Why Dynamic blocks in security groups in Terraform? - Purpose & Use Cases

The Big Idea

What if you could write one list and have all your security rules created perfectly every time?

The Scenario

Imagine you have to create a security group with many rules, each allowing different ports and IPs. You write each rule by hand, repeating similar code again and again.

The Problem

This manual way is slow and boring. If you want to add or change a rule, you must edit many places. It's easy to make mistakes or forget something. Managing many rules becomes a headache.

The Solution

Dynamic blocks let you write one simple loop that creates all the rules automatically. You just list the rules once, and Terraform builds the security group for you. It saves time and avoids errors.

Before vs After

✗ Before

ingress {
  from_port = 80
  to_port = 80
  protocol = "tcp"
  cidr_blocks = ["10.0.0.0/24"]
}
ingress {
  from_port = 443
  to_port = 443
  protocol = "tcp"
  cidr_blocks = ["10.0.1.0/24"]
}

✓ After

dynamic "ingress" {
  for_each = var.rules
  content {
    from_port = each.value.from_port
    to_port = each.value.to_port
    protocol = each.value.protocol
    cidr_blocks = each.value.cidr_blocks
  }
}

What It Enables

You can quickly create and update many security rules by changing just one list, making your infrastructure flexible and error-free.

Real Life Example

A company needs to open different ports for multiple teams. Instead of writing many blocks, they list the rules once. Terraform then builds the security group with all needed rules automatically.

Key Takeaways

Manual security group rules are repetitive and error-prone.

Dynamic blocks automate rule creation using simple lists.

This makes managing security groups faster and safer.