Day-10: Conditional expressions, Dynamic blocks, Splat expressions in terraform

Source: Dev.to

Conditional Expressions

Conditional expressions in Terraform allow you to choose between two values based on a condition. The syntax is condition ? true_value : false_value. This is useful for setting resource attributes based on variable values or other conditions.

• Choose instances based on the environment (dev/prod)
• Enable monitoring based on the configurations
• Select different AMIs based on region

Example

// main.tf
resource "aws_instance" "instance" {
  ami           = "ami-0fa3fe0fa7920f68e"
  region        = "us-east-1"
  instance_type = var.environment == "dev" ? "t3.micro" : "t3.small"
  count         = var.instance_count

  tags = var.tags
}

// variables.tf
variable "environment" {
  type    = string
  default = "dev"
}

Splat Expressions

Splat expressions allow you to extract multiple values from a list of objects. The syntax is resource_type.resource_name[*].attribute. This is useful for retrieving attributes from multiple instances of a resource.

Example

// main.tf
resource "aws_instance" "instance" {
  ami           = "ami-0fa3fe0fa7920f68e"
  region        = "us-east-1"
  instance_type = var.environment == "dev" ? "t3.micro" : "t3.small"
  count         = var.instance_count

  tags = var.tags
}

// splat expression example in Terraform
output "instance_ids" {
  value = aws_instance.instance[*].id
}

Dynamic Blocks

Dynamic blocks in Terraform allow you to generate multiple nested blocks within a resource based on a list or map variable. The syntax is:

dynamic "block_name" {
  for_each = var.list_variable
  content {
    # block attributes
  }
}

This is useful for creating multiple similar configurations without duplicating code.

Example

// variables.tf
variable "ingress_values" {
  type = list(object({
    from_port   = number
    to_port     = number
    protocol    = string
    cidr_blocks = list(string)
  }))

  default = [
    {
      from_port   = 80
      to_port     = 80
      protocol    = "tcp"
      cidr_blocks = ["0.0.0.0/0"]
    },
    {
      from_port   = 443
      to_port     = 443
      protocol    = "tcp"
      cidr_blocks = ["0.0.0.0/0"]
    }
  ]
}

// main.tf
resource "aws_security_group" "security_group" {
  name = "sg"

  dynamic "ingress" {
    for_each = var.ingress_values
    content {
      from_port   = ingress.value.from_port
      to_port     = ingress.value.to_port
      protocol    = ingress.value.protocol
      cidr_blocks = ingress.value.cidr_blocks
    }
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

By using conditional expressions, splat expressions, and dynamic blocks, you can create more flexible, reusable, and maintainable Terraform configurations.

@piyushsachdeva