Ignore_changes lifecycle rule in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the ignore_changes lifecycle rule do in Terraform?

It tells Terraform to ignore changes to specified resource attributes during updates, so those changes won't trigger resource replacement or updates.

beginner

How do you specify attributes to ignore changes for in Terraform?

Inside the resource block, use lifecycle { ignore_changes = ["attribute_name"] } to list attributes Terraform should ignore when they change.

intermediate

Why would you use ignore_changes in a Terraform configuration?

To prevent Terraform from overwriting manual changes made outside Terraform or to avoid unnecessary resource updates for attributes that change frequently but don't need management.

advanced

Can ignore_changes be used with nested attributes or lists?

Yes, you can specify nested attributes using dot notation like ignore_changes = ["settings.0.name"] to ignore changes in nested blocks or list elements.

advanced

What happens if you ignore changes to a required attribute in Terraform?

Terraform will not update the resource when that attribute changes outside Terraform, which might cause drift between actual and desired state, so use ignore_changes carefully.

What is the purpose of the ignore_changes lifecycle rule in Terraform?

A To delete resources automatically

B To force Terraform to always update specified attributes

C To prevent Terraform from updating specified attributes when they change outside Terraform

D To create new resources only

The ignore_changes rule tells Terraform to ignore changes to specified attributes, avoiding updates triggered by external changes.

How do you write the ignore_changes rule inside a Terraform resource?

A lifecycle { ignore_changes = ["attribute"] }

B ignore_changes = true

C resource { ignore_changes = ["attribute"] }

D ignore_changes { attribute = true }

The correct syntax is inside the lifecycle block: lifecycle { ignore_changes = ["attribute"] }.

Which of these is a valid reason to use ignore_changes?

A To ignore manual changes made outside Terraform

B To force Terraform to overwrite all changes

C To delete resources automatically

D To create resources faster

Ignoring manual changes prevents Terraform from overwriting changes made outside its control.

Can ignore_changes be used to ignore changes in nested attributes?

A Only for string attributes

B No, it only works on top-level attributes

C Only for list attributes, not nested blocks

D Yes, using dot notation like "block.0.attribute"

Terraform supports ignoring nested attributes using dot notation in ignore_changes.

What risk comes with ignoring changes to required attributes?

A Terraform will delete the resource

B Resource drift and inconsistent state

C Terraform will fail to plan

D No risk, it is always safe

Ignoring required attributes can cause Terraform's state to drift from the real resource state.

Explain how the ignore_changes lifecycle rule works in Terraform and when you might use it.

Think about how Terraform manages resource updates and what happens if changes happen outside Terraform.

Describe how to ignore changes to a nested attribute in a Terraform resource using ignore_changes.

Consider how Terraform represents nested blocks and lists in configuration.

Practice

1. What is the main purpose of the ignore_changes lifecycle rule in Terraform?

easy

A. To prevent Terraform from updating specified resource attributes during apply

B. To delete resources automatically when attributes change

C. To force Terraform to recreate resources on every apply

D. To enable Terraform to ignore syntax errors in configuration files

Solution

1. Step 1: Understand the role of ignore_changes

   This rule tells Terraform to skip updating certain attributes even if they change outside Terraform.

2. Step 2: Compare options with this behavior

   Only 'To prevent Terraform from updating specified resource attributes during apply' matches this behavior by preventing updates on specified attributes.

3. Final Answer:

   To prevent Terraform from updating specified resource attributes during apply -> Option A

4. Quick Check:

   ignore_changes skips updates = D [OK]

Hint: Remember: ignore_changes skips updates on chosen attributes [OK]

Common Mistakes:

• Thinking ignore_changes deletes resources
• Confusing ignore_changes with forcing recreation
• Believing ignore_changes fixes syntax errors

2. Which of the following is the correct syntax to ignore changes on the attribute tags in a resource lifecycle block?

easy

A. lifecycle { ignore_changes = tags }

B. lifecycle { ignore_changes = ["tags"] }

C. lifecycle { ignore_changes = { tags = true } }

D. lifecycle { ignore_changes = "tags" }

Solution

1. Step 1: Recall the correct syntax for ignore_changes

   It requires a list of attribute names as strings inside square brackets.

