DevOps Classroom notes 19/Sep/2024

Terraform contd

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Activity 2: Create a virtual network in Azure (contd)

• we have already created a resource group
• For Manual steps watch classroom video
• Refer Here for the changes done

Dependencies

• When a resource in a terraform uses attributes of other resource then an implicit dependency is created i.e the current resource will not be created until the other resource is created
• Dependencies can be made explicit by adding a meta argument depends_on Refer Here

idempotance

• Terraform execution is idempotent as execution irrespective of number of times will give you the same result (i.e desired state)

Terraform console

• Refer Here

Reasons for writing Template

• We would want to reuse the terraform templates across various environments and for every environment there will be changes
• Changes can be in
  • names
  • values
  • count of items
• Try to make terraform template generic not specific
• Specific example

def multiply():
    return 10 * 20

• Generic

# required arguments
def multiply(a, b):
    return a * b

# default arguments
def multiply(a=10, b=20):
    return a * b

Activity 1.1: Lets change the vpc template

• Lets ask the user the vpc cidr range and subnet cidr ranges
• Lets ask the user for the Name of vpc and subnets
• Exercise: Try implementing variables

Activity 2.1: Lets change the virtual network template

• Lets ask the user the vnet cidr range and subnet cidr ranges
• Lets ask the user for the Name of virtual network and subnets
  Refer Here for changes

Variable

• Refer Here for official docs
• Terraform provides variables where user can set values while applying
• Variable definition

variable "<variable_name>" {
    type =  string | number | bool | map | object | list
    description = 
    default = 
}

• Lets look at example

# definition
variable "vpc_cidr" {
    type = string
    default = "10.0.0.0/16"
    description = "vpc cidr"
}

resource "aws_vpc" "base" {
    # usage
    cidr_block = var.vpc_cidr
}

• Good practice is to define all variables in a file called as variables.tf or inputs.tf
• Variables can be passed at runtime during apply by adding -var to the apply

terraform apply -var vpc_cidr='192.168.0.0/16'