[Let’s Encrypt] DNS-01 challenge はいいぞ

noriko

2019.08.23

DNS-01 challenge はいいぞ
certbot コマンドで出来ます。今回は Google Compute Engine と Google Cloud (GCP) DNS を使っているの前提
CentOS 7系の話

certbot コマンドで DNS-01 challenge してみる

DNS-01 challenge は TXT レコードに特定の文字列を入れて認証する方法です。最近お気に入りです。

以下のメリットがあります。

IP制限していても関係ない
ポート80や443を開けていなくていい
ロードバランサー挟んでいたり、DNSラウンドロビンしてる時に、どっちに来るかわからない時とかこのためだけの nginx の設定書く必要もなし（ぐぐったら nginx の設定でどうにかする方法がめっちゃ出てきた）
Aレコードを登録している必要もない
内部のアプリケーションで使うだけみたいな時もまぁ使えなくもないかも（オレオレ証明書でいい気もしますが）

デメリットは

DNS の設定を変更出来る必要がある（できればAPIなどで）

くらいでしょうか。あまり思い浮かびません。

とりあえず今回は Google Cloud (GCP) DNS を使ったやり方を試したいと思いますが、ヘルプを見る限り、以下のものに対応しています。

Cloudflare for DNS
CloudXNS for DNS
DigitalOcean for DNS
DNSimple for DNS
DNS Made Easy for DNS
Gehirn Infrastracture Service for DNS
Google Cloud (GCP) DNS
Linode for DNS
LuaDNS for DNS
NS1 for DNS
OVH for DNS
BIND for DNS
Route53 for DNS
Sakura Cloud for DNS

certbot プラグインの準備

今回は certbot コマンドでやってみます。

GCEのインスタンスにログインして、certbot をインストールします。

インストールは、epel 有効にしたらすぐ出来るだろうと思ったのですが、うまくいかず一旦 yum remove epel-release して、入れ直したところうまくいきました。

詳細なインストール方法は certbot の公式サイトを参照してください。

$ sudo certbot --help plugins
usage:

  certbot plugins [options]

optional arguments:
  -h, --help            show this help message and exit
  -c CONFIG_FILE, --config CONFIG_FILE
                        path to config file (default: /etc/letsencrypt/cli.ini
                        and ~/.config/letsencrypt/cli.ini)

plugins:
  Options for the "plugins" subcommand

  --init                Initialize plugins. (default: False)
  --prepare             Initialize and prepare plugins. (default: False)
  --authenticators      Limit to authenticator plugins only. (default: None)
  --installers          Limit to installer plugins only. (default: None)

plugins:
  Plugin Selection: Certbot client supports an extensible plugins
  architecture. See 'certbot plugins' for a list of all installed plugins
  and their names. You can force a particular plugin by setting options
  provided below. Running --help <plugin_name> will list flags specific to
  that plugin.

  --configurator CONFIGURATOR
                        Name of the plugin that is both an authenticator and
                        an installer. Should not be used together with
                        --authenticator or --installer. (default: Ask)
  -a AUTHENTICATOR, --authenticator AUTHENTICATOR
                        Authenticator plugin name. (default: None)
  -i INSTALLER, --installer INSTALLER
                        Installer plugin name (also used to find domains).
                        (default: None)
  --apache              Obtain and install certificates using Apache (default:
                        False)
  --nginx               Obtain and install certificates using Nginx (default:
                        False)
  --standalone          Obtain certificates using a "standalone" webserver.
                        (default: False)
  --manual              Provide laborious manual instructions for obtaining a
                        certificate (default: False)
  --webroot             Obtain certificates by placing files in a webroot
                        directory. (default: False)
  --dns-cloudflare      Obtain certificates using a DNS TXT record (if you are
                        using Cloudflare for DNS). (default: False)
  --dns-cloudxns        Obtain certificates using a DNS TXT record (if you are
                        using CloudXNS for DNS). (default: False)
  --dns-digitalocean    Obtain certificates using a DNS TXT record (if you are
                        using DigitalOcean for DNS). (default: False)
  --dns-dnsimple        Obtain certificates using a DNS TXT record (if you are
                        using DNSimple for DNS). (default: False)
  --dns-dnsmadeeasy     Obtain certificates using a DNS TXT record (if you are
                        using DNS Made Easy for DNS). (default: False)
  --dns-gehirn          Obtain certificates using a DNS TXT record (if you are
                        using Gehirn Infrastracture Service for DNS).
                        (default: False)
  --dns-google          Obtain certificates using a DNS TXT record (if you are
                        using Google Cloud (GCP) DNS). (default: False)
  --dns-linode          Obtain certificates using a DNS TXT record (if you are
                        using Linode for DNS). (default: False)
  --dns-luadns          Obtain certificates using a DNS TXT record (if you are
                        using LuaDNS for DNS). (default: False)
  --dns-nsone           Obtain certificates using a DNS TXT record (if you are
                        using NS1 for DNS). (default: False)
  --dns-ovh             Obtain certificates using a DNS TXT record (if you are
                        using OVH for DNS). (default: False)
  --dns-rfc2136         Obtain certificates using a DNS TXT record (if you are
                        using BIND for DNS). (default: False)
  --dns-route53         Obtain certificates using a DNS TXT record (if you are
                        using Route53 for DNS). (default: False)
  --dns-sakuracloud     Obtain certificates using a DNS TXT record (if you are
                        using Sakura Cloud for DNS). (default: False)

