Explaining `coalesce` Function in Terraform

The aim of this page📝 is to explain the concept of the `coalesce` function in Terraform based on the particular example of setting a default value for a variable.

• The coalesce function in Terraform takes any number of arguments and returns the first one that isn't null or an empty string.
• This function is useful for setting default values for variables.
• If the first argument to coalesce is set (i.e., it's not null or an empty string), that value will be used.
• If the first argument isn’t set, coalesce will check the second argument, and so on, until it finds a set value.
• If none of the arguments are set, coalesce will return null.
• The concept of COALESCE is indeed borrowed from SQL. It's a common function in many programming languages and environments, especially those that deal with databases. The function is used to handle null or missing values, which is a common issue in data management. By providing a way to specify default values, COALESCE helps ensure data integrity and consistency. This concept has been adapted to Terraform for similar purposes in managing infrastructure configurations.

CODE

Here is a particular example I have experienced:

locals {
  latency_threshold = coalesce(var.override_latency_threshold, 300)
}

In this code:

• A local value named latency_threshold is being defined.
• The coalesce function is being used to check the value of var.override_latency_threshold
• If var.override_latency_threshold is set, its value will be used for latency_threshold.
• If var.override_latency_threshold isn't set, 300 will be used as a default value.

LINKS

• Terraform Documentation
• Terraform Coalesce Function