cloudinit/infrastructure.org

#+TITLE: Creating AWS Infrastructure for Common Lisp Web-Application using cloudinit && terraform
#+PROPERTY: header-args:hcl :tangle main.tf :mkdirp yes

#+begin_src python :noweb "yes"
  import os
  from collections import OrderedDict
  import yaml

  def represent_ordereddict(dumper, data):
      return dumper.represent_mapping('tag:yaml.org,2002:map', data.items())

  yaml.add_representer(OrderedDict, represent_ordereddict)

  # Define the order of keys
  key_order = [
      "local",
      "keyboard",
      "timezone",
      "groups",
      "users",
      "packages",
      "package_update",
      "package_upgrade"
  ]

  # Initialize OrderedDict with the defined keys
  cloudinit_data = OrderedDict((key, None) for key in key_order)

  <<local-settings>>
  <<timezone-setting>>
  <<groups-creation>>
  <<user-creation-configuration>>
  <<package-install>>

  # Remove any keys with None values
  cloudinit_data = OrderedDict((k, v) for k, v in cloudinit_data.items() if v is not None)

  with open("cloudinit1.yaml", 'w') as file:
      file.write("#cloud-config\n")
      yaml.dump(cloudinit_data, file, default_flow_style=False)
#+end_src

#+RESULTS:
: None

* Cloudinit
** Introduction

This document explains the structure and content of our ~cloudinit.yml~ file,
which is used to initialize our AWS EC2 instance. The code blocks in this file
can be tangled to create the final ~cloudinit.yml~ file.

** Locale and Keyboard Settings

Set the system locale and keyboard layout.

#+name: local-settings
#+begin_src python
  cloudinit_data["local"] = "en_US.UTF-8"
  cloudinit_data["keyboard"] = {"layout": "en_US.UTF-8"}
#+end_src

** Timezone Setting

Set the system timezone.

#+name: timezone-setting
#+begin_src python
  cloudinit_data["timezone"] = "Europe/Berlin"
#+end_src

** Groups Creation

Create any necessary system groups.

#+name: groups-creation
#+begin_src python
  cloudinit_data["groups"] = ["nginxgroup"]
#+end_src

** User Creation and Configuration

Create and configure users. Here we're creating two users: a system user for
Nginx and a regular user for administration.

#+name: user-creation-configuration
#+begin_src python
  def read_ssh_key(identity="id_ed25519"):
      home_dir = os.path.expanduser("~")
      ssh_file_path = os.path.join(home_dir, ".ssh", f"{identity}.pub")

      try:
          with open(ssh_file_path, "r") as ssh_file:
              return ssh_file.readline().strip()
      except FileNotFoundError:
          print(f"SSH key file not found: {ssh_file_path}")
          return None

  cloudinit_data["users"] = [{"name": "nginxuser",
                              "system": "true",
                              "shell": "/usr/sbin/nologin",
                              "groups": ["nginxgroup"],
                              "sudo": "null"},
                             {"name": "cl",
                              "groups": ["users", "admin"],
                              "sudo": "ALL=(ALL) NOPASSWD:ALL",
                              "shell": "/bin/bash",
                              "ssh_authorized_keys": [read_ssh_key()]}]
#+end_src

** Package Installation

Install necessary packages.

#+name: package-install
#+begin_src python :results none
  cloudinit_data["packages"] = ["detachtty", "fail2ban", "ufw", "unattended-upgrades", "sbcl", "mosh", "tmux", "git", "nginx", "certbot", "python3-certbot-nginx", "build-essential", "libzstd-dev", "libsqlite3-dev", "sqlite3", "curl", "wget"]
  cloudinit_data["package_update"] = True
  cloudinit_data["package_upgrade"] = True
#+end_src

** File Writing

Write configuration files and scripts to the instance.

