For_each for map-based instances in Terraform - Step-by-Step Execution

Process Flow - For_each for map-based instances

Define map variable

↓

Start for_each loop

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Iterate over each map key-value pair

↓

Create resource instance using key and value

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Repeat for all map entries

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End loop with all instances created

Terraform reads a map variable, then loops over each key-value pair to create a resource instance for each entry.

Execution Sample

Terraform

variable "servers" {
  type = map(string)
  default = {
    web = "10.0.0.1"
    db  = "10.0.0.2"
  }
}

resource "aws_instance" "example" {
  for_each = var.servers
  ami      = "ami-123456"
  instance_type = "t2.micro"
  private_ip = each.value
}

Creates one AWS instance per map entry, using the map key as instance name and value as private IP.

Process Table

Step	Map Key	Map Value	Resource Instance Created	Instance Private IP
1	web	10.0.0.1	aws_instance.example["web"]	10.0.0.1
2	db	10.0.0.2	aws_instance.example["db"]	10.0.0.2
3	-	-	-	All map entries processed, loop ends

💡 All map entries processed, no more keys to iterate

Status Tracker

Variable	Start	After 1	After 2	Final
each.key	-	web	db	-
each.value	-	10.0.0.1	10.0.0.2	-
resource count	0	1	2	2

Key Moments - 2 Insights

Why does Terraform use the map key as the instance identifier in the resource?

Terraform uses the map key as the unique identifier to create separate resource instances, as shown in execution_table rows 1 and 2 where aws_instance.example["web"] and aws_instance.example["db"] are created.

What happens if the map is empty?

If the map is empty, the for_each loop does not run any iterations, so no resource instances are created. This is implied by the exit_note in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the private IP of the instance created at step 2?

A 10.0.0.1

B 10.0.0.2

C ami-123456

D t2.micro

💡 Hint

Check the 'Instance Private IP' column at step 2 in the execution_table.

At which step does Terraform finish creating all instances from the map?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the exit_note and the last row in the execution_table.

If the map had three entries instead of two, how would the resource count change in variable_tracker after the last iteration?

A It would be 2

B It would be 1

C It would be 3

D It would be 0

💡 Hint

Refer to the 'resource count' row in variable_tracker and how it increments per iteration.

Concept Snapshot

Terraform for_each with map:
- Use for_each = var.map to loop over map entries
- each.key is map key, each.value is map value
- Creates one resource per map entry
- Resource instances named by map keys
- Useful for dynamic multiple resource creation

Full Transcript

This visual execution shows how Terraform uses for_each with a map variable to create multiple resource instances. It starts by defining a map with keys and values. Then, Terraform loops over each key-value pair. For each pair, it creates a resource instance named by the key and uses the value for configuration, such as private IP. The execution table tracks each step, showing the key, value, resource created, and IP assigned. The variable tracker shows how each.key, each.value, and resource count change with each iteration. Key moments clarify why keys are used as identifiers and what happens if the map is empty. The quiz tests understanding of instance IPs, loop completion, and resource count changes. This method helps create multiple similar resources efficiently using map data.