Ignore_changes lifecycle rule in Terraform - Step-by-Step Execution

Process Flow - Ignore_changes lifecycle rule

Start Terraform Apply

↓

Check resource config changes

↓

Is attribute in ignore_changes?

Yes→Skip updating that attribute

No↓

Apply changes to resource

↓

Finish Apply

Terraform checks resource changes, skips updates to attributes listed in ignore_changes, then applies other changes.

Execution Sample

Terraform

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

  lifecycle {
    ignore_changes = ["tags"]
  }
}

This resource ignores changes to the 'tags' attribute during terraform apply.

Process Table

Step	Resource Attribute	Change Detected	In ignore_changes?	Action Taken
1	ami	Changed from ami-111111 to ami-123456	No	Update applied
2	instance_type	No change	No	No action
3	tags	Changed from {Name=old} to {Name=new}	Yes	Change ignored
4	Apply complete	-	-	Resource updated except tags

💡 All changes processed; tags change ignored due to lifecycle ignore_changes rule.

Status Tracker

Attribute	Initial Value	Detected Change	Final Applied Value
ami	ami-111111	ami-123456	ami-123456
instance_type	t2.micro	t2.micro	t2.micro
tags	{Name=old}	{Name=new}	{Name=old}

Key Moments - 2 Insights

Why does Terraform not update the 'tags' attribute even though it changed?

Because 'tags' is listed in ignore_changes, Terraform skips updating it as shown in execution_table step 3.

Does ignore_changes prevent Terraform from detecting changes?

No, Terraform detects changes but skips applying them for attributes in ignore_changes, as seen in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 1 for the 'ami' attribute?

A No change detected

B Change ignored

C Update applied

D Error occurs

💡 Hint

Check the 'Action Taken' column at step 1 in execution_table.

At which step does Terraform skip applying a change due to ignore_changes?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for 'Change ignored' in the 'Action Taken' column in execution_table.

If 'tags' were removed from ignore_changes, what would happen at step 3?

A Terraform would apply the tags change

B Change ignored as before

C Terraform would error out

D No change detected

💡 Hint

Refer to variable_tracker and execution_table to see how ignore_changes affects applying changes.

Concept Snapshot

Terraform lifecycle ignore_changes rule:
- Syntax: lifecycle { ignore_changes = ["attribute"] }
- Terraform detects changes but skips applying listed attributes
- Useful to avoid overwriting manual or external changes
- Applies only during terraform apply
- Other attributes update normally

Full Transcript

Terraform's ignore_changes lifecycle rule tells Terraform to detect but not apply changes to specified resource attributes. When Terraform runs apply, it compares current and desired states. If an attribute is in ignore_changes, Terraform skips updating it even if it changed. This helps keep manual or external changes intact. Other attributes update normally. For example, if tags are ignored, Terraform will not overwrite tag changes but will update other attributes like ami or instance_type.

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