Terraform · Infrastructure as code

When should you use count versus for_each?

Mediumcountfor eachinstancesUpdated Oct 2026

Short answer

count creates instances by index; for_each creates them by stable keys. Prefer for_each for collections so removing an item does not shift indexes and force unrelated replacements.

Both meta-arguments create multiple instances of one resource block. count gives each instance a numeric index, while for_each uses a map or set key. The address format differs: aws_instance.web[0] versus aws_instance.web["api"].

hcl

resource "aws_iam_user" "team" {
  for_each = toset(["asha", "ravi", "mei"])

  name = each.value
}

Removing Ravi removes only his instance. The other keys keep their identity.

hcl

resource "aws_instance" "web" {
  count         = var.enabled ? 2 : 0
  ami           = data.aws_ami.base.id
  instance_type = "t3.micro"
}

count is a natural fit for a simple on/off toggle or a fixed number of identical instances.

Trade-offs

count indexes shift when an item is removed from the middle
for_each keys are stable and survive reordering
count is concise for booleans and fixed replicas
for_each requires a map or set of known keys at plan time
Neither handles keys that are unknown until apply

Use count when the instances are interchangeable and the index has no meaning beyond position. Use for_each when each instance represents a named entity, such as a user, subnet or bucket. Do not build a for_each over a list; convert it to a map or set so keys are stable.

Changing a resource from count to for_each changes every address. Plan a state migration or use moved blocks for each instance, otherwise Terraform destroys and recreates them.

Follow-ups you should expect

Interviewers use these to check whether the first answer was understanding or memorisation.

1Why does removing an item from a count list cause churn?
2Can for_each iterate over a list?
3What happens when for_each keys are unknown at plan time?
4How do you migrate from count to for_each safely?

Say it in the interview

count gives instances numeric addresses, while for_each gives them stable keys. I prefer for_each for named collections, because deleting an item from the middle of a count list shifts every later index and can replace unrelated resources. count is still fine for a boolean toggle or a fixed number of identical replicas. Either way, changing the meta-argument changes addresses, so I plan a state migration.

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Trade-offs

Follow-ups you should expect

Related questions

Now say it out loud.