有効期限の確認

[root@example ~]# certbot certificates
Saving debug log to /var/log/letsencrypt/letsencrypt.log

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Found the following certs:
  Certificate Name: example
    Serial Number: 49f082d83bf7403eed28e28a64879b024cb
    Key Type: RSA
    Domains: example
    Expiry Date: 2021-10-20 10:26:46+00:00 (VALID: 89 days)
    Certificate Path: /etc/letsencrypt/live/example/fullchain.pem
    Private Key Path: /etc/letsencrypt/live/example/privkey.pem
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[root@example ~]#

Expiry Date: 2021-10-20 10:26:46+00:00 (VALID: 89 days)

↑の箇所に有効期限がでる

更新できるかテスト

certbot renew +--dry-run
更新コマンドとオプションを付けて実行、実際には更新されない

[root@example ~]# certbot renew --dry-run

Saving debug log to /var/log/letsencrypt/letsencrypt.log

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Processing /etc/letsencrypt/renewal/example.conf
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Cert not due for renewal, but simulating renewal for dry run
Plugins selected: Authenticator webroot, Installer None
Starting new HTTPS connection (1): acme-staging-v02.api.letsencrypt.org
Account registered.
Simulating renewal of an existing certificate for example
Performing the following challenges:
http-01 challenge for example
Using the webroot path /var/www/html for all unmatched domains.
Waiting for verification...
Cleaning up challenges

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new certificate deployed without reload, fullchain is
/etc/letsencrypt/live/example/fullchain.pem
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Congratulations, all simulated renewals succeeded:
  /etc/letsencrypt/live/example/fullchain.pem (success)
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[root@example ~]#

Congratulations, all renewals succeeded

こちらのメッセージが出ていれば
certbotでletsencryptが更新できる状態

optionを付けてのテスト1

--force-renew
更新期限に関係なく強制的に更新

[root@example ~]#certbot renew --force-renew --dry-run --webroot-path /var/www/html --post-hook "systemctl reload nginx"

略
Congratulations, all simulated renewals succeeded:
  /etc/letsencrypt/live/example/fullchain.pem (success)

が表示されて、テスト実行成功

optionを付けてのテスト2

--deploy-hook
実際には更新した時のみnginxを再起動したい
--dry-runのオプションを付けている段階では
エラーとして飛ばされる

[root@example ~] certbot renew --force-renew --dry-run --webroot-path /var/www/html --deploy-hook "systemctl reload nginx" >> /var/log/letsencrypt.log

略
Congratulations, all simulated renewals succeeded:
  /etc/letsencrypt/live/example/fullchain.pem (success)

cronが起動しているか確認

[root@example ~]# service crond status

Active: active (running)で起動している

cronの設定

/etc/cron.d配下にletsencryptファイルを作成し、
下記コマンドを記述（テスト実行の--dry-runを付けない）

毎月29日4:00に実行の設定の場合

00 4 29 * * certbot renew --force-renew --webroot-path /var/www/html --deploy-hook "systemctl reload nginx" >> /var/log/letsencrypt.log

[分] [時] [日] [月] [曜日] [コマンド]

毎月29日4:00にletsencrypt証明書を更新する
certbotが証明書更新の処理を終わった後のみnginxを再起動する。
/var/log/letsencrypt.logにlogを追記する

参考
https://qiita.com/katsukii/items/d5f90a6e4592d1414f99
https://qiita.com/tmatsumot/items/aca49d99558d2646ef36#letsencrypt%E3%81%A3%E3%81%A6