#+BEGIN_SRC yaml
write_files:
#+END_SRC

*** Automatic Upgrades Configuration
#+BEGIN_SRC yaml
  - path: /etc/apt/apt.conf.d/20auto-upgrades
    content: |
      APT::Periodic::Update-Package-Lists "1";
      APT::Periodic::Download-Upgradeable-Packages "1";
      APT::Periodic::AutocleanInterval "7";
      APT::Periodic::Unattended-Upgrade "1";
#+END_SRC

*** SSH Configuration
#+BEGIN_SRC yaml
  - path: /etc/ssh/sshd_config
    content: |
      Include /etc/ssh/sshd_config.d/*.conf
      MaxAuthTries 3
      AuthorizedKeysFile .ssh/authorized_keys
      PasswordAuthentication no
      AuthenticationMethods publickey
      PubkeyAuthentication yes
      PermitRootLogin no
      KbdInteractiveAuthentication no
      UsePAM yes
      AllowAgentForwarding no
      AllowTcpForwarding yes
      X11Forwarding no
      PrintMotd no
      KexAlgorithms curve25519-sha256@libssh.org
      Ciphers chacha20-poly1305@openssh.com
      MACs hmac-sha2-512-etm@openssh.com
      AcceptEnv LANG LC_*
      Subsystem sftp /usr/lib/openssh/sftp-server
      AllowUsers cl
#+END_SRC

*** Fail2Ban Configuration
#+BEGIN_SRC yaml
  - path: /etc/fail2ban/jail.local
    content: |
      [DEFAULT]
      bantime = 3600
      findtime = 600
      maxretry = 3
      banaction = ufw

      [sshd]
      enabled = true
      port = 22
      logpath = /var/log/auth.log

      [sshd-ddos]
      filter = sshd
      enabled = true
      port = ssh
      logpath = /var/log/auth.log
      maxretry = 5
      bantime = 600

      [nginx-http-auth]
      enabled = true
      action = ufw
      logpath = /var/log/nginx/error.log
      maxretry = 6
      bantime = 3600
      findtime = 600
#+END_SRC

*** Nginx Configuration
#+BEGIN_SRC yaml
  - path: /etc/nginx/nginx.conf
    content: |
      user nginxuser;
      worker_processes auto;
      pid /run/nginx.pid;
      include /etc/nginx/modules-enabled/*.conf;
      events {
        worker_connections 768;
      }
      http {
        sendfile on;
        tcp_nopush on;
        types_hash_max_size 2048;
        include /etc/nginx/mime.types;
        default_type application/octet-stream;
        ssl_protocols TLSv1.2 TLSv1.3;
        ssl_prefer_server_ciphers on;
        log_format csv '$time_iso8601,$remote_addr,$remote_user,"$request",$status,$body_bytes_sent,$http_referer,"$http_user_agent"';
        access_log /var/log/nginx/access.csv csv;
        error_log /var/log/nginx/error.log;
        gzip on;
        server_tokens off;
        include /etc/nginx/conf.d/*.conf;
        include /etc/nginx/sites-enabled/*;
      }
#+END_SRC

*** Nginx Reverse Proxy Configuration
#+BEGIN_SRC yaml
  - path: /etc/nginx/sites-available/reverse-proxy.conf
    content: |
      server {
        listen 80;
        server_name survey.metalisp.dev;
        return 301 https://$host$request_uri;
      }

      server {
        listen 443 ssl;
        server_name survey.metalisp.dev;

        ssl_certificate /etc/letsencrypt/live/survey.metalisp.dev/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/survey.metalisp.dev/privkey.pem;
        include /etc/letsencrypt/options-ssl-nginx.conf;
        ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;

        location / {
          proxy_pass http://localhost:8080;
          proxy_set_header Host $host;
          proxy_set_header X-Real-IP $remote_addr;
          proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
          proxy_set_header X-Forwarded-Proto $scheme;
        }
      }
#+END_SRC

*** Git Configuration Script
#+BEGIN_SRC yaml
  - path: /home/cl/setup_git.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      git config --global user.email "marcus.kammer@mailbox.org"
      git config --global user.name "Marcus Kammer"
      git config --global init.defaultBranch main
      git config --global pull.rebase true
#+END_SRC

*** Repository Setup Script
#+BEGIN_SRC yaml
  - path: /home/cl/setup_repos.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      git clone https://github.com/slime/slime.git ~/slime && cd ~/slime && git checkout v2.30
#+END_SRC

