Day-05

Terraform For Loops, Lists and Count Meta-Argument

Step-00: Pre-requisite Note

• We are using default vpc in ap-northeast-1 region

Step-01: Introduction

• Terrafrom Meta-Argument: count

• Terraform Lists & Map

  • List(string)

  • map(string)

• Terraform for loops

  • for loop with list

  • for loop with map

  • for loop with Map advanced

• Splat Operators

  • Legacy splat operator .*.

  • Generalized Splat Operator (latest)

  • Understand terraform generic splat expression [*] when dealing with count Meta-Argument and multiple output values.

Step-02: c1-versions.tf

No changes

step-03: c2-variables.tf - Lists and Maps

# AWS EC2 Instance type -List
variable "instance_type_list" {
  description = "ec2 instance type declaring in the list" 
  type = list(string)
  default = ["t3.micro", "t3.small"]
}

# AWS EC2 Instance type - Map
variable "instance_type_map" {
  description = "ec2 instance type declaring it in the Map"
  type = map(string)
  default = {
     "dev" = "t3.micro"
     "qa" = "t3.small"
     "prod" = "t3.large"
  }
}

Step-04: c3-ec2securitygroups.tf and c4-ami-datasource.tf

• No changes to both the files

Step-05: c5-ec2instance.tf

# How to reference List values ?
instance_type =var.instance_type_list[1]

# How to reference Map Values ?
instance_type = var.instance_type_map["prod"]

# Meta Argument count
count =2 

# count.index
tags = {
"name" = "count-demo-${count.index}"
}

Step-06: c6-outpts.tf

• for loop with list

• for loop with Map

• for loop with Map advanced

# Output - for loop with List
output "for_output_list" {
  description = "Gor loop with List"
  value = [for instance in aws_instance.myec2vm: instance.public_dns]
}

# Output - for loop with map
output "for_output_map" {
  description = "for loop with map"
  value = {for instance in aws_instance.myec2vm: instance.id=> instance.public_dns}
}

Step-07: Execute the terraform commands

terraform init -> terraform validate -> terraform plan -> terraform apply or terraform apply --auto-approve

Observations:

terraform plan -> play with Lists and Maps for instance_type

terraform apply -> two ec2 instances (count=2) of a resource myec2vm will be created
-> count.index will start from 0 and end with 1 for VM names
-> Review outputs in detail (for loop with list, maps)

Step-08: Clean-Up

#terraform destroy

terraform destroy --auto-approve

#Files
rm -rf .terraform*
rm -rf terraform.tfstate