I've been going through answers to similar questions on this StackExchange and on StackOverflow and reading through documentations all day ...

Here's the .tf file I'm executing:

# defines the AWS provider
provider "aws" {
  # credentials path: ~/.aws/credentials
  profile = var.aws_profile
}
resource "aws_key_pair" "key_pair" {
  # variable's default value: "id_rsa"
  key_name   = var.aws_key_pair_name
  # variable's default value: public key of "id_rsa"
  public_key = var.aws_key_pair_public
}
resource "aws_security_group" "security_group" {
  ingress {
    from_port = 22
    to_port = 22
    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"]
  }
  tags = {
    # variable's default value: "security-group-1"
    Name = var.aws_security_group_tags_name
  }
}
resource "aws_instance" "instance" {
  # variable's default value: ID of the Ubuntu AMI
  ami = var.aws_instance_ami
  # variable's default value: "t2.micro"
  instance_type = var.aws_instance_type
  associate_public_ip_address  = true
  key_name = aws_key_pair.key_pair.key_name
  vpc_security_group_ids = [aws_security_group.security_group.id]
  tags = {
    # variable's default value: "ec2-instance-1"
    Name = var.aws_instance_tags_name
  }
}
resource "null_resource" "instance" {
  provisioner "remote-exec" {
    connection  {
      type = "ssh"
      host = aws_instance.instance.public_ip
      # variable's default value: "ubuntu", Ubuntu AMI's default system user account
      user = var.aws_instance_user_name
      # variable's default value: "~/.ssh/id_rsa"
      # the path to the public key provided to aws_key_pair.key_pair
      private_key = file(var.aws_key_pair_private_path)
      timeout = "20s"
    }
    inline = ["echo 'remote-exec message'"]
  }
  provisioner "local-exec" {
    command = "echo 'local-exec message'"
  }
}

It's returning the following error:

aws_instance.instance (remote-exec): Connecting to remote host via SSH...
aws_instance.instance (remote-exec):   Host: 54.82.23.158
aws_instance.instance (remote-exec):   User: ubuntu
aws_instance.instance (remote-exec):   Password: false
aws_instance.instance (remote-exec):   Private key: true
aws_instance.instance (remote-exec):   Certificate: false
aws_instance.instance (remote-exec):   SSH Agent: true
aws_instance.instance (remote-exec):   Checking Host Key: false
aws_instance.instance (remote-exec):   Target Platform: unix
aws_instance.instance: Still creating... [1m0s elapsed]
╷
│ Error: remote-exec provisioner error
│ 
│   with aws_instance.instance,
│   on main.tf line 63, in resource "aws_instance" "instance":
│   63:   provisioner "remote-exec" {
│ 
│ timeout - last error: SSH authentication failed ([email protected]:22): ssh: handshake failed: ssh: unable to
│ authenticate, attempted methods [none publickey], no supported methods remain

What am I missing? Are any parts of my code redundant?