Convert Terraform Dynamic Blocks to JSON

Terraform Dynamic Blocks

Dynamic blocks allow you to generate repeated nested blocks based on a collection. They replace manual repetition of similar blocks with a programmatic approach.

HCL Dynamic Block Example

resource "aws_security_group" "web" {
  name        = "web-sg"
  description = "Security group for web servers"
  vpc_id      = "aws_vpc.main.id"

  dynamic "ingress" {
    for_each = [80, 443, 8080]
    content {
      from_port   = ingress.value
      to_port     = ingress.value
      protocol    = "tcp"
      cidr_blocks = ["0.0.0.0/0"]
    }
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

JSON Structure

Dynamic blocks translate to JSON as nested objects preserving the dynamic, for_each, and content structure:

{
  "resource": {
    "aws_security_group": {
      "web": {
        "name": "web-sg",
        "dynamic": {
          "ingress": {
            "for_each": [80, 443, 8080],
            "content": {
              "from_port": "ingress.value",
              "to_port": "ingress.value",
              "protocol": "tcp",
              "cidr_blocks": ["0.0.0.0/0"]
            }
          }
        }
      }
    }
  }
}

for_each vs count

Dynamic blocks use for_each to iterate over collections. The iterator variable (ingress.value in this case) references the current element. In JSON, these references become strings.

Nested Dynamic Blocks

Dynamic blocks can be nested within other dynamic blocks for complex configurations like multi-level security group rules with conditions.

Content Block

The content sub-block defines the structure of each generated block. Its attributes can reference the iterator using <label>.key and <label>.value.