Amazon Linux 2023 でユーザーデータを利用して静的ホスト名を設定してみた

#!/bin/bash
set -euo pipefail

LOG_FILE="/var/log/user-data-hostname.log"
exec > >(tee -a "${LOG_FILE}" | logger -t user-data-hostname -s 2>/dev/console) 2>&1

METADATA_IP="169.254.169.254"
OVERRIDE_CFG="/etc/cloud/cloud.cfg.d/99-preserve-hostname.cfg"

echo "=== start user-data ==="

# IMDSv2 token
TOKEN="$(curl -fsS -X PUT "http://${METADATA_IP}/latest/api/token" \
  -H "X-aws-ec2-metadata-token-ttl-seconds: 21600")"

# instance-id
INSTANCE_ID="$(curl -fsS \
  -H "X-aws-ec2-metadata-token: ${TOKEN}" \
  "http://${METADATA_IP}/latest/meta-data/instance-id")"

# hostname は小文字推奨
HOSTNAME="test-server-${INSTANCE_ID}"

echo "INSTANCE_ID=${INSTANCE_ID}"
echo "HOSTNAME=${HOSTNAME}"

# --------------------------------------------------
# preserve_hostname を確認し、false なら true に更新
# --------------------------------------------------
UPDATED=0

declare -a CFG_FILES
CFG_FILES=("/etc/cloud/cloud.cfg")

shopt -s nullglob
for f in /etc/cloud/cloud.cfg.d/*.cfg; do
  CFG_FILES+=("$f")
done
shopt -u nullglob

for cfg in "${CFG_FILES[@]}"; do
  [[ -f "${cfg}" ]] || continue

  if grep -qiE '^[[:space:]]*preserve_hostname:[[:space:]]*false([[:space:]]|$)' "${cfg}"; then
    echo "found preserve_hostname: false in ${cfg} -> update to true"
    sed -i -E 's/^[[:space:]]*preserve_hostname:[[:space:]]*false([[:space:]]|$)/preserve_hostname: true/' "${cfg}"
    UPDATED=1
  fi
done

# どこにも true が無ければ override ファイルを作成
if ! grep -RqsE '^[[:space:]]*preserve_hostname:[[:space:]]*true([[:space:]]|$)' \
  /etc/cloud/cloud.cfg /etc/cloud/cloud.cfg.d 2>/dev/null; then
  echo "preserve_hostname: true not found -> create ${OVERRIDE_CFG}"
  cat > "${OVERRIDE_CFG}" <<'EOF'
preserve_hostname: true
EOF
  UPDATED=1
fi

if [[ "${UPDATED}" -eq 0 ]]; then
  echo "preserve_hostname is already true"
fi

echo "current preserve_hostname settings:"
grep -RnsE '^[[:space:]]*preserve_hostname:' /etc/cloud/cloud.cfg /etc/cloud/cloud.cfg.d 2>/dev/null || true

# --------------------------------------------------
# hostname 設定
# --------------------------------------------------
hostnamectl set-hostname "${HOSTNAME}"

echo "hostnamectl result:"
hostnamectl

echo "/etc/hostname:"
cat /etc/hostname

echo "=== end user-data ==="

$ journalctl | head -20

sh-5.2$ journalctl | head -20
Hint: You are currently not seeing messages from other users and the system.
      Users in groups 'adm', 'systemd-journal', 'wheel' can see all messages.
      Pass -q to turn off this notice.
May 02 04:53:02 test-server-i-0531a2f69fcbc4b2c sudo[1828]: ssm-user : TTY=pts/0 ; PWD=/usr/bin ; USER=root ; COMMAND=/usr/bin/nano /etc/cloud/cloud.cfg
May 02 04:53:03 test-server-i-0531a2f69fcbc4b2c sudo[1828]: pam_unix(sudo:session): session opened for user root(uid=0) by (uid=1001)
May 02 04:53:16 test-server-i-0531a2f69fcbc4b2c sudo[1828]: pam_unix(sudo:session): session closed for user root
May 02 04:59:57 test-server-i-0531a2f69fcbc4b2c sudo[2033]: ssm-user : TTY=pts/0 ; PWD=/usr/bin ; USER=root ; COMMAND=/usr/bin/nano /etc/cloud/cloud.cfg
May 02 04:59:57 test-server-i-0531a2f69fcbc4b2c sudo[2033]: pam_unix(sudo:session): session opened for user root(uid=0) by (uid=1001)
May 02 05:04:41 test-server-i-0531a2f69fcbc4b2c sudo[2033]: pam_unix(sudo:session): session closed for user root
sh-5.2$