Appendix: sandbox setup

The setup referenced from Sandbox All the Things. Reproduced here so the post is self-contained.

Goal

You have an isolated environment where your tool of choice runs. It will contain a copy of your source code and the minimum amount of secrets.

We discussed the following two:

a) VM
b) docker sbx

note

If you need to have a windows environment you need to go with a).

a) is the more difficult to set up initially.

a) is the more flexible one. Both support pure "agentic coding". The VM approach enables scenarios like performance testing.

a) VM setup process

This doc chooses the following approach:

vagrant to provision and interact with a VM, default 32 GB RAM and 8 CPUs
an Ubuntu based VM
git to facilitate code exchange host <-> vm via git remotes
claude (or similar) already preinstalled on the vm
ssh to get to the VM and use a cli agent there

One time setup

Linux -> VirtualBox Linux VM

host: install virtualbox. If you want/need a different virtualization, you need to adapt the vagrant file
host: install vagrant (https://releases.hashicorp.com/vagrant/2.4.9/vagrant_2.4.9_linux_amd64.zip)
host: vagrant up in vagrant file folder, then choose your CLI tool during provisioning
host: append output of vagrant ssh-config to ~/.ssh/config and set your vagrant VM alias to something memorable like vagrant_claude (The name at the end of the first line, starting with "Host")
host: consider cleaning your git repo (git clean), then copy your source files to the VM: scp ~/your_repo vagrant_claude:/home/vagrant/coding/
host: setup git upstream to vagrant in repo: git remote add vagrant_claude vagrant_claude:/home/vagrant/coding/your_repo
host: ssh (your vagrant VM alias from SSH config) to guest
guest: remove real remote from git repo: git remote remove origin
guest: start your CLI tool and authenticate

Windows -> Hyper-V Linux VM

host: enable Hyper-V
host: install vagrant (https://releases.hashicorp.com/vagrant/2.4.9/vagrant_2.4.9_windows_amd64.msi)
host: vagrant up in vagrant file folder, then choose your CLI tool during provisioning
host: append output of vagrant ssh-config to %USERPROFILE%/.ssh/config and set your vagrant VM alias to something memorable like vagrant_claude (The name at the end of the first line, starting with "Host")
host: consider cleaning your git repo (git clean), then copy your source files to the VM: scp c:\somewhere\your_repo vagrant_claude:/home/vagrant/coding/
host: setup git upstream to vagrant in repo: git remote add vagrant_claude vagrant_claude:/home/vagrant/coding/your_repo
host: ssh (your vagrant VM alias from SSH config) to guest
guest: remove real remote from git repo: git remote remove origin
guest: start your CLI tool and authenticate

With Hyper-V you might have issues with not getting an IP. A possible solution is to create a bridge (pwsh: New-VMSwitch) and use that in config.vm.network.

For reference: ssh config example, Linux -> VirtualBox Linux VM

On a linux host: ~/.ssh/config

On a windows host: %USERPROFILE%/.ssh/config

Host vagrant_claude
  HostName 127.0.0.1
  User vagrant
  Port 2201
  UserKnownHostsFile /dev/null
  StrictHostKeyChecking no
  PasswordAuthentication no
  IdentityFile /path-to-your-vagrant-file/.vagrant/machines/default/virtualbox/private_key
  IdentitiesOnly yes
  LogLevel FATAL
  PubkeyAcceptedKeyTypes +ssh-rsa
  HostKeyAlgorithms +ssh-rsa

b) docker sbx

You will need to have a docker account to use docker sbx. But docker sbx is free to use.

Follow the docker sbx getting started guide to install it.

Do NOT use plain sbx run claude but use sbx run --clone claude.

The plain version will create a "container" (we look at the exact way it works in the academy) and volume mount your directory to it. That approach still has the issue of making non-committed files (like secrets in .env files) within the repo available to your ai tool. --clone will set your "host" as the git remote in your "container", so it really only has access to committed files.

`Vagrantfile` for Linux hosts

VirtualBox provider.

require "yaml"
require "fileutils"

vm_name = File.basename(Dir.getwd)

CHOICES_FILE = File.join(File.dirname(__FILE__), ".vagrant", "install-choices.yml")

def ask?(question)
  print "#{question} [y/N]: "
  %w[y yes].include?($stdin.gets&.strip&.downcase)
end

def load_or_ask_choices
  # Already decided once → reuse, never ask again.
  return YAML.load_file(CHOICES_FILE) if File.exist?(CHOICES_FILE)

  # Only the provisioning commands should prompt; halt/destroy/ssh/status must not.
  defaults = {
    "claude" => false,
    "dotnet" => false,
    "codex" => false
  }

  provisioning = %w[up provision reload].include?(ARGV[0])

  return defaults unless provisioning

  choices = {
    "claude" => ask?("Install claude?"),
    "dotnet" => ask?("Install dotnet?"),
    "codex" => ask?("Install codex?")
  }

