The Terraform lookup function is one that falls under the built-in functions category. It retrieves a single value of an element in a map. This function takes the map name, key, and a default value as its arguments and looks for the key in the specified map.
Full Answer
What is a LOOKUP() function in TerraForm?
In todays tutorial we will take a look at an interesting Terraform function called lookup (). The lookup () function can be used to lookup a particular value inside of a map, given its key and if the given key does not exist, the given default value is returned instead:
How to look up a value in a terraform list programmatically?
When using a Terraform list type to define an Array of value or objects, it may be necessary at times to lookup those values programmatically. The Terraform index () function can be used to lookup the index location of a value in a list.
What if the matching key is unavailable in TerraForm?
Even if the matching key is unavailable, Terraform can function by supplementing the default value without breaking the configuration as lookup acts as a search function with a default value. Functions such as lookup help users create more concise and clear Terraform configurations and are an excellent tool in any DevOps engineer’s IaC toolbox.
What is a map in TerraForm?
It helps to understand how Terraform defines the concept of a map before you learn about the lookup function. Maps in Terraform are a type of input variable that store multiple key-value pairs. While a single variable stores a single value, maps can store multiple values as key-value pairs.
What is the use of lookup in Terraform?
lookup retrieves the value of a single element from a map, given its key. If the given key does not exist, the given default value is returned instead.
What is map type in Terraform?
Maps are a collection of string keys and string values. These can be useful for selecting values based on predefined parameters such as the server configuration by the monthly price.
Can you write functions in Terraform?
The Terraform language does not support user-defined functions, and so only the functions built in to the language are available for use.
What is flatten in Terraform?
» flatten Function flatten takes a list and replaces any elements that are lists with a flattened sequence of the list contents.
What are two complex types in Terraform?
There are two categories of complex types: collection types (for grouping similar values), and structural types (for grouping potentially dissimilar values).
What is null Terraform?
null : a value that represents absence or omission. If you set an argument of a resource to null , Terraform behaves as though you had completely omitted it — it will use the argument's default value if it has one, or raise an error if the argument is mandatory.
How many types of loops are there in Terraform?
Below is a summary of the three main looping constructs found within the HashiCorp Configuration Language (HCL) used by Terraform. Basic loop meta-argument – uses a hardcoded number or used with length to loop over the number of variables in a list or map.
What language is Terraform written in?
GoTerraform / Programming languageTerraform is written in Hashicorp Configuration Language (HCL), which is a fully functional and immutable based programming language. Loops, if statements, variables, and much of the logic you would find in any programming language exists in Terraform.
What are Terraform modules?
A Terraform module is a set of Terraform configuration files in a single directory. Even a simple configuration consisting of a single directory with one or more .tf files is a module. When you run Terraform commands directly from such a directory, it is considered the root module.
What is dynamic Terraform?
Terraform dynamic blocks are a special Terraform block type that provide the functionality of a for expression by creating multiple nested blocks. The need to create identical (or similar) infrastructure resources is common.
What is local in Terraform?
Terraform Locals are named values which can be assigned and used in your code. It mainly serves the purpose of reducing duplication within the Terraform code. When you use Locals in the code, since you are reducing duplication of the same value, you also increase the readability of the code.
How do I convert a list to string in Terraform?
2 AnswersTransform the list to add the quotes: [for s in var. names : format("%q", s)]Join that result using , as the delimiter: join(", ", [for s in var. names : format("%q", s)])Add the leading and trailing markers: "[ ${join(",", [for s in var. names : format("%q", s)])} ]"
What is difference between map and object in Terraform?
Maps contain many things of one type. Objects contain a specific set of things of many types. This is a simplification.
What is map variable Terraform?
terraform-map-variable.tf A variable can have a map type assigned explicitly, or it can be implicitly declared as a map by specifying a default value that is a map. The above demonstrates both. Then, replace the aws_instance with the following: resource "aws_instance" "example" { ami = var.
What is a map variable?
A variable map is a definition of how to construct a property set in a given situation and of which changes to save. Each variable has one or more variable sources that define how to retrieve the variable value in a given mode (such as Quote, Order, or Any).
What is map of string in Terraform?
Maps are a collection of string keys and string values. These can be useful for selecting values based on predefined parameters such as the server configuration by the monthly price.
What is it?
Returns: Takes a map, a key, and an optional default value. Returns the value in the map that corresponds to the key if found. If not found, returns the optional default value or throws an error.
Why use it?
This has got to be one of the most used functions in Terraform. There are a ton of data sources that return a map of values you might want to parse through. AWS AMIs, Azure VMs, firewall rules, metadata tags. That’s just a few off the top of my head. If you’ve got a map of key pairs, lookup is your pal.
Lessons Learned
The documentation on the Terraform site states that the function will not work with nested maps, i.e. maps with maps as the value associated to a key. I tried using a nested map for funsies, and it didn’t throw an error. What I learned is that the function evaluates the presence of the key first.
