Let's Learn: Terraform

What is Terraform?

• Terraform is an Infrastructure Automation tool.
• It is Open Source and Vendor Agnostic.
• It is a Single binary compiled from Go.
• It follows Declarative syntax.
• It uses HashiCorp Configuration Language(HCL) or JSON.
• Deployment is push based.

Core Components

• Executable
  • Can be downloaded from official Terraform webpage.
• Configuration files
• Provider plugins
• State data

Terraform Code Components

• It can be divided into 3 parts:
  • Inputs - Terraform gets input by leveraging variable(s).
  • Outputs - The data in the output block is printed to screen.
  • Logic - Your IaC.

Object Types

• Providers
• Resources
• Data sources

Terraform Syntax

• HashiCorp uses Block syntax

        block_type "label" "name_of_label" {
            key = "value"
  
            nested_block{
                key = "value"
            }
        }
  

  Workflow

• terraform init

  • Looks for configuration files in current working directory and examines them. If they need any provider plugins, it will search in public Terraform registry unless any specified location provided.

  • Terraform needs to store data of configuration somewhere as part of init process. A state data file will be created in current directory unless any specified backed it created or pointed.

  • When init completes, infrastructure is ready to be deployed.

• terraform plan

  • This step is optional.
  • It will look current configuration i.e. contents of state data and determine the difference. Then it draws a plan for Target environment to match the desired configuration.

• terraform apply

  • It will build our desired configuration in Target environment.

• terraform destroy

  • It will bring down the infrastructure of desired configuration in Target environment.

Terrafrom variable

• Variable declaration

        variable "name_of_variable" {}
  

• Variable definition

        variable "name_of_variable" {
            type = value
            description = "value"
            default = "value"
            sensitive = true or false
        }
  

  • Example

          variable "device_name" {
              type = string
              description = "Provides the Device name"
              default = "computer"
              sensitive = true
      }
    

• type - Data type

• Description - Context for the user. It will be displayed when the user encountered an error.
• default - This value will be considered if no value has been provided.

• sensitive - If it is 'true', data will not be printed in logs or terminal. If 'false', vice versa. Default sticks to 'false'.

• Referencing a variable

        var.<name_of_variable>
  

  • Example

          var.device_name
    

• Hierarchy

  • For variable(s) data or value, Terraform designed a precedence chart.

  • Precedence

    Environment variable(s) > .tfvars (or) .tfvars.json > .auto.tfvars (or) .auto.tfvars.json > -var-file flag > - var flag > CLI

Terraform Data Types

• Primitive

  • string
  • number
    • integer
    • decimal
  • boolean
    • true
    • false

• Collection

  • list

    • Enclosed with [ ]
    • Example

            [1,2,3]
            ["Mobile", "Computer", "Laptop"]
      

    • Variable reference
      • Example

         variable "list_of_device_types"{
             type = list(string)
             description = "Provides list of device types"
             default = ["Mobile","Computer","Laptop"]
         }
        

      • Syntax

              var.<name_of_variable>[<element_number>]
        

        • Example
          • var.list_of_device_types[0]
          • For accessing first element in list. Likewise for other elements accessing.

  • set

    • Same syntax as list and do not hold duplicates.

  • map

    • Enclosed with { }
    • Example

            {
                India = "Delhi"
                USA = "Washigton"
                Canada = "Ottawa"
            }
      

    • Variable reference

      • Example

              variable "capitals"{
                  type = map(string)
                  description = "Provides captials for countries."
                  default = {
                      India = "Delhi"
                      USA = "Washigton"
                      Canada = "Ottawa"
                  }
              }
        

      • Syntax

              var.<name_of_variable>.<name_of_the_key>
        
              or
        
              var.<name_of_the_variable>["name_of_the_key"]
        

      • Example
        • var.capitals.India or var.capitals["India"]
        • For accessing first element in map. Likewise for other elements accessing.
  • Note: Should hold same type of data.

• Structural

  • type
  • object

Terrafrom Locals

• Values provides in locals are computed inside the configuration and cannot be passed as parameter during runtime.

• Syntax

        locals{
            key : "value"
        }
  

• Example

        locals{
            name_of_the_company = "ThunderWonder"
        }
  

• Referencing locals
  • syntax

          local.<name_of_the_variable>
    

  • Example

          local.name_of_the_company
    

Terraform Output

• Output values are extracting information from Terraform.
• Output is printed to terminal screen at the end of configuration execution.

• It also exposes values when a configuration is placed inside a module.

• Syntax

        output "name_of_the_variable"{
            value = output_to_be_exposed
            description = string
            sensitive = true | false
        }
  

• Example

        output "selected_device"{
            value = var.list_of_device_types[0]
            description = "Prints selected device(s).
        }
  

Tip: If you want to validate your Terraform code. Type terraform validate.