2. Step 2: Match options to this syntax

   Only lifecycle { ignore_changes = ["tags"] } uses a list with quotes around "tags" correctly.

3. Final Answer:

   lifecycle { ignore_changes = ["tags"] } -> Option B

4. Quick Check:

   ignore_changes needs list of strings = A [OK]

Hint: Use square brackets and quotes for ignore_changes list [OK]

Common Mistakes:

• Omitting square brackets for the list
• Using a map or boolean instead of list
• Passing a single string without brackets

3. Given this Terraform resource snippet:

resource "aws_instance" "example" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
  tags = {
    Name = "example-instance"
  }

  lifecycle {
    ignore_changes = ["tags"]
  }
}

If someone manually changes the tags in AWS console, what will happen when you run terraform apply next time?

medium

A. Terraform will throw an error about tag drift

B. Terraform will overwrite the tags back to the config values

C. Terraform will keep the manual tag changes and not overwrite them

D. Terraform will recreate the instance to fix tags

Solution

1. Step 1: Understand ignore_changes effect on tags

   ignore_changes on "tags" means Terraform ignores any changes to tags outside Terraform.

2. Step 2: Predict apply behavior

   Terraform will not overwrite manual tag changes and will keep them as is.

3. Final Answer:

   Terraform will keep the manual tag changes and not overwrite them -> Option C

4. Quick Check:

   ignore_changes on tags keeps manual changes = C [OK]

Hint: ignore_changes means Terraform skips updating those attributes [OK]

Common Mistakes:

• Assuming Terraform always overwrites manual changes
• Expecting errors on drift with ignore_changes
• Thinking resource will be recreated due to tag changes

4. You wrote this lifecycle block:

lifecycle {
  ignore_changes = "tags"
}

Terraform plan shows an error. What is the problem and how to fix it?

medium

A. ignore_changes cannot include tags attribute

B. ignore_changes requires a boolean value, not string

C. ignore_changes must be outside lifecycle block

D. ignore_changes must be a list, fix by using ["tags"]

Solution

1. Step 1: Identify syntax error in ignore_changes value

   ignore_changes expects a list of attribute names, not a single string.

2. Step 2: Correct the syntax

   Wrap "tags" in square brackets to make it a list: ["tags"]

3. Final Answer:

   ignore_changes must be a list, fix by using ["tags"] -> Option D

4. Quick Check:

   ignore_changes needs list syntax = B [OK]

Hint: ignore_changes always needs a list, even for one attribute [OK]

Common Mistakes:

• Passing a single string instead of list
• Placing ignore_changes outside lifecycle block
• Using boolean instead of list for ignore_changes

5. You manage an AWS S3 bucket with Terraform. The bucket has a versioning block that is sometimes changed manually outside Terraform. You want Terraform to manage all bucket settings except ignore changes to versioning.enabled. How do you configure ignore_changes correctly?

hard

A. lifecycle { ignore_changes = ["versioning[0].enabled"] }

B. lifecycle { ignore_changes = ["versioning.enabled"] }

C. lifecycle { ignore_changes = ["versioning"] }

D. lifecycle { ignore_changes = ["versioning.enabled.enabled"] }

Solution

1. Step 1: Understand nested attribute syntax in ignore_changes

   For nested blocks like versioning, Terraform uses index notation like versioning[0].enabled to specify the attribute.

2. Step 2: Choose the correct attribute path

   lifecycle { ignore_changes = ["versioning[0].enabled"] } uses the correct syntax with index 0 for the first versioning block and the enabled attribute.

3. Final Answer:

   lifecycle { ignore_changes = ["versioning[0].enabled"] } -> Option A

4. Quick Check:

   Nested block attribute needs index notation = A [OK]

Hint: Use index like versioning[0].enabled for nested block attributes [OK]

Common Mistakes:

• Ignoring index notation for nested blocks
• Using incomplete attribute path
• Ignoring nested block structure in ignore_changes