nixpkgs/modules/virtualisation/ec2-data.nix

# This module defines an Upstart job that obtains the SSH key and host
# name of virtual machines running on Amazon EC2, Eucalyptus and
# OpenStack Compute (Nova).

{ config, pkgs, ... }:

with pkgs.lib;
let
  options = {
    ec2.metadata = mkOption {
      type = types.bool;
      default = false;
      description = ''
        Whether to allow access to EC2 metadata.
      '';
    };
  };
in
{
  require = [options];

  systemd.services."fetch-ec2-data" =
    { description = "Fetch EC2 Data";

      wantedBy = [ "multi-user.target" ];
      before = [ "sshd.service" ];
      after = [ "network.target" ];

      path = [ pkgs.curl pkgs.iproute ];

      script =
        ''
          ip route del blackhole 169.254.169.254/32 || true

          curl="curl --retry 3 --retry-delay 0 --fail"

          echo "setting host name..."
          ${optionalString (config.networking.hostName == "") ''
            ${pkgs.nettools}/bin/hostname $($curl http://169.254.169.254/1.0/meta-data/hostname)
          ''}

          # Don't download the SSH key if it has already been injected
          # into the image (a Nova feature).
          if ! [ -e /root/.ssh/authorized_keys ]; then
              echo "obtaining SSH key..."
              mkdir -p /root/.ssh
              $curl -o /root/key.pub http://169.254.169.254/1.0/meta-data/public-keys/0/openssh-key
              if [ $? -eq 0 -a -e /root/key.pub ]; then
                  if ! grep -q -f /root/key.pub /root/.ssh/authorized_keys; then
                      cat /root/key.pub >> /root/.ssh/authorized_keys
                      echo "new key added to authorized_keys"
                  fi
                  chmod 600 /root/.ssh/authorized_keys
                  rm -f /root/key.pub
              fi
          fi

          # Extract the intended SSH host key for this machine from
          # the supplied user data, if available.  Otherwise sshd will
          # generate one normally.
          $curl http://169.254.169.254/2011-01-01/user-data > /root/user-data || true
          key="$(sed 's/|/\n/g; s/SSH_HOST_DSA_KEY://; t; d' /root/user-data)"
          key_pub="$(sed 's/SSH_HOST_DSA_KEY_PUB://; t; d' /root/user-data)"
          if [ -n "$key" -a -n "$key_pub" -a ! -e /etc/ssh/ssh_host_dsa_key ]; then
              mkdir -m 0755 -p /etc/ssh
              (umask 077; echo "$key" > /etc/ssh/ssh_host_dsa_key)
              echo "$key_pub" > /etc/ssh/ssh_host_dsa_key.pub
          fi

          ${optionalString (! config.ec2.metadata) ''
          # Since the user data is sensitive, prevent it from being
          # accessed from now on.
          ip route add blackhole 169.254.169.254/32
          ''}
        '';

      serviceConfig.Type = "oneshot";
      serviceConfig.RemainAfterExit = true;
    };

  systemd.services."print-host-key" =
    { description = "Print SSH Host Key";
      wantedBy = [ "multi-user.target" ];
      after = [ "sshd.service" ];
      script =
        ''
          # Print the host public key on the console so that the user
          # can obtain it securely by parsing the output of
          # ec2-get-console-output.
          echo "-----BEGIN SSH HOST KEY FINGERPRINTS-----" > /dev/console
          ${pkgs.openssh}/bin/ssh-keygen -l -f /etc/ssh/ssh_host_dsa_key.pub > /dev/console
          echo "-----END SSH HOST KEY FINGERPRINTS-----" > /dev/console
        '';
      serviceConfig.Type = "oneshot";
      serviceConfig.RemainAfterExit = true;
    };

}