Count vs for_each decision in Terraform - Visual Side-by-Side Comparison

Process Flow - Count vs for_each decision

Start: Define resource

↓

Choose between count or for_each

↓

count

↓

Create N instances

↓

Access by index

↓

End

This flow shows deciding between using count or for_each to create multiple resources in Terraform, then how instances are accessed.

Execution Sample

Terraform

resource "aws_instance" "example" {
  count = 3
  ami = "ami-123456"
  instance_type = "t2.micro"
}

resource "aws_instance" "example_map" {
  for_each = {a=1, b=2}
  ami = "ami-123456"
  instance_type = "t2.micro"
}

Creates 3 instances using count and 2 instances using for_each with keys 'a' and 'b'.

Process Table

Step	Resource	Count/for_each Value	Instances Created	Access Method	Notes
1	aws_instance.example	count=3	3 instances (index 0,1,2)	By index (example[0])	Creates 3 identical instances
2	aws_instance.example_map	for_each={a=1,b=2}	2 instances (keys 'a','b')	By key (example_map["a"])	Creates instances with keys
3	aws_instance.example	Access example[1]	Instance at index 1	Index access	Access second instance
4	aws_instance.example_map	Access example_map["b"]	Instance with key 'b'	Key access	Access instance with key 'b'
5	Decision	Use count if identical instances	N/A	N/A	Count is simpler for identical resources
6	Decision	Use for_each if unique keys needed	N/A	N/A	for_each allows mapping keys to instances
7	End	N/A	N/A	N/A	Resource creation complete

💡 All instances created and accessible by their respective methods; decision depends on use case.

Status Tracker

Variable	Start	After Step 1	After Step 2	Final
count	undefined	3	3	3
for_each	undefined	undefined	{"a":1,"b":2}	{"a":1,"b":2}
instances_count	0	3	3	3
instances_for_each	0	0	2	2

Key Moments - 3 Insights

Why can't I use count with a map or set to create uniquely keyed resources?

Count creates instances by number only, so it can't assign unique keys. See execution_table rows 1 and 2 where count creates indexed instances but for_each creates keyed instances.

How do I access a specific instance created with for_each?

You access it by its key, like example_map["a"]. This is shown in execution_table row 4, unlike count which uses numeric indexes.

When should I prefer count over for_each?

Use count when you want multiple identical resources without unique keys. This is explained in execution_table row 5.

Visual Quiz - 3 Questions

Look at the execution_table, how many instances does aws_instance.example create?

A 2

B 1

C 3

D 0

💡 Hint

Check execution_table row 1 under 'Instances Created'

At which step do we see accessing an instance by key?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look at execution_table row 4 under 'Access Method'

If you want to create 5 identical instances, which method is simpler according to the table?

A count = 5

B for_each with 5 keys

C for_each with a map of 3 keys

D count = 3

💡 Hint

Refer to execution_table row 5 about when to use count

Concept Snapshot

Terraform lets you create multiple resources using count or for_each.
Use count when you want N identical copies, accessed by index.
Use for_each when you want to create resources with unique keys, accessed by those keys.
Count uses a number; for_each uses a map or set.
Choose based on whether you need simple copies or keyed instances.

Full Transcript

This visual execution shows how Terraform decides between count and for_each to create multiple resources. Count creates a fixed number of identical instances accessed by numeric index. For_each creates instances based on keys from a map or set, accessed by those keys. The execution table traces creation and access steps, showing count creates 3 instances indexed 0 to 2, while for_each creates 2 instances with keys 'a' and 'b'. Variable tracking shows how count and for_each values change. Key moments clarify common confusions about access methods and when to use each. The quiz tests understanding of instance counts, access methods, and decision criteria. The snapshot summarizes the key differences and usage rules.