auto-set-ec2-hostname chef recipe

recipes:hostname.rb

#
# Cookbook Name::ubuntu_hardened_ami
# Recipe::hostname

# Script to set hostname and /etc/hosts
template '/usr/local/bin/auto-set-ec2-hostname' do
  source 'auto-set-ec2-hostname.erb'
  owner 'root'
  group 'root'
  mode '0755'
end

case node[:platform_version]
when '16.04', '18.04'
  # use systemd in newer ubuntu releases
  # TODO this is not really tested
  template '/etc/systemd/system/auto-ec2-hostname.service' do
    source 'auto-ec2-hostname.service.erb'
    owner 'root'
    group 'root'
    mode '0644'
  end

when '14.04'
  # use sysv init in older ubuntu releases

  service 'auto-ec2-hostname' do
    supports :start => true
    action :nothing
  end

  template '/etc/init.d/auto-ec2-hostname' do
    source 'auto-ec2-hostname.init.d.erb'
    owner 'root'
    group 'root'
    mode '0755'
    notifies :enable, 'service[auto-ec2-hostname]'
    notifies :start, 'service[auto-ec2-hostname]'
  end

else
  raise "Unexpected ubuntu platform_version: #{node[:platform_version].inspect}"
end

directory '/etc/auto-hostname' do
  owner 'root'
  group 'root'
  mode '0755'
end

file '/etc/auto-hostname/domain' do
  content "aws.uscis.dhs.gov\n"
  owner 'root'
  group 'root'
  mode '0644'
end

file '/etc/auto-hostname/prefix' do
  content "hardened\n"
  owner 'root'
  group 'root'
  mode '0644'
end

templates:default:auto-ec2-hostname.init.d.erb

#!/bin/sh
### BEGIN INIT INFO
# Provides:          auto-ec2-hostname
# Required-Start:    dbus
# Required-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:
# Short-Description: Automatically set EC2 instance hostname
# Description:       Set the EC2 instance hostname  with auto-set-ec2-hostname
### END INIT INFO

PATH=/sbin:/usr/sbin:/bin:/usr/bin:/usr/local/sbin:/usr/local/bin

# shellcheck disable=SC1091
. /lib/lsb/init-functions

do_start() {
  log_begin_msg "Running auto-set-ec2-hostname"
  auto-set-ec2-hostname run
  log_end_msg $?
}

case "$1" in
  start)
    do_start
    ;;
  stop)
    # noop
    ;;
  *)
    echo "Usage: $0 start" >&2
    exit 3
    ;;
esac

templates:default:auto-ec2-hostname.service.erb

[Unit]
Description= *** Automatically set EC2 instance hostname ***
After=dbus.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/local/bin/auto-set-ec2-hostname run

[Install]
WantedBy=multi-user.target

templates:default:auto-set-ec2-hostname.erb

#!/bin/bash
set -eu

# Version 1.0

basename="$(basename "$0")"

CONFIG_DIR=/etc/auto-hostname
prefix_file="$CONFIG_DIR/prefix"
domain_file="$CONFIG_DIR/domain"

usage() {
  cat >&2 <<EOM
usage: $basename ACTION [options]

ACTION:
  run      set hostname and hosts
  dryrun   show what would be changed without making changes

Automatically set instance hostname to include EC2 instance ID. If
$prefix_file is present, use it as a prefix for the hostname. If
$domain_file is present, use it as the domain for the hostname.

When changing the hostname, also overwrite /etc/hosts with a new copy that
contains the new hostname (so sudo doesn't complain).

The resulting hostname will look like:

    PREFIX-i-abcd1234.DOMAIN

Options:

  --skip-hosts    Don't overwrite /etc/hosts

EOM
}

if [ $# -lt 1 ]; then
  usage
  exit 1
fi

case "$1" in
  run) realrun=1 ;;
  dryrun) realrun= ;;
  *)
    usage
    exit 1
    ;;
esac

shift

skip_hosts=

while [[ $# -gt 0 ]]; do
  case "$1" in
    --skip-hosts)
      skip_hosts=1
      ;;
    *)
      usage
      exit 1
  esac
  shift
done

log() {
  echo >&2 "$*"
  logger -t "$basename" "$*"
}

run() {
  log "+ $*"
  "$@"
}

saferun() {
  if [ -n "$realrun" ]; then
    log "+ $*"
    "$@"
  else
    log "(DRY RUN) + $*"
  fi
}
safelog() {
  if [ -n "$realrun" ]; then
    log "$*"
  else
    log "(DRY RUN) $*"
  fi
}

safelog "Starting up"

prefix=
domain=

if [ -e "$prefix_file" ]; then
    prefix="$(cat "$prefix_file")"
fi

if [ -e "$domain_file" ]; then
    domain="$(cat "$domain_file")"
fi

if [ -r /var/lib/cloud/data/instance-id ]; then
  instance_id="$(cat /var/lib/cloud/data/instance-id)"
  log "Found instance ID $instance_id from /var/lib/cloud/data/instance-id"
else
  instance_id="$(run curl -sSf http://169.254.169.254/latest/meta-data/instance-id)"
fi

# $prefix-$instance_id.$domain

name="$instance_id"

if [ -n "$prefix" ]; then
  name="$prefix-$name"
fi

if [ -n "$domain" ]; then
  name="$name.$domain"
fi

cur_hostname="$(hostname)"
if [ "$cur_hostname" = "$name" ]; then
  log "Hostname is already set to $name"
  exit
fi

safelog "Setting hostname to '$name'"
saferun hostnamectl set-hostname "$name"

if [ -z "$skip_hosts" ] && ! grep "$name" /etc/hosts >/dev/null; then
  safelog "Replacing /etc/hosts"
  if [ -n "$realrun" ]; then
    run cat > /etc/hosts <<EOM
# This file was first created by $basename on $(date "+%F %T")
127.0.1.1 $name
127.0.0.1 localhost

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
EOM
  fi
fi

log 'All done'

# vim: set ft=sh :