• First run terraform init.
• terraform validate will check for your syntax and logic.
• It will not guarantee for successful deployment.

Terraform State Data

• It stored in JSON format
  • Important: It should not be modified. To work with State Data, we can use State commands.
• It contains Resource Mapping and metadata.

• It can be stored in:

  • Local (Default, by name terraform.tfstate)
  • Remote (Basically Cloud Providers)
    • Ex: AWS, Azure, Terraform Cloud, etc.

• State Commands

  • terraform state list
    • To list all state resources.
  • terraform state show <ADDRESS>
    • To show a specific resource.
    • Example :

        terraform state show module web_app_s3.aws_s3_bucket.web_bucket
      

  • terraform state mv SOURCE DESTINATION
    • To move an item in state file.
  • terraform state rm <ADDRESS>
    • To remove an item in state file.
    • Example:

            terraform state rm module web_app_s3.aws_s3_bucket.web_bucket
      

  • terraform state pull
    • Output current state to stdout.
  • terraform state push
    • Update remote state from local.

      Terraform Providers

• It contains Public & Private registries.
• Registries types are:
  • Official
    • Maintained by HashiCorp.
  • Verified
    • Maintained by Third Party and verified by HashiCorp.
  • Community
    • Maintained by Individuals in Community and not verified.
• Providers are Open Source and written in Go Lang.
• It has Resources and Data Sources.
• Providers are versioned.

Terraform Block Syntax

• It is used for configuring General Settings of Terraform Configuration like,
  • Version
  • Backend Settings for State Data
  • Required Provider Plugins
  • Provider metadata
  • Experimental features
• Syntax

        terraform{
            requried_providers {
                provider_name = {
                    source = "provider's_address"
                    version = "version_expression"
                }
            }
        }
  

  • Example

         terraform{
          requried_providers {
              aws = {
                  source = "hashicorp/aws"
                  version = "=3.0"
              }
          }
      }
    

Terraform Looping Constructs

• count

  • Takes integer and used as iterator.
  • index is used to keep track of count.
  • Example

          resource "aws_instance" "web_app_server"{
              count = 3
              tags = {
                  Name = "web-app-Instance-${count.index}
              }
          }
    

  • Referencing
    • Referring single instance

                <resource_type><name_of_the_variable>[element].<attribute>
      

    • Referring all the instances

                <resource_type><name_of_the_variable>[*].<attribute>
      

• for_each

  • used to for iterating Map or set/list.
  • Example

          resource "aws_s3_bucket_object" "website_content"{
              for_each = {
                  app_logo = "app-logo.png"
                  main_page = "index.html"
              }
              key      = each.value
              source   = "${each.value}"
          }
    

  • Referencing

          <resource_type><name_of_the_variable>[key].<attribute>
    

• Dynamic block
  • used to for iterating Map or set/list.

Terraform Inbuilt Functions

• Numeric Functions
• String Functions
• Collection Functions
• Encoding Functions
• Filesystem Functions
• Date and Time Functions
• Hash & Crypto Functions
• IP Network Functions
• Type Conversion Functions
• You can play around with in-built functions. Type terraform console and test it out.

• Example

  

• Check out Terraform Functions documentation for respective function methods, and it's usage.
• Note: Terraform does not support for User-defined functions.

Terraform FOR Expression

• Input type:
  • List, Set, Tuple, Map or, Object.
• Result type:
  • Tuple or Object

• Filtering is possible by leveraging if statement.

• Examples

  • Tuple

    • Syntax

            [for item in items : tuple_element]
      

    • Example

            locals{
                    devices = ["Mobile", "Laptop", "Tablet"]
            }
      
            [for device in local.devices : "Awesome-${device}"]
      

    • Result

      

  • Object

    • Syntax

            {for key, value in map : obj_key => obj_value}
      

    • Example

            locals{
                type_of_device{
                    Mobile = "compact"
                    Laptop = "productive"
                }
            }
      
            {for key, value in local.type_of_device : key => upper(value)}
      

    • Result

      

Terraform Workspaces

• Terraform creates a initial workspace for us called default.
• It cannot be deleted.
• We can create workspace(s) per our requirement and management.
  • Management like
    • State management
    • Variable values
    • Credential management, etc.

• workspace commands

  • terraform workspace list - To show all existing workspaces.
  • terraform workspace select <workspace_name> - To switch to desired workspace.
  • terraform workspace new <workspace_name> - To create & switch to new workspace.
  • terraform workspace delete <workspace_name> - To delete existing workspace.
  • terraform workspace show - To print current working workspace.

  • Example

    

Additional Resources

• Wanna try or start your Terraform practice ?
  • Start your Terraform practice today. For head start or reference check out my Terraform practice at GitHub. Feel free to fork and enhance your Terraform practice.
• Interested to learn more about variables like validations, limitations? Do check How to Use Terraform Variables.