Errata

It might worth to mention that the first time `terraform apply` is used after output variable is declared (with no changes to any resources) the question to save new output value to the Terraform state is appeared.

```
$ terraform apply
aws_security_group.instance: Refreshing state... [id=sg-0942e8axxxxxxxxxx]
aws_instance.example: Refreshing state... [id=i-085601cxxxxxxxxxx]

Changes to Outputs:
+ public_ip = "16.xx.xx.xx"

You can apply this plan to save these new output values to the Terraform state, without changing any real infrastructure.

Do you want to perform these actions?
Terraform will perform the actions described above.
Only 'yes' will be accepted to approve.

Enter a value: yes


Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

public_ip = "16.xx.xx.xx"
```

Note from the Author or Editor:
Yes, it's a good idea to clarify this, thanks!

It seems that for terraform version 1.4.0, to copy the Terraform state back to local disk after removing the `backend` configuration from `main.tf`, it is necessary to run the mentioned command with `-migrate-state` flag, like: `terraform init -migrate-state`

Note from the Author or Editor:
You're right, the "-migrate-state" flag is now necessary to move the state.

Due to aws no longer accepting resource aws_launch_configuration, switched to aws_launch_template:
resource "aws_launch_template" "example" {
# image_id = "ami-0fb653ca2d3203ac1"
image_id = "ami-0efc43a4067fe9a3e"
instance_type = "t2.micro"


user_data = base64encode(
<<-EOF
#!/bin/bash
echo "Hello, World" > index.html
nohup busybox httpd -f -p ${var.server_port} &
EOF
)


# Required when using a launch configuration with an auto scaling group.
lifecycle {
create_before_destroy = true
}
security_group_names = [aws_security_group.instance.id]

}
aws_autoscaling_group.example: Creating...
╷
│ Error: creating Auto Scaling Group (terraform-20250328181831484400000001): operation error Auto Scaling: CreateAutoScalingGroup, https response error StatusCode: 400, RequestID: 75dcef72-779b-4f1c-a164-6754a94ca304, api error ValidationError: You must use a valid fully-formed launch template. The parameter groupName cannot be used with the parameter subnet
│
│ with aws_autoscaling_group.example,
│ on main.tf line 11, in resource "aws_autoscaling_group" "example":
│ 11: resource "aws_autoscaling_group" "example" {


here is the complete code from chapter 2, 3rd edition: Deploying a cluster of webservers:
provider "aws" {
region = "us-east-2"
}

resource "aws_autoscaling_group" "example" {
depends_on = [aws_launch_template.example]
lifecycle {
create_before_destroy = true
}
launch_template {
id = aws_launch_template.example.id
version = "$Latest"
}
vpc_zone_identifier = data.aws_subnets.default.ids

target_group_arns = [aws_lb_target_group.asg.arn]
health_check_type = "ELB"

max_size = 10
min_size = 2
tag {
key = "Name"
value = "terraform-asg-example-run"
propagate_at_launch = true
}
}

resource "aws_launch_template" "example" {
# image_id = "ami-0fb653ca2d3203ac1"
image_id = "ami-0efc43a4067fe9a3e"
instance_type = "t2.micro"


user_data = base64encode(
<<-EOF
#!/bin/bash
echo "Hello, World" > index.html
nohup busybox httpd -f -p ${var.server_port} &
EOF
)


# Required when using a launch configuration with an auto scaling group.
lifecycle {
create_before_destroy = true
}
security_group_names = [aws_security_group.instance.id]

}

/*
resource "aws_launch_configuration" "example" {
image_id = "ami-0fb653ca2d3203ac1"
instance_type = "t2.micro"


user_data = <<-EOF
#!/bin/bash
echo "Hello, World" > index.html
nohup busybox httpd -f -p ${var.server_port} &
EOF
# Required when using a launch configuration with an auto scaling group.
lifecycle {
create_before_destroy = true
}
security_groups = [aws_security_group.instance.id]

}
*/

resource "aws_security_group" "instance" {
name = "terraform-example-instance"
ingress {
from_port = var.server_port
to_port = var.server_port
protocol = "tcp"
cidr_blocks = ["0.0.0.0/0"]
}
}

data "aws_vpc" "default" {
default = true
}

data "aws_subnets" "default" {
filter {
name = "vpc-id"
values = [data.aws_vpc.default.id]
}
}

resource "aws_lb" "example" {
name = "terraform-asg-example"
load_balancer_type = "application"
subnets = data.aws_subnets.default.ids
security_groups = [aws_security_group.alb.id]
}

# define listeners for the resource.aws_lb.example
resource "aws_lb_listener" "http" {
load_balancer_arn = aws_lb.example.arn
port = 80
protocol = "HTTP"
# By default, return a simple 404 page
default_action {
type = "fixed-response"

fixed_response {
content_type = "text/plain"
message_body = "404: page not found"
status_code = "404"
}
}
}

# by default all AWS resources including ALBs, don't allow any incoming or outgoing traffic
# so you need to create a new security group specifically for the ALB. This sg should allow
# incoming requests on port 80 so that you can access the load balancer over HTTP, and allow
# outgoing requests on all ports so that the load balancer can perform health checks.
resource "aws_security_group" "alb" {
name = "terraform-example-alb"

# Allow inbound HTTP requests
ingress {
from_port = 80
to_port = 80
protocol = "tcp"
cidr_blocks = ["0.0.0.0/0"]
}

# Allow all outbound requests
egress {
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["0.0.0.0/0"]
}
}

resource "aws_lb_target_group" "asg" {
name = "terraform-asg-example"
port = var.server_port
protocol = "HTTP"
vpc_id = data.aws_vpc.default.id

health_check {
path = "/"
protocol = "HTTP"
matcher = "200"
interval = 15
timeout = 3
healthy_threshold = 2
unhealthy_threshold = 2

}
}

# finally tie all these resources together
resource "aws_lb_listener_rule" "asg" {
listener_arn = aws_lb_listener.http.arn
priority = 100

condition {
path_pattern {
values = ["*"]
}
}

action {
type = "forward"
target_group_arn = aws_lb_target_group.asg.arn
}
}

output "alb_dns_name" {
value = aws_lb.example.dns_name
description = "The domain name of the load balancer"
}

Note from the Author or Editor:
Yes, AWS dropped support for launch configurations in 2024. The work around is to move to launch templates. I've also documented this here: https://github.com/brikis98/terraform-up-and-running-code/issues/118#issuecomment-2476154890