Terraform Basics: Variables, workflow, and loops structure.

Summary:
In this terraform basics I have covered some basic workflow commands, data structure, and use of for loops.
This is first blog of Terraform series. To begin your journey from zero to hero. 

Basic Workflow:

# This is the first command to run after writing a new config files. It is used to initilize working directory containing terraform config files. It downloades all the dependencies.
1. terraform init

# This is a command that syntactically validate and make sure your configuration files is consistent
2. terraform validate

# This command will create an execution plan about how your infrastructure will look like. So that you can look before applying.
3. terraform plan

# This command apply your infrastrucutre on your cloud provider.
4. terraform apply

# It will destory Terraform managed infrastructure.
5. terraform destroy

For Source Code Click here

Terraform Variables: List & Map

It is very important to understand some basic data structures before jumping into creating a 3-tier or multi-cloud infrastructure. And, for the terraform you only need to master the list and map with loops. However, it is important to learn different variable types that you can use within terraform.

List(string): A list can be used to store data of any type, such as strings, numbers, or objects, and can be of any length. Elements in a list are usually accessed by their position or index within the list, with the first element typically having an index of 0.
```
     ## Ec2-Instance type -list
     variable "instance_type_list" {
     description = "EC2 Instnace Type"
     type = list(string)
     default = ["t3.micro", "t3.small"]
     }
```

Map(string): A map is a data structure that allows you to associate values with keys. Maps are used to define a collection of related data, where each item is identified by a unique key. Maps can be used to store and manipulate data of different types, including strings, numbers, lists, and other maps.

 # AWS EC2 Instance Type - Map
     variable "instance_type_map" {
     description = "EC2 Instnace Type"
     type = map(string)
     default = {
         "dev" = "t3.micro"
         "qa"  = "t3.small"
         "prod" = "t3.large"
     }
     }

Use of Created List and map in our Terraform:

# to access list
resource "aws_instance" "my_instance" {
    ami= data.aws_ami.ubuntu.id
    instance_type = var.instance_type_list[0]
    count= 4  # meta argument, it will spin up 4 instances   
}
#to accesss map
resource "aws_instance" "my_instance_map" {
    ami=data.aws_ami.ubuntu.id
    instance_type = var.instance_type_map["prod"]
    count= 4

}

Use of Loop with List and Map:

# for loop with list
output "for_output_list" {
  description = "For Loop with List"
  value       = [for instance in aws_instance.my_instance : instance.private_ip]
}

#for loop with map
output "for_output_map" {
  description = "For Loop with Map"
  value       = { for instance in aws_instance.my_instance_map : instance.id => instance.public_dns }
}

However, it is better to use Splat Operator it will simply return the list, above examples is just a way of how we can use a loop.

output "splat_operator-output" {
  description = "Generalized Splat Expression"
  value       = aws_instance.my_instance[*].public_dns
}

For Running Terraform:

# from your terminal run
terraform init

terraform validate

terraform plan

terraform apply

terraform destroy

Nayan Shivhare's blog