How to use Terraform for multi-region deployments?

Question

Accepted Answer

**Multi-region Terraform** — deploy to multiple regions with shared code.

**Module-based approach:**
```hcl
# modules/region/main.tf
resource "aws_vpc" "main" {
  cidr_block = var.vpc_cidr
  tags = {
    Name = "${var.region}-vpc"
    Region = var.region
  }
}

resource "aws_instance" "web" {
  ami           = var.ami_id
  instance_type = var.instance_type
  subnet_id     = aws_subnet.main.id
}

variable "region" { type = string }
variable "vpc_cidr" { type = string }
variable "ami_id" { type = string }
variable "instance_type" { type = string }

output "vpc_id" { value = aws_vpc.main.id }
output "instance_ip" { value = aws_instance.web.public_ip }
```

**Root module (for_each per region):**
```hcl
# main.tf
variable "regions" {
  default = {
    us-east-1 = {
      vpc_cidr     = "10.0.0.0/16"
      instance_type = "t3.micro"
    }
    eu-west-1 = {
      vpc_cidr     = "10.1.0.0/16"
      instance_type = "t3.small"
    }
  }
}

module "region" {
  source   = "./modules/region"
  for_each = var.regions

region        = each.key
  vpc_cidr      = each.value.vpc_cidr
  instance_type = each.value.instance_type
  ami_id        = data.aws_ami.amazon_linux[each.key].id
}

provider "aws" {
  alias  = "us_east_1"
  region = "us-east-1"
}

data "aws_ami" "amazon_linux" {
  for_each = var.regions
  provider = aws.us_east_1
  most_recent = true
  owners      = ["amazon"]
  filter {
    name   = "name"
    values = ["amzn2-ami-hvm-*-x86_64-gp2"]
  }
}
```

**Global resources (Route53):**
```hcl
resource "aws_route53_record" "failover" {
  for_each = module.region
  zone_id  = aws_route53_zone.main.zone_id
  name     = "myapp.${each.key}.example.com"
  type     = "A"
  ttl      = 60
  records  = [each.value.instance_ip]
}
```

**Terragrunt approach:** Separate folders for each region with shared modules.

DevOps: How to use Terraform for multi-region deployments?