07-Terraform-Resources

Terraform Resource

Terraform Resource Block

• A Terraform Resource is a fundamental unit used to model and manage infrastructure components.

• Each resource block describes one or more infrastructure objects that you want to create, modify, or manage.

  • Example : s3 bucket, ec2 instance, RDS instance, Security Group, VPC

• resource Syntax

  resource "type" "name" {
      argument1 = "value1"
      argument2 = "value2"
      ......... = "......"
      ......... = "......"
      argumentn = "valuen"
  }

• Example of a Resource Block:

  resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  
  tags = {
  Name = "Linux"
  }
  
  }

  

  • resource: The keyword to start a resource block.
  • aws_instance:
    • The resource type, which defines what you're creating (e.g., an AWS EC2 instance).
    • Resource type determines the kind of infrastructure object it manages and what arguments and other attributes the resource supports
  • example:
    • The resource name, which is a unique identifier within your configuration.
    • Its a Local name ("example").
    • The name is used to refer to this resource from elsewhere in the same Terraform module, but has no significance outside that module's scope.
  • ami, instance_type and tags: Arguments or the Configuration parameters specific to the resource you're defining.

Terraform Resource Behaviors

Terraform resource behaviors refer to,

• How Terraform manages and interacts with resources in your infrastructure.
• These behaviors determine how resources are
  • created
  • destroyed
  • updated

1. Create :

   • Terraform attempts to create resources in your target infrastructure based on your configuration.
   • Terraform creates resources that exist in the configuration but are not associated(present) with a real infrastructure object in the state

2. Destroy :

   • Destroys resources that exist in the state/infra but no longer exist in the configuration.
   • Removing a resource from your Terraform configuration leads to the planned destruction of that resource in the infrastructure.

3. Update in-place :

   • update the resources whose arguments have changed
   • Terraform detects differences between the desired state in your configuration and the current state in the infrastructure. It plans and applies changes to update resources accordingly.

4. Destroy and re-create :

   • Terraform will destroy and re-create resources whose arguments have changed but which cannot be updated in-place due to remote API limitations
   • Example : Changing Availability zone of an AWS EC2 instance

5. Dependency Management :

   • Terraform ensures dependent resources are created or updated before resources that rely on them to avoid issues.

6. Concurrency Control :

   • Terraform manages resource operation concurrency to prevent conflicts and ensure consistency.

7. State Management :

   • Terraform maintains a state file that records the current state of the infrastructure, which is used to plan and apply updates.

Understanding Terraform Resource Behavior with Example

• Lets Create an AWS EC2 instance and understand Terraform Resource(EC2) Behavior

  1. Create Terraform provider block

     terraform {
     required_providers {
         aws = {
             source = "hashicorp/aws"
             version = "~-> 5.0"
         }
     }
     }
     
     provider "aws" {
         region = "us-east-1"
     
         default_tags {
             tags = {
             terraform = "yes"
             project = "terraform-learning"
             }
         }  
     }

  2. Create Resource (EC2) block

     resource "aws_instance" "example" {
     ami           = "ami-0df435f331839b2d6"
     instance_type = "t2.micro"
     
     tags = {
         Name = "Linux2023"
         Owner = "Venkatesh"
     }
     }

• Lets Execute Terraform commands to understand resource behavior

  1. terraform init : Initialize terraform

     • The terraform init command is used to initialize a Terraform configuration.
     • It sets up the necessary components and dependencies for Terraform to manage your infrastructure.
     • Downloading Providers and Modules: On executing terraform init command terraform downloads the plugin for provider (in our case AWS) under .terraform folder in the current directory
     • Locking and Tracking Dependencies: Terraform also creates a terraform.lock.hcl file to track provider and module versions.

  2. terraform validate : Validate terraform code

     • Validate the configuration files in a directory
     • Validate runs checks that verify whether a configuration is syntactically valid and internally consistent
     • Primarily useful for general verification of reusable modules, including correctness of attribute names and value types.
     • It is safe to run this command automatically
     • Validation requires an initialized working directory (terraform init) with any referenced plugins and modules installed
     • Example :
       • terraform validate with error statements to correct
       • In above case, resource should be aws_instance and not aws_ec2 hence terraform validate will show an error
       • terraform validate with no errors

  3. terraform fmt : format terraform code

     • The terraform fmt command is used to automatically format Terraform configuration files, promoting consistent coding style and improved readability.
     • Formatting: It standardizes the indentation, line breaks, and element ordering in your configuration files.
     • Syntax Rules: Enforces Terraform's syntax rules, ensuring proper indentation and formatting
     • Comments: Doesn't alter comments but ensures they are consistently styled.
     • It reformats files without changing the content or functionality of your configuration and is save to run the command anytime
     • when terraform fmt is executed, it lists the files that it formatted, if no files listed it means all files are well formatted.

