Why dynamic blocks reduce repetition in Terraform - Visual Breakdown

Process Flow - Why dynamic blocks reduce repetition

Start with repeated blocks

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Identify repeated pattern

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Create dynamic block with for_each

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Terraform loops over items

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Generates multiple blocks dynamically

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Result: Less code, easier changes

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End

Dynamic blocks let Terraform repeat similar blocks automatically, so you write less code and avoid copying the same structure many times.

Execution Sample

Terraform

resource "aws_security_group" "example" {
  name = "example"

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

This Terraform code uses a dynamic block to create multiple ingress rules from a list, instead of writing each rule manually.

Process Table

Step	Action	Input	Output	Notes
1	Start resource definition	No ingress rules yet	Resource block with dynamic ingress block	Setup for dynamic block processing
2	Evaluate for_each	var.ingress_rules list with 2 rules	Loop over 2 ingress rules	Terraform prepares to create 2 ingress blocks
3	First iteration	ingress.value = first rule	Create ingress block with first rule's ports and CIDRs	First ingress block generated
4	Second iteration	ingress.value = second rule	Create ingress block with second rule's ports and CIDRs	Second ingress block generated
5	Finish dynamic block	All rules processed	Resource has 2 ingress blocks	Dynamic block replaced repetition
6	Apply resource	Resource with 2 ingress blocks	Security group created with 2 ingress rules	Deployment reflects dynamic blocks

💡 All ingress rules processed, dynamic block replaced repeated code blocks

Status Tracker

Variable	Start	After 1	After 2	Final
ingress.value	undefined	{from_port=80, to_port=80, protocol="tcp", cidr_blocks=["0.0.0.0/0"]}	{from_port=443, to_port=443, protocol="tcp", cidr_blocks=["0.0.0.0/0"]}	No more rules

Key Moments - 3 Insights

Why does Terraform loop over var.ingress_rules in the dynamic block?

Terraform uses the for_each expression to repeat the block for each item in var.ingress_rules, as shown in execution_table rows 2-4.

How does using a dynamic block reduce repetition compared to writing blocks manually?

Instead of writing each ingress block by hand, the dynamic block automatically creates them for each rule, reducing code duplication (see execution_table rows 3 and 4).

What happens if var.ingress_rules is empty?

The dynamic block creates zero ingress blocks, so no repeated blocks appear, avoiding empty or unused code sections.

Visual Quiz - 3 Questions

Look at the execution_table, what is ingress.value during the second iteration?

A {from_port=80, to_port=80, protocol="tcp", cidr_blocks=["0.0.0.0/0"]}

B {from_port=443, to_port=443, protocol="tcp", cidr_blocks=["0.0.0.0/0"]}

C undefined

D Empty list

💡 Hint

Check execution_table row 4 under Input column

At which step does Terraform finish creating all ingress blocks?

A Step 5

B Step 4

C Step 3

D Step 6

💡 Hint

Look for 'Finish dynamic block' in execution_table

If var.ingress_rules had 3 rules instead of 2, how would execution_table change?

A Terraform would error out

B The number of iterations stays 2

C There would be 3 iterations creating ingress blocks

D Only the first 2 rules are processed

💡 Hint

Refer to how for_each loops over all items in the list (execution_table rows 2-4)

Concept Snapshot

Terraform dynamic blocks let you write one block that repeats for each item in a list.
Use for_each inside dynamic to loop.
Terraform creates one block per item automatically.
This reduces manual repetition and makes code cleaner.
If the list is empty, no blocks are created.
Dynamic blocks improve maintainability and reduce errors.

Full Transcript

This visual execution shows how Terraform dynamic blocks reduce repetition by looping over a list of ingress rules. Initially, the resource has a dynamic block with for_each set to var.ingress_rules. Terraform evaluates the list and loops over each rule. For each iteration, it creates an ingress block with the rule's ports and CIDRs. After processing all rules, the resource ends up with multiple ingress blocks without manually writing each one. Variables like ingress.value change each iteration to the current rule. This approach avoids copying the same block multiple times and makes the code easier to maintain. If the list is empty, no ingress blocks are created, keeping the resource clean. The execution table traces each step from start to finish, showing how the dynamic block replaces repeated code with a loop.