DevOps Classroom Series – 08/Aug/2021

Terraform continued

• Loops:

  • Loops with the count parameter:

    • Basic psudeo code

    for(i=0; i<3 ; i++) {
        resource "" "" {
    
        }
    }
    

    • Refer Here for the changeset to create 3 subnets by using count property

  • Terraform has lot of inbuilt functions. Lets try to use the length function to make our count dynamic

  • Made use of length and create 3 more subnets by changing variable values in values.tfvars file Refer Here

  • Terraform has inbuilt functions for ip address. In this example we are using cidrsubnet function to calculate subnet range Refer Here for the changes

• Architecture realized so far

• So we need to add the following to the aws architecture

  • Add internet gateway and attach it to the vpc

  • For manual steps watch recording

  • Apply terraform changes to add internet gateway Refer Here

• Now lets create a public route table i.e. route to internet gateway and associate this with web subnets. Refer Here for the subnet associations to the public route table and routes

• Exercise: Create a private route table with associations to other subnets

• Lets create a ec2 instance in the public web subnet

  • To create ec2 instance we need a security group
  • Then create the ec2 instance as mentioned in the architecture

• Refer Here for the changes done

• Till now we were able to create a basic vm in aws vpc (network), so to be effective for enterprise needs we need to explore the following

  • Effective usage of variables
  • using terraform functions
  • To be able to delete and recreate particular resources rather than deleting the whole resources
  • How to create some reusable elements out of the work which we have done
  • Explore Azure also

• But before all of this lets deep dive on what happens when we apply resources in terraform.

Deep Dive into Terraform

• Terraform workflow as an Individual

  • Write – Author Infrastructure as code
  • Plan – Preview the changes before applying
  • Apply – Provision reproducable infrastructure

• Terraform with in a team

  • We follow the above steps
  • When we create infrastructure using apply and some other colleague also tries to apply there should be only environment created.

• Terraform apply always gives us the same result which is the desired state described in terraform configurations/template. This property is called as Idempotance

• Terraform apply command is actually combination of two commands

terraform plan
terraform apply

• Terraform plan command shows the changes required to meet the desired state
  • Plan will crosscheck your desired state with your destination environment (aws) and tells what has to done to accomplish/meet the desired state
  • Lets create a plan terraform plan -var-file="./values.tfvars" -out="ntier.plan".
  • Now to create infrastructure we can execute terraform apply "ntier.plan"
  • Now terraform creates the resources as per plan and creates some extra files
• So what are these state files.