結構たくさんあります。

早速使ってみます。

今あるプラグインを確認。

$ certbot plugins

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* apache
Description: Apache Web Server plugin
Interfaces: IAuthenticator, IInstaller, IPlugin
Entry point: apache = certbot_apache.entrypoint:ENTRYPOINT

* nginx
Description: Nginx Web Server plugin
Interfaces: IAuthenticator, IInstaller, IPlugin
Entry point: nginx = certbot_nginx.configurator:NginxConfigurator

* standalone
Description: Spin up a temporary webserver
Interfaces: IAuthenticator, IPlugin
Entry point: standalone = certbot.plugins.standalone:Authenticator

* webroot
Description: Place files in webroot directory
Interfaces: IAuthenticator, IPlugin
Entry point: webroot = certbot.plugins.webroot:Authenticator
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

$ sudo certbot certonly --dns-google -d hoge.grasys.tech
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Could not choose appropriate plugin: The requested dns-google plugin does not appear to be installed
The requested dns-google plugin does not appear to be installed

プラグインは別途インストールが必要でした（そりゃ一覧にないからな）。入れましょう。

certbot コマンドではできないようなので、 yum で。

sudo yum install python-certbot-google-dns

yum じゃない場合は

pip install certbot-dns-google

とか。

一覧を再度確認します。

$ certbot plugins

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
* dns-google
Description: Obtain certificates using a DNS TXT record (if you are using Google
Cloud DNS for DNS).
Interfaces: IAuthenticator, IPlugin
Entry point: dns-google = certbot_dns_google.dns_google:Authenticator

* standalone
Description: Spin up a temporary webserver
Interfaces: IAuthenticator, IPlugin
Entry point: standalone = certbot.plugins.standalone:Authenticator

* webroot
Description: Place files in webroot directory
Interfaces: IAuthenticator, IPlugin
Entry point: webroot = certbot.plugins.webroot:Authenticator
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

apache とか nginx のが消えたのですがががが・・・

使わないので先に進みましょう

まずはヘルプを読みます。

$ certbot --help dns-google
usage:
  certbot [SUBCOMMAND] [options] [-d DOMAIN] [-d DOMAIN] ...

Certbot can obtain and install HTTPS/TLS/SSL certificates.  By default,
it will attempt to use a webserver both for obtaining and installing the
certificate.

optional arguments:
  -h, --help            show this help message and exit
  -c CONFIG_FILE, --config CONFIG_FILE
                        path to config file (default: /etc/letsencrypt/cli.ini
                        and ~/.config/letsencrypt/cli.ini)

dns-google:
  Obtain certificates using a DNS TXT record (if you are using Google Cloud (GCP)
  DNS for DNS).

  --dns-google-propagation-seconds DNS_GOOGLE_PROPAGATION_SECONDS
                        The number of seconds to wait for DNS to propagate
                        before asking the ACME server to verify the DNS
                        record. (default: 60)
  --dns-google-credentials DNS_GOOGLE_CREDENTIALS
                        Path to Google Cloud (GCP) DNS service account JSON file.
                        (See https://developers.google.com/identity/protocols/
                        OAuth2ServiceAccount#creatinganaccount forinformation
                        about creating a service account and
                        https://cloud.google.com/dns/access-
                        control#permissions_and_roles for information about
                        therequired permissions.) (default: None)

