1.5.3.1. 模块元参数

在 Terraform 0.13 之前，模块在使用上存在一些限制。例如我们通过模块来创建 EC2 主机，可以这样：

module "ec2_instance" {
  source  = "terraform-aws-modules/ec2-instance/aws"
  version = "~> 3.0"

  name = "single-instance"

  ami                    = "ami-ebd02392"
  instance_type          = "t2.micro"
  key_name               = "user1"
  monitoring             = true
  vpc_security_group_ids = ["sg-12345678"]
  subnet_id              = "subnet-eddcdzz4"

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

如果我们要创建两台这样的主机怎么办？在 Terraform 0.13 之前的版本中，由于 Module 不支持元参数，所以我们只能手动拷贝模块代码：

module "ec2_instance_0" {
  source  = "terraform-aws-modules/ec2-instance/aws"
  version = "~> 3.0"

  name = "single-instance-0"

  ami                    = "ami-ebd02392"
  instance_type          = "t2.micro"
  key_name               = "user1"
  monitoring             = true
  vpc_security_group_ids = ["sg-12345678"]
  subnet_id              = "subnet-eddcdzz4"

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

module "ec2_instance_1" {
  source  = "terraform-aws-modules/ec2-instance/aws"
  version = "~> 3.0"

  name = "single-instance-1"

  ami                    = "ami-ebd02392"
  instance_type          = "t2.micro"
  key_name               = "user1"
  monitoring             = true
  vpc_security_group_ids = ["sg-12345678"]
  subnet_id              = "subnet-eddcdzz4"

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

自从 Terraform 0.13 开始，模块也像资源一样，支持count、for_each、depends_on三种元参数。比如我们可以这样：

module "ec2_instance" {
  count = 2
  source  = "terraform-aws-modules/ec2-instance/aws"
  version = "~> 3.0"

  name = "single-instance-${count.index}"

  ami                    = "ami-ebd02392"
  instance_type          = "t2.micro"
  key_name               = "user1"
  monitoring             = true
  vpc_security_group_ids = ["sg-12345678"]
  subnet_id              = "subnet-eddcdzz4"

  tags = {
    Terraform   = "true"
    Environment = "dev"
  }
}

要注意的是 Terraform 0.13 之后在模块上声明depends_on，列表中也可以传入另一个模块。声明depends_on的模块中的所有资源的创建都会发生在被依赖的模块中所有资源创建完成之后。