  FileUtils.mkdir_p(File.dirname(CHOICES_FILE))
  File.write(CHOICES_FILE, choices.to_yaml)
  choices
end

choices = load_or_ask_choices

Vagrant.configure("2") do |config|
  config.vm.box = "bento/ubuntu-24.04"

  config.vm.network "forwarded_port", guest: 22, host: 2203, id: "ssh", auto_correct: false

  config.vm.synced_folder ".", "/vagrant", disabled: true

  config.vm.provider "virtualbox" do |vb|
    vb.memory = "32768"
    vb.cpus = 8
    vb.gui = false
    vb.name = vm_name
    vb.customize ["modifyvm", :id, "--audio", "none"]
    vb.customize ["modifyvm", :id, "--usb", "off"]
  end

  # Root-level setup
  config.vm.provision "shell",
    inline: <<-SHELL
    export DEBIAN_FRONTEND=noninteractive
    apt-get update
    apt-get install -y docker.io nodejs npm git unzip bash-completion
    usermod -aG docker vagrant
  SHELL

  # Per-user installs — runs as 'vagrant', so $HOME = /home/vagrant
  config.vm.provision "shell",
    privileged: false,
    env: {
      "INSTALL_CLAUDE" => choices["claude"].to_s,
      "INSTALL_DOTNET" => choices["dotnet"].to_s,
      "INSTALL_CODEX" => choices["codex"].to_s
    },
    inline: <<-SHELL
    if [ "$INSTALL_CLAUDE" = "true" ]; then
      curl -fsSL https://claude.ai/install.sh | bash
      echo 'export PATH="$HOME/.local/bin:$PATH"' >> ~/.bashrc
    fi

    if [ "$INSTALL_DOTNET" = "true" ]; then
      curl -fsSL https://dot.net/v1/dotnet-install.sh | bash
      echo 'export PATH="$HOME/.dotnet:$PATH"' >> ~/.bashrc
    fi

    if [ "$INSTALL_CODEX" = "true" ]; then
      curl -fsSL https://chatgpt.com/codex/install.sh | bash
    fi
  SHELL

end

`Vagrantfile` for Windows hosts

Hyper-V provider.

require "yaml"
require "fileutils"

vm_name = File.basename(Dir.getwd)

CHOICES_FILE = File.join(File.dirname(__FILE__), ".vagrant", "install-choices.yml")

def ask?(question)
  print "#{question} [y/N]: "
  %w[y yes].include?($stdin.gets&.strip&.downcase)
end

def load_or_ask_choices
  # Already decided once → reuse, never ask again.
  return YAML.load_file(CHOICES_FILE) if File.exist?(CHOICES_FILE)

  # Only the provisioning commands should prompt; halt/destroy/ssh/status must not.
  defaults = {
    "claude" => false,
    "dotnet" => false,
    "codex" => false
  }

  provisioning = %w[up provision reload].include?(ARGV[0])
  return defaults unless provisioning

  choices = {
    "claude" => ask?("Install claude?"),
    "dotnet" => ask?("Install dotnet?"),
    "codex" => ask?("Install codex?")
  }

  FileUtils.mkdir_p(File.dirname(CHOICES_FILE))
  File.write(CHOICES_FILE, choices.to_yaml)

  choices
end

choices = load_or_ask_choices

Vagrant.configure("2") do |config|
  config.vm.box = "gusztavvargadr/ubuntu-desktop-2404-lts"

  config.vm.network "public_network"

  config.vm.synced_folder ".", "/vagrant", disabled: true

  config.vm.provider "hyperv" do |hv|
    hv.vmname = vm_name
    hv.memory = 32768
    hv.cpus = 8
  end

  # Root-level setup
  config.vm.provision "shell",
    inline: <<-SHELL
      export DEBIAN_FRONTEND=noninteractive
      apt-get update
      apt-get install -y docker.io nodejs npm git unzip bash-completion curl
      usermod -aG docker vagrant
    SHELL

  # Per-user installs — runs as 'vagrant', so $HOME = /home/vagrant
  config.vm.provision "shell",
    privileged: false,
    env: {
      "INSTALL_CLAUDE" => choices["claude"].to_s,
      "INSTALL_DOTNET" => choices["dotnet"].to_s,
      "INSTALL_CODEX" => choices["codex"].to_s
    },
    inline: <<-SHELL
      if [ "$INSTALL_CLAUDE" = "true" ]; then
        curl -fsSL https://claude.ai/install.sh | bash
        echo 'export PATH="$HOME/.local/bin:$PATH"' >> ~/.bashrc
      fi

      if [ "$INSTALL_DOTNET" = "true" ]; then
        curl -fsSL https://dot.net/v1/dotnet-install.sh | bash
        echo 'export PATH="$HOME/.dotnet:$PATH"' >> ~/.bashrc
      fi

      if [ "$INSTALL_CODEX" = "true" ]; then
        curl -fsSL https://chatgpt.com/codex/install.sh | bash
      fi
    SHELL
end

The setup referenced from Sandbox All the Things. Reproduced here so the post is self-contained.​

Goal​

a) VM setup process​

One time setup​

Linux -> VirtualBox Linux VM​

Windows -> Hyper-V Linux VM​

For reference: ssh config example, Linux -> VirtualBox Linux VM​

b) docker sbx​

Vagrantfile for Linux hosts​

Vagrantfile for Windows hosts​