Terraform Modules

Question 1

What is a Terraform module?

Answer 1

A module is a “set” of terraform configuration file inside a folder.

Question 2

What’s a root module?

Answer 2

The set of configuration files inside the current working directory is known as “root” module.

Question 3

Is module a folder or a file?

Answer 3

A module is a directory which is nothing but the set of different configuration files.

Question 4

write the general syntax of using a module

Answer 4

module “name_of_module” {
source = “path of the directory”
[config…]
}

Question 5

how Terraform “senses” changes in source code of any module or addition/removal of any module?

Answer 5

Terraform doesn’t have any automated way to sense “changes” in the module. For this it relies on the user’s action.

Question 6

What’s the first step we should do, whenever we change a module or update same?

Answer 6

The first command, that we should run is “terraform init” before any other command like plan or apply.

Question 7

In which module should we provide the “backend” configuration?

Answer 7

It should always be provided into the root module.

Question 8

What will happen if we “hard-code” resources inside the modules?

Answer 8

In that case, whenever we use that module, we will get the same source name, which may lead to “name” conflicts. Hence we should “externalise” all inputs to the module.

Question 9

What’s the process of externalisation of variables from modules?

Answer 9

1. Create a new file called “variable.tf” in the module folder.
2. Consume the variable just like normal variable inside the main.tf of module.
3. Pass-on the variable information from “module” object like an “attribute”.

Question 10

Write the general syntax of passing the variable value to the “module” object.

Answer 10

module "my_module" {
   source = "../../my_module_path"
    var_1 = "value"
    var_2 = "value2"
}

Question 11

How can we restrict the “scope” of a variable within the modules? e.g. we want to create a variable to be used inside the module, but don’t want to expose them to the consumer of the module.

Answer 11

We can restrict the “scope” of the variable inside “module” only by using “local variables”.
The local variables are not allowed to be consumed outside the module.

Question 12

Write general syntax of local variables?

Answer 12

locals {
   first = "first"
    second = 34
   third = "third"
}

Question 13

How to consume a local variable within the module?

Answer 13

By using interpolation syntax with “local” prefix
“${local.first}”
“${local.second}”

Question 14

Is it possible to return anything from a module?

Answer 14

yes we can define our module in a way that it can return the value in the form of output variable.

Question 15

can we say terraform module are just like a function?

Answer 15

Yes, Terraform module behaves like a function as

1. They accepts the arguments in the form of variables
2. They process the information within “isolated” files inside the module folder
3. They return the information/data in the form of output variables.

Question 16

How to return any value from the module?

Answer 16

it can be done by using output variables. e.g. in output.tf file:
output “asg_name” {
value = “${aws_auto_scaling_group.asg.name}”
description = “Name of the ASG”
}

Question 17

How can we consume the output of the module?

Answer 17

The output of the module can be consumed by using "module" reference:
module.myModule.asg_name

Question 18

Can we provide the absolute path of the files?

Answer 18

No, in Terraform we are only allowed to provide the relative path, not “absolute” path.

Question 19

How Terraform interpret the relative path?

Answer 19

The Terraform always interpret the relative path as per the current working directory. Apart from this, it will start giving error.

Question 20

Terraform find relative path of the file, but if the file is in separate folder and we are working in another folder, how can we provide the path of the file?

Answer 20

The Terraform interpret path relative to the current working directory.
To solve path problem, Terraform provides different types of path references.

Question 21

What are different path references and how can we use them?

Answer 21

Different Path references are:

1. path.module: It is used when the file is inside the module and root module is different
2. path.root or path.cwd: It is used when we need to provide the file path in relative to the root module or cwd.

Question 22

Write the general syntax of consuming path reference types?

Answer 22

”${path.module/myFolder/myFile}”

Question 23

What are inline blocks? Is it preferrable?

Answer 23

Inline blocks are the blocks written inside the resource object e.g. ingress and egress
The use of inline block should be avoided, instead, we should be using all resource blocks, to give more flexibility to the user.

Question 24

How can we create versioning of the Terraform modules?

Answer 24

Since Terraform is just a source code and it doesn’t creates any artifacts, hence its versioning is controlled by “git tags”.

Question 25

Write the general syntax of creating different versions of Terraform modules?

Answer 25

git tag -a “v0.0.1” -m “new version”

git push –follow-tags

Question 26

How can we consume a new version of the module in our code?

Answer 26

It is consumed by references inside the “source”
module “my_module” {
source = “mypath?ref=v0.0.1”
}

Question 27

What’s the general syntax of importing the existing resource in Terraform module state file?

Answer 27

terraform import module… existing_resource_name

Question 28

What’s the general syntax of Terraform import?

Answer 28

terraform import

Question 29

My Terraform plan keeps telling me to update the IAM policy, what might be the issue?

Answer 29

The provider is changing the content of the policy, which is triggering the “diff”, hence the Terraform plan is asking to revert same to previous state.