  4. terraform plan : Review the terraform plan

     • The terraform plan command is used to create an execution plan for your Terraform configuration, showing the changes Terraform will make to your infrastructure.
     • Plan Infrastructure Changes: Compares the current state of your infrastructure to the desired state and plans the necessary changes.
     • Output Summary: Provides a human-readable summary of the planned changes, including creation, modification, and destruction of resources.
     • Detailed Information: Offers detailed information about planned changes, resource modifications, and dependencies.
     • Validation: Validates (terraform validate) your configuration for syntax errors and inconsistencies before applying changes.
     • Dry Run: terraform plan is a "dry run" command; it shows proposed changes without applying them.
     • Its safe to execute this command
     • terraform plan will require you to have your AWS Credentials set and you are able to connect/access your AWS infrastructure. You will receive below error, when AWS cred are not set
       Error: No valid credential sources found
     • setup AWS Credentials using your preferred methods
     • Example of terraform plan

  5. terraform apply : Create Resources by terraform

     • terraform apply is like pressing the "execute" button for your Terraform configuration.

     • It tells Terraform to create, update, or delete resources in your infrastructure based on your configuration.

     • Be very cautious before you provide approval for terraform apply command as it modifies your infrastructure

     • Lets understand terraform apply in more detail:

       1. Execution: Terraform analyzes your configuration and the current state of your infrastructure to identify the differences between the desired state and the actual state.

       2. Changes: Terraform takes action to make the actual state match the desired state, which can involve creating, updating, or deleting resources.

       3. User Confirmation: Before making any changes, Terraform shows you a summary of what it's about to do. It can be over-ridden with auto-approve

       4. User Approval: You must confirm by typing "yes" when prompted to ensure you're aware of the changes.

       5. Execution: Once you confirm, Terraform executes the changes, and you can see the progress in real-time.

       6. Completion: After applying the changes, Terraform provides a summary of what was created, updated, or deleted. It also updates the state file with the current state of your infrastructure.

     • Example of terraform apply

     • After you type yes to terraform apply prompt, terraform will start creating resources mentioned in the plan

     • You should also be able to check on your AWS Console resource (EC2) being created

     • Once terraform completes the execution you should be able to check on your AWS Console resource (EC2) successfully created.

  6. terraform destroy : destroy or delete Resources

     • terraform destroy is like the "off" switch for your Terraform-managed infrastructure.

     • It tells Terraform to tear down and delete all the resources in your infrastructure that were created or managed by Terraform.

     • Lets understand terraform destroy in more detail:

       1. Execution: Terraform analyzes your configuration and the current state of your infrastructure, just like terraform apply.
       2. Resource Destruction: However, instead of creating or updating resources, terraform destroy focuses on destroying and deleting them.
       3. User Confirmation: Similar to terraform apply, it shows you a summary of what it's about to destroy. It can be over-ridden with auto-approve.
       4. User Approval: You must confirm by typing "yes" when prompted, ensuring you're aware of the resources that are going to be deleted.
       5. Execution: Once you confirm, Terraform executes the destruction, and you can see the progress in real-time.
       6. Completion: After the resources are destroyed, Terraform provides a summary of what was deleted.

     • Example of terraform destroy

     • After you type yes to terraform destroy prompt, terraform will start destroying resources mentioned in the plan

     • You should also be able to check on your AWS Console resource (EC2) being shutting down and getting ready for termination

     • Once terraform completes the execution you should be able to check on your AWS Console resource (EC2) successfully terminated.

• terraform apply -auto-approve and terraform destroy -auto-approve

  • The -auto-approve flag is an option that can be added to the terraform apply command to skip the confirmation step.
  • When you use terraform apply -auto-approve or terraform destroy -auto-approve, Terraform will not ask for your confirmation and will immediately apply the changes described in the execution plan.
  • This can be useful for automation, scripting, or CI/CD pipelines where manual confirmation is not possible
  • However, be cautious when using -auto-approve in production environments, as it can lead to unintended changes if the execution plan is not thoroughly reviewed.
  • Always review the execution plan carefully before using -auto-approve to ensure that the changes are as expected and won't cause any issues in your infrastructure.

References :

• Resource Syntax
• Resource Behavior
• Provisioning Infrastructure with Terraform