Enterprise Cloud Architecture and Migration Strategy Questions

provider "aws" { region = "us-east-1" alias = "central" }
provider "aws" { region = "us-west-2" alias = "target" }

module "network" {
  source        = "../modules/network"
  providers     = { aws = aws.target }
  name_prefix   = "corp-prod"
  account_id    = "123456789012"
  cidr_block    = "10.0.0.0/16"
  tags = local.common_tags
}

module "security" {
  source    = "../modules/security"
  providers = { aws = aws.central }
  org_id    = "corp"
  tags      = local.common_tags
}

variable "side_a" {
  type = object({
    provider = string    # "aws" or "azure"
    name     = string
    cidr     = string
  })
}

variable "side_b" {
  type = object({
    provider = string
    name     = string
    cidr     = string
  })
}

variable "tags" {
  type    = map(string)
  default = {}
}

# AWS VPC (created only when side.provider == "aws")
resource "aws_vpc" "side_a" {
  count      = var.side_a.provider == "aws" ? 1 : 0
  cidr_block = var.side_a.cidr
  tags       = merge(var.tags, { Name = var.side_a.name })
  # provider used is the aws provider passed into module via providers map
}

resource "aws_vpc" "side_b" {
  count      = var.side_b.provider == "aws" ? 1 : 0
  cidr_block = var.side_b.cidr
  tags       = merge(var.tags, { Name = var.side_b.name })
}

# Azure Virtual Network (created only when provider == "azure")
resource "azurerm_virtual_network" "side_a" {
  count               = var.side_a.provider == "azure" ? 1 : 0
  name                = var.side_a.name
  address_space       = [var.side_a.cidr]
  location            = "placeholder-location"
  resource_group_name = "placeholder-rg"
  tags                = var.tags
}

resource "azurerm_virtual_network" "side_b" {
  count               = var.side_b.provider == "azure" ? 1 : 0
  name                = var.side_b.name
  address_space       = [var.side_b.cidr]
  location            = "placeholder-location"
  resource_group_name = "placeholder-rg"
  tags                = var.tags
}

# Cross-cloud peering: example patterns (high-level wrappers)
# For AWS->Azure use Transit Gateway / Virtual Network Gateway (not fully implemented here)
# Use null_resource or cloud-specific resources to wire the two sides: conditional blocks show intent

resource "null_resource" "peering_placeholder" {
  # create only when both sides exist
  count = (var.side_a.provider != var.side_b.provider) ? 1 : 0
  triggers = {
    side_a = jsonencode(var.side_a)
    side_b = jsonencode(var.side_b)
  }
  # In real implementation: call aws_dx_gateway_attachment / azurerm_virtual_network_peering equivalents
}

output "side_a_network_id" {
  value = coalesce(
    try(aws_vpc.side_a[0].id, null),
    try(azurerm_virtual_network.side_a[0].id, null)
  )
}

output "side_b_network_id" {
  value = coalesce(
    try(aws_vpc.side_b[0].id, null),
    try(azurerm_virtual_network.side_b[0].id, null)
  )
}

output "peering_placeholder_id" {
  value = try(null_resource.peering_placeholder[0].id, "")
}

provider "aws" {
  alias  = "acct1"
  region = "us-west-2"
  # creds...
}

provider "aws" {
  alias  = "acct2"
  region = "us-east-1"
}

provider "azurerm" {
  alias           = "east"
  features        = {}
  subscription_id = "sub-xxxxx"
}

module "multicloud_net" {
  source = "./modules/vnet-peering"

  # pass provider instances so resources inside module use them
  providers = {
    aws      = aws.acct1      # module aws references will use this provider
    azurerm  = azurerm.east   # module azurerm references will use this provider
  }

  side_a = {
    provider = "aws"
    name     = "vpc-a"
    cidr     = "10.0.0.0/16"
  }

  side_b = {
    provider = "azure"
    name     = "vnet-b"
    cidr     = "10.1.0.0/16"
  }

  tags = { Owner = "network-team" }
}