Terraform's declarative approach - Step-by-Step Execution

Process Flow - Terraform's declarative approach

Write desired state in config

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Run terraform plan

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Terraform compares current state

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Shows changes needed

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Run terraform apply

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Terraform makes changes to match desired state

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Infrastructure matches config

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End

Terraform lets you write what you want your cloud setup to look like. It then figures out what to change to make it so.

Execution Sample

Terraform

resource "aws_s3_bucket" "mybucket" {
  bucket = "my-unique-bucket-123"
  acl    = "private"
}

This code declares a private S3 bucket named 'my-unique-bucket-123'. Terraform will create or update the bucket to match this.

Process Table

Step	Action	Terraform State	Planned Change	Result
1	Read config file	No bucket exists	Create bucket 'my-unique-bucket-123'	Plan shows bucket creation
2	Run terraform apply	No bucket exists	Create bucket 'my-unique-bucket-123'	Bucket created in cloud
3	Run terraform plan again	Bucket exists as declared	No changes needed	Plan shows no changes
4	Change acl to 'public-read' in config	Bucket acl is 'private'	Update bucket acl to 'public-read'	Plan shows acl update
5	Run terraform apply	Bucket acl is 'private'	Update bucket acl to 'public-read'	Bucket acl updated
6	Run terraform plan	Bucket acl is 'public-read'	No changes needed	Plan shows no changes

💡 Terraform stops planning when the actual infrastructure matches the declared desired state.

Status Tracker

Variable	Start	After Step 2	After Step 5	Final
Bucket existence	False	True	True	True
Bucket acl	N/A	private	public-read	public-read

Key Moments - 3 Insights

Why does Terraform show changes even if I only wrote the desired state once?

Terraform compares the current real infrastructure with your desired state (see execution_table step 1). It plans changes to make them match.

What happens if I run 'terraform apply' without changing the config?

Terraform sees no difference between current and desired state (step 3), so it does nothing.

How does Terraform know what to change when I update the config?

It compares the old state with the new desired state and plans only the differences (step 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the planned change at step 4?

A Update bucket acl to 'public-read'

B Create a new bucket

C Delete the bucket

D No changes needed

💡 Hint

Check the 'Planned Change' column at step 4 in the execution_table.

At which step does Terraform first create the bucket?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Result' column to see when the bucket is created.

If you run 'terraform plan' after step 6, what will it show?

A Plan to delete the bucket

B No changes needed

C Plan to create a new bucket

D Plan to update bucket acl to 'private'

💡 Hint

See the 'Planned Change' at step 6 in the execution_table.

Concept Snapshot

Terraform's declarative approach means you write what you want, not how to do it.
Terraform compares your desired state with the real state.
It plans only the changes needed to match.
Apply makes those changes.
Repeated plans show no changes if states match.

Full Transcript

Terraform uses a declarative approach where you write configuration files describing the desired cloud infrastructure. When you run 'terraform plan', it compares this desired state with the current real infrastructure state. It then shows what changes it will make to match your configuration. Running 'terraform apply' executes those changes. If you run 'terraform plan' again without changes, it shows no changes needed. If you update your config, Terraform plans only the differences and applies them. This way, you manage infrastructure by declaring the end state, and Terraform handles the steps to get there.