behavior in viya4-iac-aws:7.2.1 and prior. If entire keys are not defined, the lookup will be used to populate those.

Tests

Scenario	Provider	Summary	K8s Version	Order	Cadence
1	AWS	OOTB, subnet_azs not defined	v1.26.10-eks-4f4795d	******	fast:2020
2	AWS	OOTB, all keys in subnet_azs customized	v1.26.10-eks-4f4795d	******	fast:2020
3	AWS	OOTB, partial keys in subnet_azs defined	v1.26.10-eks-4f4795d	******	fast:2020

Validation Scenarios

In all cases subnet was left as the default value: https://github.com/sassoftware/viya4-iac-aws/blob/staging/variables.tf#L371

Scenario	Summary	Behavior
1	subnet_azs not defined, defaults to {}	Valid, no error message
2	subnet_azs fully defined, correct entries per each key	Valid, no error message
3	subnet_azs defined, private key omitted	Valid, no error message
4	subnet_azs defined, control_plane key omitted	Valid, no error message
5	subnet_azs defined, database key not enough entries	Invalid, error message thrown
6	subnet_azs defined, public key not enough entries	Invalid, error message thrown
7	subnet_azs defined, control_plane key extra entries	Valid, no error message

[jarpat]

@dhoucgitter good catch on the vars/docs, applied those suggestions.

[thpang]

I am ok with the update here as long as we check to ensure the same number of elements for each subnet match the cidr and azs. We can at least ensure they have matching items.

[jarpat]

I am ok with the update here as long as we check to ensure the same number of elements for each subnet match the cidr and azs. We can at least ensure they have matching items.

@thpang see latest commit, validation added.

[thpang]

LGTM

[jarpat]

Tests ran fine, did a minor doc update as well for the variable. Merging.