Using Date, Time, and Network Functions

1. Using timestamp Function

Function	Description	Example
timestamp()	Returns the current date and time in RFC3339 format	`2026-01-25T14:30:00Z`

Example: Using timestamp in resource naming

resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"
  tags = {
    Name = "web-server-${timestamp()}"
  }
}

2. Using formatdate Function

Argument	Description	Example
format	Format string specifying the date/time layout	`"YYYY-MM-DD"`
timestamp	Input timestamp to format (optional, defaults to current time)	`"2024-01-01T00:00:00Z"`

Example: Formatting Current Date

output "current_date" {
  value = formatdate("YYYY-MM-DD", timestamp())
}

Example: Formatting Specific Timestamp

output "formatted_date" {
  value = formatdate("DD/MM/YYYY", "2024-07-15T10:30:00Z")
}

Note: The formatdate function uses the Luxon parsing tokens for format strings.

3. Using timeadd Function

Argument	Description	Example
time	The input time string in RFC3339 format	`"2024-01-01T00:00:00Z"`
duration	Duration to add, in Terraform duration format	`"1h"`
result	Output time string in RFC3339 format	`"2024-01-01T01:00:00Z"`

Example: Adding one hour to a timestamp

timeadd("2024-01-01T00:00:00Z", "1h")

Example: Adding 30 minutes to a timestamp

timeadd("2024-01-01T00:00:00Z", "30m")

4. Using timecmp Function

Function	Signature	Description	Return Type
timecmp	`timecmp(time1, time2)`	Compares two time values and returns an integer indicating their relative order.	`number`

Example: Comparing Time Values

locals {
  time1 = "2025-04-01T10:00:00Z"
  time2 = "2025-04-01T12:00:00Z"
  comparison = timecmp(time1, time2)
}

Note: The timecmp function returns 0 if the times are equal, a negative number if time1 is earlier than time2, and a positive number if time1 is later than time2.

5. Using plantimestamp Function

Property	Description	Example
plantimestamp	Generates a timestamp in RFC3339 format based on the current date and time	`plantimestamp()`

Example: Using plantimestamp in a resource

resource "aws_instance" "example" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"

  tags = {
    CreatedAt = plantimestamp()
  }
}

Note: The plantimestamp() function is useful for tagging resources with creation timestamps. It returns a string in RFC3339 format (e.g., 2025-04-05T14:30:00Z).

6. Using cidrhost Function

Argument	Description	Example
cidrhost()	Generates an IP address within a CIDR block	`cidrhost("10.0.0.0/16", 5)`

Example: Generate IP Address from CIDR Block

resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"

  # Assigning an IP address from a subnet
  private_ip = cidrhost("10.0.1.0/24", 10)
}

Note: The cidrhost function takes a subnet and a host number, returning the IP address at that position in the subnet.

7. Using cidrsubnet Function

Argument	Description	Example
cidrsubnet()	Generates a subnet within a given CIDR block	`cidrsubnet("10.0.0.0/16", 4, 5)`

Example: Basic Usage

resource "aws_subnet" "example" {
  vpc_id     = aws_vpc.example.id
  cidr_block = cidrsubnet(aws_vpc.example.cidr_block, 4, 5)
}

Example: Subnetting with Different Prefix Lengths

output "subnet_cidr" {
  value = cidrsubnet("192.168.0.0/16", 8, 10)
}

Note: The function takes a base CIDR block, a prefix length increment, and a subnet number to calculate the new subnet.

8. Using cidrnetmask Function

Function	Signature	Description	Example
cidrnetmask	`cidrnetmask(string)`	Returns the netmask for a CIDR block.	`cidrnetmask("192.168.1.0/24") => "255.255.255.0"`

Example: Using cidrnetmask in a Network Configuration

resource "aws_subnet" "example" {
  vpc_id = aws_vpc.example.id
  cidr_block = "10.0.1.0/24"
  availability_zone = "us-west-2a"
  map_public_ip_on_launch = false
}

output "subnet_netmask" {
  value = cidrnetmask(aws_subnet.example.cidr_block)
}

9. Using cidrsubnetloop Function

The cidrsubnetloop function in Terraform is used to generate a list of CIDR subnets by looping through a specified range and applying subnetting logic. It is particularly useful when you need to create multiple subnets with a consistent pattern, such as in a VPC or network configuration.

Argument	Type	Description
base_cidr_block	string	The base CIDR block from which subnets will be derived.
new_bits	number	The number of additional bits to add to the subnet mask for each generated subnet.
count	number	The total number of subnets to generate.

Example: Using cidrsubnetloop to Generate Subnets

output "subnet_cidrs" {
  value = cidrsubnetloop("10.0.0.0/16", 4, 3)
}

This example generates three subnets from the base CIDR block 10.0.0.0/16, each with an additional 4 bits in the subnet mask, resulting in subnets like 10.0.0.0/20, 10.0.16.0/20, and 10.0.32.0/20.

Note: The cidrsubnetloop function is available in Terraform v1.6 and later.

10. Using cidrcontains Function

The cidrcontains function in Terraform checks whether a given IP address or subnet is contained within another subnet.

Argument	Type	Description
cidr	`string`	The parent CIDR block to check against (e.g., `"10.0.0.0/8"`)
ip	`string`	The IP address or subnet to check for containment (e.g., `"10.0.1.0/24"`)

Example: Checking if an IP is within a subnet

output "ip_in_subnet" {
  value = cidrcontains("10.0.0.0/8", "10.0.1.0/24")
}

Example: Checking if a subnet is contained within another

output "subnet_in_subnet" {
  value = cidrcontains("192.168.0.0/16", "192.168.1.0/24")
}

Note: The function returns true if the second argument (IP or subnet) is fully contained within the first argument (CIDR block). It supports both IPv4 and IPv6 subnets.