terraform

Purpose

Terraform is a command-line tool for defining and provisioning infrastructure as code using declarative HCL (HashiCorp Configuration Language) files. It enables users to create, update, and destroy cloud resources in a repeatable, version-controlled manner.

When to Use

Use Terraform for managing multi-cloud environments, automating infrastructure deployments, or when you need version-controlled IaC for resources like VMs, networks, or databases. Apply it in scenarios involving AWS, Azure, or GCP provisioning, especially for dynamic scaling, disaster recovery setups, or CI/CD pipelines to ensure consistency.

Key Capabilities

• Declarative HCL syntax for defining resources, e.g., resource "aws_instance" "example" { ami = "ami-123456" instance_type = "t2.micro" } .

• Provider support for over 100 services; configure with blocks like provider "aws" { region = "us-west-2" } .

• State management via local files or remote backends (e.g., S3) to track resource changes.

• Module reuse for composing configurations; import with module "vpc" { source = "./modules/vpc" } .

• Variable interpolation and functions, such as count for loops or templatefile for dynamic configs.

Usage Patterns

To use Terraform, start by writing an HCL file (e.g., main.tf) defining resources and providers. Initialize the workspace with terraform init , review changes via terraform plan , and apply them with terraform apply . For automation, wrap commands in scripts and use environment variables for secrets. Always version control your .tf files in Git. For multi-environment setups, use workspaces: terraform workspace new dev then switch with terraform workspace select dev .

Common Commands/API

Run Terraform via CLI; key commands include:

• terraform init : Download providers and modules; use -upgrade to update dependencies.

• terraform plan -out=plan.tfplan -var="instance_type=t2.medium" : Generate an execution plan; specify variables via flags or files.

• terraform apply plan.tfplan : Apply the plan; add -auto-approve for non-interactive runs.

• terraform destroy -target=aws_instance.example : Destroy specific resources; use -force cautiously. For API integration, use Terraform's remote backend or the Terraform Cloud API (e.g., POST to https://app.terraform.io/api/v2/runs for runs), but require authentication via $TERRAFORM_TOKEN . Set provider credentials as env vars, e.g., export AWS_ACCESS_KEY_ID=$AWS_API_KEY and export AWS_SECRET_ACCESS_KEY=$AWS_SECRET_KEY .

Integration Notes

Integrate Terraform with CI/CD tools like GitHub Actions or Jenkins by adding steps in your workflow YAML, e.g.:

• name: Terraform Init run: terraform init
• name: Terraform Apply run: terraform apply -auto-approve

Use remote state backends for collaboration, e.g., configure in main.tf with terraform { backend "s3" { bucket = "my-terraform-state" key = "path/to/state" region = "us-west-2" } } . For secrets, inject via env vars (e.g., $AWS_ACCESS_KEY_ID ) or tools like Vault. Ensure provider versions are pinned in .tf files, like terraform { required_providers { aws = { source = "hashicorp/aws" version = "~> 4.0" } } } , to avoid breaking changes.

Error Handling

Handle errors by running terraform validate first to check HCL syntax; fix issues like missing brackets or invalid attributes. For provider errors, verify credentials (e.g., check $AWS_ACCESS_KEY_ID is set) and use terraform plan -detailed-exitcode to get specific codes (e.g., 2 for errors). Common patterns: wrap commands in try-catch blocks in scripts, e.g.:

try { terraform apply } catch { echo "Error: Apply failed; check logs for details" }

Debug with TF_LOG=DEBUG terraform apply to log provider interactions, and use terraform state pull to inspect state files for inconsistencies.

Usage Examples

• Create an AWS EC2 instance: Define in main.tf as resource "aws_instance" "web" { ami = "ami-0c55b159cbfafe1f0" instance_type = "t2.micro" tags = { Name = "web-server" } } . Then run terraform init , followed by terraform apply -auto-approve to provision it.

• Manage a simple VPC: In main.tf, add resource "aws_vpc" "main" { cidr_block = "10.0.0.0/16" } and resource "aws_subnet" "subnet1" { vpc_id = aws_vpc.main.id cidr_block = "10.0.1.0/24" } . Execute terraform plan to review, then terraform apply for deployment.

Graph Relationships

• Connected to cluster: devops-sre

• Related tags: terraform, iac, devops

• Links to other skills: via devops-sre (e.g., ansible for configuration management), and iac-related tools like pulumi or cloudformation for alternative provisioning methods.