Terraform – FotD – pow()

This is part of an ongoing series of posts documenting the built-in interpolation functions in Terraform. For more information, check out the beginning post. In this post I am going to cover the pow() function. The example file is on GitHub here.

What is it?

Function name: pow(base,exponent)

Returns: Takes a base value and raises it by the exponent

Example:

# Returns 8
output "pow_output" {
  value = "${pow("2","3")}"
}

Example file:

##############################################
# Function: pow
##############################################
##############################################
# Variables
##############################################
variable "base" {}

variable "exp" {}


##############################################
# Resources
##############################################

##############################################
# Outputs
##############################################
output "pow_output" {
  value = "${pow(var.base, var.expZ)}"
}

Run the following from the pow folder to get example output for a number of different cases:

#Basic functionality
terraform apply -var 'base=2' -var 'exp=3'
terraform apply -var 'base=-1' -var 'exp=3'
terraform apply -var 'base=3.1' -var 'exp=-2'

#Gives NaN, weird, guess it doesn't like decimal exponent
terraform apply -var 'base=-3.1' -var 'exp=2.3'

#Checking maximums, 308 seems to be the max
terraform apply -var 'base=10' -var 'exp=309'
terraform apply -var 'base=10' -var 'exp=308'

Why use it?

This is a bit like the log function, both from a mathematical and usefulness perspective. Mathematically, this is the inverse operation of a log function. How useful this function is to deploying automated infrastructure is a bit more debatable. It is pretty easy to implement though, since the pow function is a part of the math package in Golang.

Lessons Learned

The function has an upper limit on value, so anything more than 10^308 is rendered as infinity. Since there are only about 10^82 atoms in the universe, I guess that’s more than sufficient. The function also does not like a negative base value with a decimal for the exponent. The resulting value is NaN. I checked and that is how Golang renders it as well, so that’s not an issue of implementation on Terraform’s part.

Coming up next is the replace() function.

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