Improve subnet CIDR calculation (#29)

modules/terraform-cdp-aws-pre-reqs/main.tf

@@ -26,6 +26,8 @@ module "aws_cdp_vpc" {
   env_prefix                 = var.env_prefix
   tags                       = local.env_tags
 
+  private_cidr_range = var.private_cidr_range
+  public_cidr_range  = var.public_cidr_range
 }
 
 # ------- Security Groups -------

modules/terraform-cdp-aws-pre-reqs/modules/vpc/defaults.tf

@@ -25,4 +25,10 @@ locals {
     public  = (var.deployment_template == "private") ? (var.private_network_extensions ? 1 : 0) : length(local.zones_in_region)
     private = (var.deployment_template == "public") ? 0 : length(local.zones_in_region)
   }
+
+  # Extract the VPC CIDR range from the user-provided CIDR
+  vpc_cidr_range = split("/", var.vpc_cidr)[1]
+
+  # Calculate the first suitable CIDR range for public subnets after private subnets have been allocated (normalize the offset, expressed as a multiplier of public subnet ranges)
+  public_subnet_offset = ceil(local.subnets_required.private * pow(2, 32 - var.private_cidr_range) / pow(2, 32 - var.public_cidr_range))
 }

modules/terraform-cdp-aws-pre-reqs/modules/vpc/main.tf

@@ -23,7 +23,7 @@ module "cdp_vpc" {
   private_subnets = (local.subnets_required.private == 0 ?
     [] :
     [
-      for i in range(local.subnets_required.private) : cidrsubnet(var.vpc_cidr, ceil(log(local.subnets_required.total, 2)), local.subnets_required.public + i)
+      for i in range(local.subnets_required.private) : cidrsubnet(var.vpc_cidr, var.private_cidr_range - local.vpc_cidr_range, i)
     ]
   )
   private_subnet_tags = {
@@ -33,7 +33,7 @@ module "cdp_vpc" {
   public_subnets = (local.subnets_required.public == 0 ?
     [] :
     [
-      for i in range(local.subnets_required.public) : cidrsubnet(var.vpc_cidr, ceil(log(local.subnets_required.total, 2)), i)
+      for i in range(local.subnets_required.public) : cidrsubnet(var.vpc_cidr, var.public_cidr_range - local.vpc_cidr_range, i + local.public_subnet_offset)
     ]
   )
 

modules/terraform-cdp-aws-pre-reqs/modules/vpc/variables.tf

@@ -18,6 +18,16 @@ variable "vpc_cidr" {
 
 }
 
+variable "private_cidr_range" {
+  type        = number
+  description = "Size of each private subnet"
+}
+
+variable "public_cidr_range" {
+  type        = number
+  description = "Size of each public subnet"
+}
+
 variable "tags" {
   type        = map(any)
   description = "Tags applied to provised resources"
@@ -45,4 +55,6 @@ variable "private_network_extensions" {
 
   description = "Enable creation of resources for connectivity to CDP Control Plane (public subnet and NAT Gateway) for Private Deployment. Only relevant for private deployment template."
 
-}
+}
+
+

modules/terraform-cdp-aws-pre-reqs/variables.tf

@@ -90,11 +90,25 @@ variable "create_vpc" {
 
 variable "vpc_cidr" {
   type        = string
-  description = "VPC CIDR Block"
+  description = "VPC CIDR Block. Required if create_vpc is true."
 
   default = "10.10.0.0/16"
 }
 
+variable "private_cidr_range" {
+  type        = number
+  description = "Size of each private subnet. Required if create_vpc is true. Number of subnets will be automatically selected to match on the number of Availability Zones in the selected AWS region. (Depending on the selected deployment pattern, one subnet will be created per region.)"
+
+  default = 19
+}
+
+variable "public_cidr_range" {
+  type        = number
+  description = "Size of each public subnet. Required if create_vpc is true. Number of subnets will be automatically selected to match on the number of Availability Zones in the selected AWS region. (Depending on the selected deployment pattern, one subnet will be created per region.)"
+
+  default = 24
+}
+
 variable "private_network_extensions" {
   type = bool
 

modules/terraform-cdp-azure-pre-reqs/main.tf

@@ -39,6 +39,10 @@ module "azure_cdp_vnet" {
 
   env_prefix = var.env_prefix
   tags       = local.env_tags
+
+  cdp_subnet_range     = var.cdp_subnet_range
+  gateway_subnet_range = var.gateway_subnet_range
+
 }
 