*** User Setup Script
#+BEGIN_SRC yaml
  - path: /home/cl/setup_user_all.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      /bin/bash /home/cl/setup_git.sh
      /bin/bash /home/cl/setup_repos.sh
      ssh-keygen -t ed25519 -C 'survey.metalisp' -f ~/.ssh/id_ed25519 -N ''
      mkdir -p ~/www/survey/docs/
#+END_SRC

*** OpenAI Bot Blocking Script
#+BEGIN_SRC yaml
  - path: /home/cl/openai_block_access.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      file="/tmp/out.txt.$$"
      wget -q -O "$file" https://openai.com/gptbot-ranges.txt 2>/dev/null

      while IFS= read -r cidr
      do
          sudo ufw deny proto tcp from $cidr to any port 80
          sudo ufw deny proto tcp from $cidr to any port 443
      done < "$file"
      [ -f "$file" ] && rm -f "$file"
#+END_SRC

*** Tmux Configuration
#+BEGIN_SRC yaml
  - path: /home/cl/.tmux.conf
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      set -g default-terminal "screen-256color"
      unbind C-b
      set -g prefix C-a
      bind C-a send-prefix
      set -g mouse on
      bind -n M-Left select-pane -L
      bind -n M-Right select-pane -R
      bind -n M-Up select-pane -U
      bind -n M-Down select-pane -D
      bind -n M-h resize-pane -L 2
      bind -n M-j resize-pane -D 2
      bind -n M-k resize-pane -U 2
      bind -n M-l resize-pane -R 2
      bind | split-window -h
      bind - split-window -v
      bind r source-file ~/.tmux.conf
      unbind ^A
      bind ^A select-pane -t :.+
      set -g history-limit 50000
      set -g status-bg colour235
      set -g status-fg colour137
      set -g status-interval 5
      set -g status-left "#[fg=colour81]#H "
      set -g status-right "#[fg=colour137]#(date '+%Y-%m-%d %H:%M')"
      setw -g window-status-current-style fg=colour125,bg=colour235,bold
      set -g pane-border-style fg=colour238
      set -g pane-active-border-style fg=colour81
      set -g message-style fg=colour166,bg=colour235
      setw -g window-status-current-format "#[bold,fg=colour81]#I:#W#F"
      setw -g window-status-format "#[fg=colour137]#I:#W#F"
#+END_SRC

*** SQL Access Logs Script
#+BEGIN_SRC yaml
  - path: /home/cl/access_logs.sql
    owner: 'cl:cl'
    defer: True
    content: |
      .mode csv
      CREATE TABLE IF NOT EXISTS access_logs (
        timestamp TEXT,
        ip_address TEXT,
        remote_user TEXT,
        request TEXT,
        status_code INTEGER,
        body_bytes_sent INTEGER,
        http_referer TEXT,
        http_user_agent TEXT
      );
      .import '/var/log/nginx/access.csv' access_logs
#+END_SRC

*** Pi-hole UFW Setup Script
#+BEGIN_SRC yaml
  - path: /home/cl/pihole_set_ufw.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      sudo ufw allow 80/tcp
      sudo ufw allow 53/tcp
      sudo ufw allow 53/udp
      sudo ufw allow 67/tcp
      sudo ufw allow 67/udp
      sudo ufw allow 546:547/udp
#+END_SRC

*** SBCL System-wide Configuration
#+BEGIN_SRC yaml
  - path: /etc/sbclrc
    content: |
      (let ((script (and (second *posix-argv*)
                         (probe-file (second *posix-argv*)))))
         (when script
            (set-dispatch-macro-character #\# #\!
                                          (lambda (stream char arg)
                                             (declare (ignore char arg))
                                             (read-line stream)))
            (setf *invoke-debugger-hook*
                  (lambda (condition hook)
                    (declare (ignore hook))
                    (format *error-output* "Error: ~A~%" condition)
                    (quit)))
            (load script)
            (quit)))

      (defun print-condition-hook (condition hook)
        (declare (ignore hook))
        (princ condition)
        (clear-input)
        (abort))

