Dynamic blocks vs for_each decision in Terraform - Visual Side-by-Side Comparison

Process Flow - Dynamic blocks vs for_each decision

Start

↓

Identify repeated config

↓

Is block structure repeated?

No→Use for_each on resource

Yes↓

Use dynamic block inside resource

↓

Generate repeated nested blocks

↓

Apply configuration

Decide if repeated nested blocks need dynamic blocks or if repeated resources use for_each, then apply configuration accordingly.

Execution Sample

Terraform

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

  dynamic "ingress" {
    for_each = var.ingress_rules
    content {
      from_port = ingress.value.from
    }
  }
}

This code uses a dynamic block to create multiple ingress rules inside one security group resource.

Process Table

Step	Action	Input	Result	Notes
1	Start processing resource	aws_security_group example	Resource block begins	Prepare to configure security group
2	Evaluate for_each in dynamic block	var.ingress_rules = [{from=80}, {from=443}]	Two ingress blocks to generate	Dynamic block will loop twice
3	Generate first ingress block	ingress.value.from = 80	Ingress block with from_port=80 created	First nested block created
4	Generate second ingress block	ingress.value.from = 443	Ingress block with from_port=443 created	Second nested block created
5	Finish resource configuration	All blocks generated	Resource ready for deployment	Dynamic blocks replaced repeated nested blocks
6	Apply terraform plan	Resource with 2 ingress blocks	Security group created with 2 ingress rules	Deployment successful

💡 All dynamic blocks generated and resource configured, ready for deployment

Status Tracker

Variable	Start	After 1	After 2	Final
var.ingress_rules	[{from=80}, {from=443}]	[{from=80}, {from=443}]	[{from=80}, {from=443}]	[{from=80}, {from=443}]
ingress.value.from	N/A	80	443	N/A after loop

Key Moments - 2 Insights

Why use dynamic blocks instead of for_each on the resource?

Dynamic blocks are used when you need to repeat nested blocks inside a single resource, as shown in steps 2-4 of the execution_table. For_each on the resource creates multiple separate resources instead.

Can for_each replace dynamic blocks for nested repeated blocks?

No, for_each on the resource creates multiple resources, not multiple nested blocks inside one resource. Dynamic blocks handle repeated nested blocks inside a single resource (see step 3 and 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of ingress.value.from at Step 4?

A 80

B 443

C N/A

D 0

💡 Hint

Check the 'Input' column at Step 4 in execution_table

At which step does Terraform finish generating all dynamic blocks?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look for 'Finish resource configuration' in the 'Action' column

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

A There would be 3 rows generating ingress blocks instead of 2

B The resource would be duplicated 3 times

C The dynamic block would not run

D No change in execution_table

💡 Hint

Refer to how dynamic blocks loop over var.ingress_rules in steps 2-4

Concept Snapshot

Dynamic blocks repeat nested blocks inside one resource.
Use for_each to create multiple resources.
Dynamic blocks loop over a list to generate blocks.
For_each on resource duplicates whole resource.
Choose dynamic blocks for nested repeated config.
Choose for_each for multiple similar resources.

Full Transcript

This visual execution shows how Terraform decides between dynamic blocks and for_each. It starts by identifying repeated configuration. If nested blocks repeat inside one resource, dynamic blocks are used. If whole resources repeat, for_each is used on the resource. The example traces a security group resource with a dynamic ingress block looping over two rules. Each iteration creates one ingress nested block with a from_port value. After generating all blocks, the resource is ready for deployment. Variables track the list of ingress rules and current loop value. Key moments clarify that dynamic blocks create repeated nested blocks inside one resource, while for_each duplicates entire resources. The quiz tests understanding of loop values, step completion, and how changing input affects execution. The snapshot summarizes when to use dynamic blocks versus for_each in Terraform.