 

modules/terraform-cdp-azure-pre-reqs/modules/vnet/defaults.tf

@@ -23,12 +23,19 @@ locals {
     # cidr            = cidrsubnet(var.vnet_cidr, ceil(log(var.subnet_count, 2)), idx)
   }
 
+  # Extract the VNet CIDR range from the user-provided CIDR
+  vnet_cidr_range = split("/", var.vnet_cidr)[1]
+
+  # Calculate the first suitable CIDR range for public subnets after private subnets have been allocated (normalize the offset, expressed as a multiplier of gateway subnet ranges)
+  gateway_subnet_offset = ceil(local.subnets_required.cdp_subnets * pow(2, 32 - var.cdp_subnet_range) / pow(2, 32 - var.gateway_subnet_range))
+
+
   # Network infrastructure for CDP resources
   cdp_subnets = [
     for idx in range(local.subnets_required.cdp_subnets) :
     {
       name = "${var.env_prefix}-sbnt-${format("%02d", idx + 1)}"
-      cidr = cidrsubnet(var.vnet_cidr, ceil(log(local.subnets_required.total, 2)), idx)
+      cidr = cidrsubnet(var.vnet_cidr, var.cdp_subnet_range - local.vnet_cidr_range, idx)
     }
   ]
 
@@ -37,7 +44,7 @@ locals {
     for idx in range(local.subnets_required.gateway_subnets) :
     {
       name = "${var.env_prefix}-gw-sbnt-${format("%02d", idx + 1)}"
-      cidr = cidrsubnet(var.vnet_cidr, ceil(log(local.subnets_required.total, 2)), local.subnets_required.cdp_subnets + idx)
+      cidr = cidrsubnet(var.vnet_cidr, var.gateway_subnet_range - local.vnet_cidr_range, idx + local.gateway_subnet_offset)
     }
   ]
 

modules/terraform-cdp-azure-pre-reqs/modules/vnet/variables.tf

@@ -40,6 +40,18 @@ variable "vnet_cidr" {
 
 }
 
+variable "cdp_subnet_range" {
+  type        = number
+  description = "Size of each (internal) cluster subnet"
+
+}
+
+variable "gateway_subnet_range" {
+  type        = number
+  description = "Size of each gateway subnet"
+
+}
+
 variable "vnet_region" {
   type        = string
   description = "Region which VNet will be created"

modules/terraform-cdp-azure-pre-reqs/variables.tf

@@ -39,12 +39,6 @@ variable "env_prefix" {
   description = "Shorthand name for the environment. Used in resource descriptions"
 }
 
-# variable "public_key_text" {
-#   type = string
-
-#   description = "SSH Public key string for the nodes of the CDP environment"
-# }
-# ------- CDP Environment Deployment -------
 variable "deployment_template" {
   type = string
 
@@ -89,11 +83,25 @@ variable "vnet_name" {
 
 variable "vnet_cidr" {
   type        = string
-  description = "VNet CIDR Block"
+  description = "VNet CIDR Block. Required if create_vpc is true."
 
   default = "10.10.0.0/16"
 }
 
+variable "cdp_subnet_range" {
+  type        = number
+  description = "Size of each (internal) cluster subnet. Required if create_vpc is true."
+
+  default = 19
+}
+
+variable "gateway_subnet_range" {
+  type        = number
+  description = "Size of each gateway subnet. Required if create_vpc is true."
+
+  default = 24
+}
+
 variable "cdp_resourcegroup_name" {
   type        = string
   description = "Pre-existing Resource Group for CDP environment. Required if create_vnet is false."