      *debugger-hook*

      (setf *debugger-hook* #'print-condition-hook)
#+END_SRC

*** SBCL User Configuration
#+BEGIN_SRC yaml
  - path: /home/cl/.sbclrc
    owner: 'cl:cl'
    defer: True
    content: |
      (sb-ext:set-sbcl-source-location #P"~/sbcl/")
#+END_SRC

*** SBCL Setup Script
#+BEGIN_SRC yaml
  - path: /home/cl/lisp_01_setup_sbcl.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      set -e
      sudo apt update
      sudo apt install -y sbcl git libzstd-dev
      git clone --branch sbcl-2.4.7 git://git.code.sf.net/p/sbcl/sbcl ~/sbcl
      cd sbcl
      sh make.sh --fancy
      sudo sh install.sh
      sudo apt remove sbcl -y
      cd ~/ && sbcl --version
#+END_SRC

*** Quicklisp Setup Script
#+BEGIN_SRC yaml
  - path: /home/cl/lisp_02_setup_quicklisp.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      sudo apt install -y libev4 libsqlite3-dev
      curl https://beta.quicklisp.org/quicklisp.lisp -o ~/quicklisp.lisp
      sbcl --noinform --load quicklisp.lisp --eval "(quicklisp-quickstart:install)" --eval "(ql-util:without-prompting (ql:add-to-init-file))" --non-interactive
      sbcl --noinform --eval "(ql:quickload '(:hunchentoot :spinneret))" --non-interactive
#+END_SRC
*** Swank Faster Loading Script
#+BEGIN_SRC yaml
  - path: /home/cl/lisp_03_load_swank_faster.lisp
    owner: 'cl:cl'
    defer: True
    content: |
      (mapc 'require '(sb-bsd-sockets sb-posix sb-introspect sb-cltl2 asdf))
      (ql:quickload '(:hunchentoot :spinneret))
      (save-lisp-and-die "sbcl.core-for-slime")
#+END_SRC

*** Script to Run Swank Faster Loading
#+BEGIN_SRC yaml
  - path: /home/cl/lisp_03_load_swank_faster.sh
    owner: 'cl:cl'
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash
      sbcl --noinform --noprint --load ~/lisp_03_load_swank_faster.lisp
#+END_SRC

*** Emacs Build Script
#+BEGIN_SRC yaml
  - path: /home/cl/emacs_build.sh
    owner: cl:cl
    permissions: '0755'
    defer: True
    content: |
      #!/bin/bash

      git clone git@git.sr.ht:~marcuskammer/emacs.d-lisp ~/.emacs.d/

      sudo apt update
      sudo apt install -y build-essential git autoconf texinfo libncurses-dev libgnutls28-dev libjansson-dev libgccjit-13-dev pkg-config zlib1g-dev libtree-sitter-dev libxml2-dev

      git clone git://git.sv.gnu.org/emacs.git ~/emacs-src && cd emacs-src

      git checkout emacs-29

      ./autogen.sh

      ./configure --without-xpm --without-jpeg --without-png --without-gif --without-tiff --without-xpm --without-rsvg --without-webp --without-lcms2 --without-cairo --without-gpm --with-json --with-native-compilation --with-tree-sitter

      make -j$(nproc)

      sudo make install
#+END_SRC

*** Emacs Service Configuration
#+BEGIN_SRC yaml
  - path: /home/cl/.config/systemd/user/emacs.service
    owner: cl:cl
    defer: True
    content: |
      [Unit]
      Description=Emacs text editor
      Documentation=info:emacs man:emacs(1) https://gnu.org/software/emacs/

      [Service]
      Type=forking
      ExecStart=emacs --daemon
      ExecStop=emacsclient --eval "(kill-emacs)"
      Environment=SSH_AUTH_SOCK=%t/keyring/ssh
      Restart=on-failure

      [Install]
      WantedBy=default.target
#+END_SRC

** Run Commands

Execute commands after the instance has been set up.

