[SOLVED] Terraform application load balancer argument is not expected here

Terraform application load balancer argument is not expected here

I currently work on an AWS architecture that looks like this : NLB -> ALB -> API Gateway -> Lambda

When I deploy my architecture, the Preserve host header attribute of the ALB is set to false. I want it set to true.

As from Terraform doc https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lb :

preserve_host_header - (Optional) Indicates whether the Application Load Balancer should preserve the Host header in the HTTP request and send it to the target without any change. Defaults to false.

Here is my Application Load Balancer configuration :

resource "aws_lb" "alb_to_api_gateway" {
      name               = "prd-alb-toapigw"
      internal           = true
      load_balancer_type = "application"
      security_groups = [var.default_SG]
      subnets    = [var.subnet_backend_a, var.subnet_backend_b]
    
      preserve_host_header = true
    
      access_logs {
        bucket  = aws_s3_bucket.elb_logs.id
        prefix  = "ALB"
        enabled = true
      }
    
      depends_on = [
       aws_s3_bucket_policy.policy_alb
      ]
    }

This configuration worked perfectly until I added the preserve_host_header argument which creates this error :

│ Error: Unsupported argument
│ 
│   on elb.tf line 12, in resource "aws_lb" "alb_to_api_gateway":
│   12:   preserve_host_header = true
│ 
│ An argument named "preserve_host_header" is not expected here.

I use Terraform v1.3.9 on linux_amd64
provider registry.terraform.io/hashicorp/archive v2.2.0
provider registry.terraform.io/hashicorp/aws v4.15.1
aws-cli/2.11.0 Python/3.11.2 Linux/5.4.0-1045-aws exe/x86_64.ubuntu.20 prompt/off

Thank you

Solution

The preserve_host_header argument was added in version 4.25.0 of the AWS provider, and you would therefore need to update the provider from 4.15.1 to >= 4.25.0.