GCE上などで実行するか、別途 Google Cloud (GCP) DNS を操作可能なサービスアカウントの JSON ファイルを用意しておく必要があります。

今回は GCE上で実行します。ローカルのMacからやろうとしたら、MetaDataが取れないせいか gcloud auth login していても --dns-google-credentials しないとダメでした。

やってみる

$ sudo certbot certonly --dns-google -d hoge.grasys.tech
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator dns-google, Installer None
Enter email address (used for urgent renewal and security notices) (Enter 'c' to
cancel): YOUR@MAILADDRESS
Starting new HTTPS connection (1): acme-v02.api.letsencrypt.org

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Please read the Terms of Service at
https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf. You must
agree in order to register with the ACME server at
https://acme-v02.api.letsencrypt.org/directoryß
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(A)gree/(C)ancel: A

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Would you be willing to share your email address with the Electronic Frontier
Foundation, a founding partner of the Let's Encrypt project and the non-profit
organization that develops Certbot? We'd like to send you email about our work
encrypting the web, EFF news, campaigns, and ways to support digital freedom.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(Y)es/(N)o: N
Obtaining a new certificate
Performing the following challenges:
dns-01 challenge for hoge.grasys.tech
URL being requested: GET https://www.googleapis.com/discovery/v1/apis/dns/v1/rest
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones?alt=json&dnsName=hoge.grasys.tech.
Attempting refresh to obtain initial access_token
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones?alt=json&dnsName=grasys.tech.
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones/XXXXXXXXXXXXXXXXXX/rrsets?alt=json
URL being requested: POST https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones/XXXXXXXXXXXXXXXXXX/changes?alt=json
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones/XXXXXXXXXXXXXXXXXX/changes/255?alt=json
Waiting 60 seconds for DNS changes to propagate
Waiting for verification...
Cleaning up challenges
URL being requested: GET https://www.googleapis.com/discovery/v1/apis/dns/v1/rest
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones?alt=json&dnsName=hoge.grasys.tech.
Attempting refresh to obtain initial access_token
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones?alt=json&dnsName=grasys.tech.
URL being requested: GET https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones/XXXXXXXXXXXXXXXXXX/rrsets?alt=json
URL being requested: POST https://dns.googleapis.com/dns/v1/projects/YOUR_PROJECT/managedZones/XXXXXXXXXXXXXXXXXX/changes?alt=json

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/hoge.grasys.tech/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/hoge.grasys.tech/privkey.pem
   Your cert will expire on 2019-11-20. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again. To non-interactively renew *all* of your certificates, run
   "certbot renew"
 - Your account credentials have been saved in your Certbot
   configuration directory at /etc/letsencrypt. You should make a
   secure backup of this folder now. This configuration directory will
   also contain certificates and private keys obtained by Certbot so
   making regular backups of this folder is ideal.
 - If you like Certbot, please consider supporting our work by:

   Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
   Donating to EFF:                    https://eff.org/donate-le

できました。手動で TXT レコード入れたりしないといけないのか？！？？？！！！とかなっていましたが、全て自動でやってくれました。

更新は certbot renew するだけでよさそうですが --dns-google-credentials つけて実行したドメインの設定ファイルを覗いてみたところ

/etc/letsencrypt/renewal/DOMAIN_NAME.conf

dns_google_credentials = PROJECT_NAME-0000000000000.json

ってなってたので、cron で renew 実行したい場合は、フルパスで指定しておいたほうが安心かもしれません。

AWS で EC2+Route53 でもためそうと思ったのですが、Route53 を使っているドメインが手元になかったので、そのうち。

それでは今回はこの辺で。

株式会社grasys(グラシス)は、技術が好きで一緒に夢中になれる仲間を募集しています。

grasysは、大規模・高負荷・高集積・高密度なシステムを多く扱っているITインフラの会社です。Google Cloud (GCP)、Amazon Web Services (AWS)、Microsoft Azureの最先端技術を活用してクラウドインフラやデータ分析基盤など、ITシステムの重要な基盤を設計・構築し、改善を続けながら運用しています。

お客様の課題解決をしながら技術を広げたい方、攻めのインフラ技術を習得したい方、とことん技術を追求したい方にとって素晴らしい環境が、grasysにはあります。
お気軽にご連絡ください。

noriko

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[Let’s Encrypt] DNS-01 challenge はいいぞ

certbot コマンドで DNS-01 challenge してみる

certbot プラグインの準備

やってみる

noriko

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