Unable to mount an EFS volume on an ECS task definition container using Terraform

Using terraform, I am trying to attach an EFS volume to a container. I would specify a folder to mount on rather than the root path. I have tried everything but no matter what I do, the root_directory option seems to be ignored.

This is my task definition snippet:

resource "aws_ecs_task_definition" "ecs_task_def" {
  family                = "application"
  container_definitions = jsonencode([
    {
      ...
    },
    {
      name : "redis",
      mountPoints = [
        {
          "readOnly" : null,
          "containerPath" : "/bitnami/redis/data",
          "sourceVolume" : "efs"
        }
      ],
      ...
    }
  ])
  ...

  volume {
    name = "efs"

    efs_volume_configuration {
      file_system_id     = var.ecs_efs_filesystem_id
      transit_encryption = "DISABLED"
      root_directory     = "/some/path/here"
      authorization_config {
        iam = "DISABLED"
      }
    }
  }
}

No matter what I try to do, the container always mounts on the at the root. I have tried creating the folders myself but nothing changes. No matter what I do, I always end up with this:

I would appreciate it if someone could tell where I could be going wrong. Thank you.