Dynamic blocks eliminate repetitive nested block duplication in Terraform resources

Some Terraform resources require multiple nested configuration blocks (e.g., security group ingress rules, ECS container definitions, policy statements). Writing each block by hand is verbose, repetitive, and difficult to maintain when the list of items comes from a variable.

Use dynamic blocks to generate repeated nested blocks from a collection. The content block inside dynamic defines the block body using each.value.

variable "ingress_rules" {
  type = list(object({
    port        = number
    protocol    = string
    cidr_blocks = list(string)
  }))
  default = [
    { port = 80,  protocol = "tcp", cidr_blocks = ["0.0.0.0/0"] },
    { port = 443, protocol = "tcp", cidr_blocks = ["0.0.0.0/0"] },
  ]
}

resource "aws_security_group" "web" {
  name   = "web-sg"
  vpc_id = var.vpc_id

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

Dynamic blocks allow the number and content of nested blocks to be driven by data, making modules flexible and eliminating repetition that would otherwise require copy-paste of nearly identical blocks.

Resources with a variable number of nested configuration blocks driven by user input