#+BEGIN_SRC yaml
runcmd:
  - curl https://ssl-config.mozilla.org/ffdhe2048.txt > /etc/letsencrypt/ssl-dhparam.pem
  - ln -s /etc/nginx/sites-available/reverse-proxy.conf /etc/nginx/sites-enabled/
  - rm /etc/nginx/sites-enabled/default
  - systemctl reload nginx
  - ufw allow 'Nginx Full'
  - ufw default deny incoming
  - ufw default allow outgoing
  - ufw allow 22/tcp
  - ufw allow mosh
  - ufw enable
  - systemctl enable fail2ban && systemctl start fail2ban
  - systemctl restart sshd
  - sudo -u cl /bin/bash /home/cl/setup_user_all.sh
#+END_SRC

** SSL Setup Script

Add a script to set up SSL certificates manually when needed.

#+BEGIN_SRC yaml
write_files:
  - path: /home/cl/setup_ssl.sh
    owner: cl:cl
    permissions: '0755'
    content: |
      #!/bin/bash
      # This script sets up SSL certificates using Let's Encrypt

      # Check if domain is provided
      if [ $# -eq 0 ]; then
          echo "Please provide a domain name as an argument."
          exit 1
      fi

      DOMAIN=$1

      # Install certbot if not already installed
      if ! command -v certbot &> /dev/null; then
          sudo apt update
          sudo apt install -y certbot python3-certbot-nginx
      fi

      # Obtain SSL certificate
      sudo certbot --nginx -d $DOMAIN --non-interactive --agree-tos --email your-email@example.com --redirect

      # Setup auto-renewal
      (crontab -l 2>/dev/null; echo "0 12 * * * /usr/bin/certbot renew --quiet") | crontab -

      echo "SSL certificate has been set up for $DOMAIN"

runcmd:
  # Install certbot
  - apt update
  - apt install -y certbot python3-certbot-nginx
#+END_SRC

** Conclusion
This concludes the documentation for our ~cloudinit.yml~ file. To generate the actual YAML file from this Org document, you can use the following Emacs command:

~C-c C-v t~

Or in an Org-mode babel shell block:

#+BEGIN_SRC emacs-lisp :results silent
(org-babel-tangle)
#+END_SRC

This will create the ~cloudinit.yml~ file with all the code blocks in the correct order and with proper indentation.

Remember to review the generated YAML file to ensure all indentations are correct, as YAML is sensitive to indentation.
* Terraform and AWS
** Introduction

This tutorial will guide you through creating a ~main.tf~ file for setting up
basic AWS infrastructure using Terraform. We'll explain each resource, why it's
necessary, and the order in which they should be created. The code blocks in
this file can be tangled to create the final ~main.tf~ file.

** Virtual Private Cloud (VPC)

We start with creating a VPC, which is a virtual network dedicated to your AWS
account. It's the foundation for all other resources.

#+BEGIN_SRC hcl
resource "aws_vpc" "mlsurvey_vpc" {
  cidr_block           = "10.0.0.0/16"
  enable_dns_hostnames = true
  enable_dns_support   = true
  tags = {
    Name = "ml-survey-vpc"
  }
}
#+END_SRC

This VPC:
- Has a CIDR block of 10.0.0.0/16, allowing for up to 65,536 IP addresses.
- Enables DNS hostnames and support, which are necessary for EC2 instances to have DNS names.

** Subnet

Next, we create a subnet within our VPC. Subnets allow you to partition your
network to group resources together.

#+BEGIN_SRC hcl
resource "aws_subnet" "mlsurvey_public_subnet" {
  vpc_id                  = aws_vpc.mlsurvey_vpc.id
  cidr_block              = "10.0.1.0/24"
  map_public_ip_on_launch = true
  availability_zone       = "eu-central-1a"
  tags = {
    Name = "ml-survey-public"
  }
}
#+END_SRC

This subnet:
- Is associated with our VPC.
- Has a CIDR block of 10.0.1.0/24, allowing for up to 256 IP addresses.
- Automatically assigns public IP addresses to instances launched in it.
- Is located in the eu-central-1a availability zone.

** Internet Gateway
An Internet Gateway allows communication between your VPC and the internet.

#+BEGIN_SRC hcl
resource "aws_internet_gateway" "mlsurvey_internet_gateway" {
  vpc_id = aws_vpc.mlsurvey_vpc.id
  tags = {
    Name = "ml-survey-igw"
  }
}
#+END_SRC

This Internet Gateway is attached to our VPC, enabling internet access for
resources within the VPC.

