HCL Language - 39 - Dynamic Block Declarations

Exploring Dynamic Block Declarations in HCL

Dynamic block declarations are a powerful feature of the HashiCorp Configuration Language (HCL) that enable the dynamic creation of multiple blocks within a configuration. This capability adds flexibility and expressiveness to your HCL code, allowing you to create complex configurations with ease. In this discussion, we’ll delve into the concept of dynamic block declarations, their significance, and how to use them effectively.

The Significance of Dynamic Blocks

Dynamic blocks in HCL offer several benefits, making them essential for managing configurations:

Abstraction: Dynamic blocks allow you to abstract and represent complex configurations more concisely, improving the readability of your code.
Flexibility: They provide flexibility in handling variable numbers of blocks or dynamically generated configurations, adapting to different requirements and scenarios.
Reduced Repetition: Dynamic blocks help eliminate repetitive code, as you can create similar blocks with varying attributes in a more efficient way.
Parameterization: You can parameterize dynamic blocks, making it easy to customize and scale configurations by passing variables and values.

Dynamic Blocks Syntax

Dynamic blocks in HCL follow a specific syntax that allows you to define a block type and then generate multiple instances of that block with varying attributes. Here’s the basic syntax for dynamic block declarations:

Dynamic Block Syntax


dynamic "block_type" {
  for_each = var.collection
  content {
    attribute1 = value1
    attribute2 = value2
    # ... additional attributes
  }
}

The “block_type” represents the type of block you want to create dynamically. “for_each” is used to iterate over a collection of values, and for each value, a new instance of the block is generated with its attributes specified within the “content” block.

Dynamic Block Example

Let’s take a practical example of using dynamic block declarations in HCL to create multiple AWS S3 buckets with varying settings. In this example, we’ll use a variable to define a list of bucket names.

Example of Dynamic Block Declarations


variable "bucket_names" {
  type    = list(string)
  default = ["bucket1", "bucket2", "bucket3"]
}

resource "aws_s3_bucket" "example" {
  for_each = toset(var.bucket_names)

  dynamic "acl" {
    for_each = {
      private   = "private"
      public-read = "public-read"
    }
    content {
      grant = acl.value
    }
  }
}

In this example, we use dynamic block declarations to create multiple AWS S3 buckets, with the bucket names provided in the “bucket_names” variable. We also define dynamic blocks for access control lists (ACLs) to specify the grant settings for each bucket.

Benefits of Dynamic Blocks

Dynamic blocks in HCL offer various advantages for managing complex configurations and infrastructure as code (IaC) projects:

Scalability: Dynamic blocks make it easy to scale configurations by adding or modifying instances with minimal code changes, especially when dealing with a variable number of resources.
Readability: They enhance code readability by simplifying complex configurations, reducing repetition, and encapsulating similar attributes within blocks.
Parameterization: Dynamic blocks are highly parameterizable, allowing you to customize configurations with variables and attributes.
Reusability: You can reuse dynamic block configurations across different parts of your code or in various projects, reducing redundancy.

Conclusion

Dynamic block declarations in HCL provide a flexible and powerful mechanism for creating multiple instances of blocks within your configuration. They significantly enhance code readability, scalability, and parameterization, making them a valuable tool for managing complex configurations and infrastructure projects efficiently.

HCL Language – 39 – Dynamic Block Declarations