How to fix Error: Duplicate resource in Terraform

# Search for all instances of the duplicated resource
grep -r "resource \"aws_instance\" \"example\"" .

# Or for a specific resource type
grep -r "aws_instance" . | grep "example"

# If you have two identical blocks:
resource "aws_instance" "example" {
  # configuration A
}

resource "aws_instance" "example" {
  # configuration B (duplicate - DELETE THIS ONE)
}

# Rename one instead:
resource "aws_instance" "example" {
  # configuration A
}

resource "aws_instance" "example_secondary" {
  # configuration B (RENAMED)
}

# Problem: Both module instances create aws_instance "default"
module "web" {
  source = "./modules/instance"
}

module "db" {
  source = "./modules/instance"  # Same module, same resource names!
}

# Solution 1: Use different module names (not ideal)
module "web_instance" {
  source = "./modules/instance"
}

module "db_instance" {
  source = "./modules/instance"
}

# Solution 2: Pass a variable for unique naming
module "web" {
  source = "./modules/instance"
  instance_name = "web"
}

module "db" {
  source = "./modules/instance"
  instance_name = "db"
}

# Then in module, construct the name:
resource "aws_instance" "server" {
  tags = {
    Name = "${var.instance_name}-server"
  }
}

# Problem: for_each with duplicate keys
locals {
  servers = {
    web = { instance_type = "t2.micro" }
    db  = { instance_type = "t2.small" }
    web = { instance_type = "t2.medium" }  # DUPLICATE KEY "web"!
  }
}

resource "aws_instance" "servers" {
  for_each      = local.servers
  instance_type = each.value.instance_type
}

# Solution: Rename to have unique keys
locals {
  servers = {
    web    = { instance_type = "t2.micro" }
    db     = { instance_type = "t2.small" }
    web_v2 = { instance_type = "t2.medium" }  # RENAMED
  }
}

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