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.