Iterator variable in Terraform - Step-by-Step Execution

Process Flow - Iterator variable

Start with collection

↓

Pick next item as iterator variable

↓

Use iterator variable in block

↓

More items?

Yes→Repeat pick next item

No↓

End iteration

Terraform loops over each item in a collection, assigning it to an iterator variable to use inside the loop block.

Execution Sample

Terraform

locals {
  names = ["app1", "app2", "app3"]
}

resource "null_resource" "example" {
  for_each = toset(local.names)
  triggers = {
    name = each.key
  }
}

This code loops over a list of names, using each name as an iterator variable to create resources.

Process Table

Step	Iterator Variable (each.key)	Action	Resource Created
1	"app1"	Assign first item to iterator variable	null_resource.example["app1"]
2	"app2"	Assign second item to iterator variable	null_resource.example["app2"]
3	"app3"	Assign third item to iterator variable	null_resource.example["app3"]
4	N/A	No more items, iteration ends	No new resource

💡 All items in the set processed, iteration stops.

Status Tracker

Variable	Start	After 1	After 2	After 3	Final
each.key	N/A	"app1"	"app2"	"app3"	N/A

Key Moments - 2 Insights

Why does the iterator variable change each step?

Because Terraform assigns each item from the collection to the iterator variable in order, as shown in execution_table steps 1 to 3.

What happens when all items are processed?

Iteration stops, no more resources are created, as shown in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the iterator variable value at step 2?

A "app2"

B "app1"

C "app3"

D N/A

💡 Hint

Check the 'Iterator Variable (each.key)' column at step 2 in the execution_table.

At which step does the iteration end?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

Look for the step where 'No more items, iteration ends' is noted in the Action column.

If the list had 4 names instead of 3, how would the execution table change?

A There would still be 4 steps, no change.

B There would be 5 steps, with the 4th step assigning the new name.

C There would be 3 steps only.

D The iteration would never end.

💡 Hint

Refer to the pattern in execution_table rows for each item processed.

Concept Snapshot

Terraform iterator variable:
- Loops over each item in a collection
- Assigns current item to iterator variable (e.g., each.key)
- Use iterator variable inside resource or block
- Iteration ends when all items processed
- Enables dynamic resource creation

Full Transcript

In Terraform, an iterator variable is used to loop over a collection like a list or set. Each item in the collection is assigned to the iterator variable one by one. This variable can then be used inside resource blocks to create multiple resources dynamically. The process continues until all items are processed, then the iteration stops. For example, looping over a list of names assigns each name to the iterator variable 'each.key' in turn, creating a resource for each name.