Meta Arguments: count vs for_each with Output
📝 Abstract
In Terraform, managing multiple resources efficiently is a common requirement in real-world DevOps projects. While creating multiple instances may seem straightforward, choosing the right approach can significantly impact scalability, flexibility, and maintainability.
This blog explores Terraform meta arguments, specifically count and for_each, and demonstrates how they behave differently when creating multiple resources. It also covers how outputs change based on these approaches and when to use depends_on for explicit dependencies.
🎯 Objectives
After completing this blog, you will be able to:
Understand what meta arguments are in Terraform
Create multiple resources using count
Identify limitations of count
Use for_each for better flexibility
Handle outputs correctly for both approaches
Understand the use of depends_on
Meta arguments are special Terraform keywords that control resource behavior.
Common Meta Arguments:
count
for_each
depends_on
lifecycle
👉 In this tutorial, we focus on:
🔷 Step 2: Creating Multiple Resources using count
✅ Code
resource "aws_instance" "my_instance" {
count = 2
ami = var.ec2_ami_id
instance_type = var.ec2_instance_type
}
🔍 Explanation
aws_instance.my_instance[0]
aws_instance.my_instance[1]
🔷 Step 3: Output using count
output "ec2_public_ip" {
value = aws_instance.my_instance[*].public_ip
}
🧠 Concept
🔷 Step 4: Limitation of count
Using count has restrictions:
🔷 Step 6: Using for_each (Better Approach)
resource "aws_instance" "my_instance" {
for_each = {
Apurv-1 = "t2.micro"
Apurv-2 = "t2.medium"
}
ami = var.ec2_ami_id
instance_type = each.value
tags = {
Name = each.key
}
}
🧠 Explanation
👉 Each instance becomes unique and configurable
terraform apply
🔷 Step 7: Why Old Output Fails
💡
In the above outputs, we get a list of Public IPs and DNS values. However, the issue is that Terraform only returns a list of values, and it does not clearly indicate which IP belongs to which instance.
❌ Old Code
aws_instance.my_instance[*].public_ip
❗ Reason
count → returns list
for_each → returns map
👉 So [*] does not work here
🔷 Step 8: Correct Output with for_each
✅ Public IP
output "ec2_public_ip" {
value = [
for instance in aws_instance.my_instance :
instance.public_ip
]
}
✅ Public DNS
output "ec2_public_dns" {
value = [
for instance in aws_instance.my_instance :
instance.public_dns
]
}
✅ Private IP
output "ec2_private_ip" {
value = [
for instance in aws_instance.my_instance :
instance.private_ip
]
}
🔷 Step 9: Final Result
After applying for_each:
Different instance names ✅
Different instance types ✅
Correct outputs fetched ✅
🔷 Step 10: Understanding depends_on
✅ Definition
depends_on is used to explicitly define dependencies
⚙️ Example
depends_on = [
aws_security_group.my_groups,
aws_key_pair.my_key
]
🧠 When to Use
When Terraform cannot detect dependency automatically
When using hardcoded values
When dependencies are indirect
❌ When NOT to Use
key_name = aws_key_pair.my_key.key_name
👉 Terraform automatically handles this (implicit dependency)
🚀 Conclusion
Use count → for simple, identical resources
Use for_each → for flexible and scalable setups
Understand difference between list vs map outputs
Use depends_on only when required
👨💻 About the Author
“A complete Terraform series covering everything from fundamentals to advanced real-world infrastructure automation in a DevOps environment.”
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