How to for_each through a list(objects) in Terraform

Terraform's for_each construct allows you to iterate through lists or maps to dynamically create resources. This is particularly useful when you need to manage multiple similar resources with different configurations.

Why Use for_each?

Using for_each simplifies your Terraform configuration by reducing repetition. Instead of defining multiple resources manually, you can define a single resource block and use for_each to create multiple instances dynamically.

Example: Iterating Through a List of Objects

Let's say you want to create multiple AWS S3 buckets with different names and tags. Here's how you can do it using for_each:

Step 1: Define the List of Objects

In your Terraform configuration, define a variable that holds the list of objects. Each object can represent a bucket's configuration:

variable "buckets" {
  default = [
    {
      name = "bucket-one"
      tags = {
        Environment = "Dev"
        Team        = "Engineering"
      }
    },
    {
      name = "bucket-two"
      tags = {
        Environment = "Prod"
        Team        = "Marketing"
      }
    }
  ]
}

Step 2: Use for_each in the Resource Block

Use the for_each argument to iterate through the list of objects and create an S3 bucket for each one:

resource "aws_s3_bucket" "example" {
  for_each = { for idx, bucket in var.buckets : bucket.name => bucket }

  bucket = each.value.name

  tags = each.value.tags
}

Explanation

• for_each: Iterates through the list of objects. The for expression converts the list into a map where the key is the bucket name.
• each.value: Refers to the current object in the iteration.
• bucket: Sets the bucket name dynamically.
• tags: Assigns tags to the bucket based on the object properties.

Step 3: Apply the Configuration

Run the following commands to apply the configuration:

terraform init
terraform apply

Terraform will create an S3 bucket for each object in the list.

Best Practices

• Use descriptive keys in your for_each maps to make your configuration easier to understand.
• Validate your input data to ensure it meets your requirements.
• Keep your Terraform code DRY (Don't Repeat Yourself) by leveraging constructs like for_each.

By using for_each, you can efficiently manage multiple resources in Terraform, making your infrastructure code more maintainable and scalable.