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 #

1. 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.

2. 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.

3. terraform apply

   • It will build our desired configuration in Target environment.

4. 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

  ![Functions.png](/img/blog/lets-learn-terraform/T7w18-XMe.png align="left")

• 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

      ![For_Tuple.png](/img/blog/lets-learn-terraform/ipDb8qVF4.png align="left")

  • 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

      ![For_Object.png](/img/blog/lets-learn-terraform/zwIYlHmBn.png align="left")

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

    ![Workspaces.png](/img/blog/lets-learn-terraform/u2oR4JsBM.png align="left")

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.