Terraform State

Terraform State

Terraform State is how Terraform keeps track of the infrastructure it manages.

By default, Terraform stores state in:

terraform.tfstate

1. Why Does Terraform Need State?

Suppose we write:

resource "aws_instance" "backend" {
  ami           = "ami-123456"
  instance_type = "t3.micro"
}

Then run:

terraform apply

AWS creates:

EC2 Instance
ID: i-0123456789

Terraform needs to remember:

aws_instance.backend
        │
        │ maps to
        ▼
i-0123456789

That mapping is stored in the state file.

Terraform Code
      │
      ▼
Terraform State
      │
      ▼
Actual AWS Resource

aws_instance.backend
      │
      ▼
i-0123456789

2. How Terraform Uses State

Suppose the current configuration is:

instance_type = "t3.micro"

And the state knows the existing EC2 instance.

Now we change:

instance_type = "t3.small"

When we run:

terraform plan

Terraform compares:

Desired Configuration
        │
        │
        ▼
   Terraform State
        │
        │
        ▼
Actual Infrastructure

Then Terraform determines:

Current:
t3.micro

Desired:
t3.small

      ↓

Update required

This is how Terraform knows what needs to be created, updated, or deleted.

3. Important State Commands

View the current state:

terraform show

List resources tracked by Terraform:

terraform state list

Example:

aws_vpc.main
aws_subnet.public
aws_instance.backend
aws_s3_bucket.uploads

Inspect one resource:

terraform state show aws_instance.backend

4. Don’t Manually Edit terraform.tfstate

Avoid opening the state file and manually changing values.

Use Terraform commands instead.

❌ Manually modify terraform.tfstate

✅ Use Terraform commands

The state contains important mappings between Terraform resources and real infrastructure.

5. State Locking

Two developers should not modify the same state simultaneously.

Without locking:

Developer A ──┐
              ├──→ Same State
Developer B ──┘

       ⚠ Conflict

State locking prevents concurrent Terraform operations from corrupting or conflicting with state.

Conceptually:

Developer A
     │
     ▼
Acquire Lock
     │
     ▼
terraform apply
     │
     ▼
Update State
     │
     ▼
Release Lock

Modern Terraform S3 backends can support S3-based locking with:

use_lockfile = true

Example:

terraform {
  backend "s3" {
    bucket       = "taskify-terraform-state"
    key          = "production/terraform.tfstate"
    region       = "ap-south-1"
    use_lockfile = true
  }
}