Plan output reading in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the 'terraform plan' command do?

It shows what changes Terraform will make to your infrastructure without applying them. Think of it like a preview before you make changes.

beginner

What information can you find in the output of 'terraform plan'?

You can see which resources will be added, changed, or destroyed. It tells you exactly what Terraform plans to do.

beginner

In Terraform plan output, what does a line starting with '+' mean?

It means a resource will be created (added). The '+' sign shows new resources.

beginner

What does a line starting with '-' indicate in Terraform plan output?

It means a resource will be destroyed (removed). The '-' sign shows resources that will be deleted.

beginner

Why is reading the Terraform plan output important before applying changes?

Because it helps you avoid mistakes by showing what will happen. You can catch unwanted deletions or changes before they happen.

What does the '+' symbol mean in Terraform plan output?

A No change to resource

B Resource will be destroyed

C Resource will be updated

D Resource will be created

The '+' sign means Terraform plans to add a new resource.

Which command shows the planned changes without applying them?

A terraform plan

B terraform init

C terraform destroy

D terraform apply

'terraform plan' previews changes without making them.

If you see a '-' sign next to a resource in the plan output, what does it mean?

A Resource will be unchanged

B Resource will be created

C Resource will be destroyed

D Resource will be renamed

The '-' sign means the resource will be deleted.

Why should you always read the plan output before applying?

A To check for syntax errors

B To preview changes and avoid mistakes

C To speed up deployment

D To update Terraform version

Reading the plan helps catch unwanted changes before applying.

What does Terraform show if a resource will be changed but not created or destroyed?

A ~

B -

C +

D !

The '~' symbol means the resource will be updated or changed.

Explain how to interpret the symbols '+' , '-' , and '~' in Terraform plan output.

Think of these symbols as signs showing what Terraform will do to each resource.

Describe why it is important to review the Terraform plan output before running 'terraform apply'.

It's like checking your work before pressing 'send' or 'submit'.

Practice

1. What does the terraform plan command primarily show before applying changes?

easy

A. The current cost of your cloud resources

B. The changes Terraform will make to your infrastructure

C. The list of all Terraform providers installed

D. The history of previous Terraform apply commands

Solution

1. Step 1: Understand the purpose of terraform plan

   This command previews the changes Terraform will perform on your infrastructure without applying them.

2. Step 2: Compare options with command purpose

   Only The changes Terraform will make to your infrastructure correctly describes this preview of changes. Other options describe unrelated information.

3. Final Answer:

   The changes Terraform will make to your infrastructure -> Option B

4. Quick Check:

   Plan shows changes = B [OK]

Hint: Plan shows what changes will happen before apply [OK]

Common Mistakes:

• Confusing plan with apply
• Thinking plan shows costs
• Assuming plan shows provider list

2. In Terraform plan output, what does the symbol ~ indicate?

easy

A. Resource will be updated

B. Resource will be created

C. Resource will be deleted

D. Resource will be ignored

Solution

1. Step 1: Recall Terraform plan symbols

   The symbol ~ means a resource will be updated (changed in place).

2. Step 2: Match symbol to meaning

   + means create, - means delete, so ~ must mean update.

3. Final Answer:

   Resource will be updated -> Option A

4. Quick Check:

   ~ means update = A [OK]

Hint: Remember + create, ~ update, - delete symbols [OK]

Common Mistakes:

• Mixing up ~ with + or -
• Thinking ~ means delete
• Assuming ~ means no change

3. Given this Terraform plan output snippet:

  # aws_instance.web will be updated in-place
  ~ resource "aws_instance" "web" {
      instance_type = "t2.micro" -> "t2.small"
    }

What does this output mean?

medium

A. The instance type will change from t2.micro to t2.small

B. No changes will be made to the instance

C. The instance will be deleted and recreated

D. The instance will be created new

Solution

1. Step 1: Analyze the plan output details

   The symbol ~ shows an in-place update. The instance_type changes from "t2.micro" to "t2.small".

2. Step 2: Interpret the meaning

   This means the existing instance will be updated to the new type without deletion.

3. Final Answer:

   The instance type will change from t2.micro to t2.small -> Option A

4. Quick Check:

   ~ means update, instance_type changed = C [OK]

Hint: Look for ~ and arrow showing old -> new value [OK]

Common Mistakes:

• Thinking resource will be deleted
• Ignoring the arrow showing value change
• Assuming no change because resource exists

4. You see this Terraform plan output:

  # aws_s3_bucket.example will be deleted
  - resource "aws_s3_bucket" "example" {
      bucket = "my-bucket"
    }

But you want to keep the bucket. What should you do?

medium

A. Ignore the plan and continue

B. Remove the resource from your Terraform config

C. Run terraform apply immediately

D. Add lifecycle rule with prevent_destroy to the resource

Solution

1. Step 1: Understand the delete plan

   The plan shows the bucket will be deleted, but you want to keep it.

2. Step 2: Use lifecycle prevent_destroy

   Adding a lifecycle block with prevent_destroy = true stops accidental deletion.

3. Final Answer:

   Add lifecycle rule with prevent_destroy to the resource -> Option D

4. Quick Check:

   Use prevent_destroy to block deletes = A [OK]

Hint: Use lifecycle prevent_destroy to stop unwanted deletes [OK]

Common Mistakes:

• Removing resource causes deletion
• Applying plan deletes bucket
• Ignoring plan risks data loss

5. You run terraform plan and see:

  # aws_security_group.sg will be replaced
  - resource "aws_security_group" "sg" {
      name = "old-sg"
    }
  + resource "aws_security_group" "sg" {
      name = "new-sg"
    }

What does this mean and why does Terraform replace the resource instead of updating it?

hard

A. Terraform will fail because name change is not allowed

B. Terraform updates the resource in place changing the name

C. Terraform deletes and recreates because the name attribute is immutable

D. Terraform ignores the change because names can be duplicated

Solution

1. Step 1: Analyze the plan output for replacement

   The plan shows the resource will be deleted (-) and a new one created (+) with a different name.

2. Step 2: Understand why replacement occurs

   Some attributes like security group name are immutable, so Terraform must replace the resource to change them.

3. Final Answer:

   Terraform deletes and recreates because the name attribute is immutable -> Option C

4. Quick Check:

   Immutable attribute change causes replacement = D [OK]

Hint: Immutable attribute changes cause resource replacement [OK]

Common Mistakes:

• Thinking Terraform updates name in place
• Assuming name can be duplicated
• Believing plan will fail on name change