** Route Table

A route table contains a set of rules (routes) that determine where network
traffic is directed.

#+BEGIN_SRC hcl
resource "aws_route_table" "mlsurvey_public_rt" {
  vpc_id = aws_vpc.mlsurvey_vpc.id
  tags = {
    Name = "ml-survey-rt"
  }
}
#+END_SRC

This route table is associated with our VPC and will contain the rules for
routing traffic.

** Route

We add a route to our route table to direct internet-bound traffic to the
Internet Gateway.

#+BEGIN_SRC hcl
resource "aws_route" "mlsurvey_default_route" {
  route_table_id         = aws_route_table.mlsurvey_public_rt.id
  destination_cidr_block = "0.0.0.0/0"
  gateway_id             = aws_internet_gateway.mlsurvey_internet_gateway.id
}
#+END_SRC

This route sends all traffic (0.0.0.0/0) to the Internet Gateway, allowing resources in our VPC to access the internet.

** Route Table Association
We associate our route table with the subnet to apply the routing rules.

#+BEGIN_SRC hcl
resource "aws_route_table_association" "mlsurvey_public_assoc" {
  subnet_id      = aws_subnet.mlsurvey_public_subnet.id
  route_table_id = aws_route_table.mlsurvey_public_rt.id
}
#+END_SRC

This association ensures that the routing rules apply to resources in our subnet.

** Security Group
A security group acts as a virtual firewall for your instance to control inbound and outbound traffic.

#+BEGIN_SRC hcl
resource "aws_security_group" "mlsurvey_sg" {
  name        = "ml-survey-sg"
  description = "ml-survey security group"
  vpc_id      = aws_vpc.mlsurvey_vpc.id

  ingress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}
#+END_SRC

This security group allows all inbound and outbound traffic. In a production environment, you would typically restrict this for better security.

** Key Pair
A key pair is used to securely SSH into your EC2 instances.

#+BEGIN_SRC hcl
resource "aws_key_pair" "mlsurvey_auth" {
  key_name   = "ml-survey-key"
  public_key = file("~/.ssh/ml-survey-key.pub")
}
#+END_SRC

This resource uploads your public key to AWS, allowing you to use the corresponding private key to SSH into instances.

** EC2 Instance
Finally, we create an EC2 instance, which is a virtual server in Amazon's Elastic Compute Cloud (EC2) for running applications.

#+BEGIN_SRC hcl
resource "aws_instance" "dev_node" {
  instance_type               = "t2.micro"
  ami                         = data.aws_ami.server_ami.id
  key_name                    = aws_key_pair.mlsurvey_auth.id
  vpc_security_group_ids      = [aws_security_group.mlsurvey_sg.id]
  subnet_id                   = aws_subnet.mlsurvey_public_subnet.id
  user_data                   = data.cloudinit_config.config.rendered
  user_data_replace_on_change = true
  tags = {
    Name = "dev-node"
  }
}
#+END_SRC

This EC2 instance:
- Uses the t2.micro instance type.
- Uses the AMI specified in the ~aws_ami~ data source.
- Uses the key pair we created for SSH access.
- Is placed in our VPC and subnet.
- Has the security group we created applied to it.
- Uses the cloud-init configuration we specified.

** Output
Lastly, we add an output to display the public IP of our instance.

#+BEGIN_SRC hcl
  output "dev_node_public_ip" {
    value = aws_instance.dev_node.public_ip
  }
#+END_SRC

This output will be displayed after Terraform applies the configuration, making
it easy to find the IP address of your new instance.
** Conclusion

By tangling all these code blocks, you'll have a complete ~main.tf~ file that
sets up a basic AWS infrastructure. The resources are created in a logical
order, with each building upon the previous ones to create a fully functional
network and compute environment in AWS.

Remember to also create the necessary ~datasource.tf~ and ~providers.tf~ files
to complete your Terraform configuration.

To tangle this file and create ~main.tf~, you can use the following Emacs
command: ~C-c C-v t~