Let' EncryptでのSSL/TLS証明書申請の更新がうまく行かないとき

Djangoで作ったアプリケーションをnginx+gunicornでデプロイし、セキュア化するためのLet' EncryptでのSSL/TLS証明書申請をしましたが、原則的に90日間しか効力がありません。そのため、「再申請をしてくれ」との更新案内がメールに届きましたが、普通に使う「# certbot renew」がうまく行かず、一日中ハマりましたので、いろいろ試しましたが、うまく行きません。最終的に上手く行ったかに見えるサイト管理者（筆者）なりの対処策を備忘録として残しておきます。

さくらのVPSにデプロイしましたDjangoアプリケーションですが、結論は、再度申請をし直すことでした。

root@tk2-411-46749:~# certbot certonly --webroot -w /var/www/letsencrypt -d www2.it-ibfs.org
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Certificate not yet due for renewal

You have an existing certificate that has exactly the same domains or certificate name you requested and isn't close to expiry.
(ref: /etc/letsencrypt/renewal/www2.it-ibfs.org.conf)

What would you like to do?
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1: Keep the existing certificate for now
2: Renew & replace the certificate (may be subject to CA rate limits)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Select the appropriate number [1-2] then [enter] (press 'c' to cancel): 2
Renewing an existing certificate for www2.it-ibfs.org

Successfully received certificate.
Certificate is saved at: /etc/letsencrypt/live/www2.it-ibfs.org/fullchain.pem
Key is saved at: /etc/letsencrypt/live/www2.it-ibfs.org/privkey.pem
This certificate expires on 2023-07-06.
These files will be updated when the certificate renews.
Certbot has set up a scheduled task to automatically renew this certificate in the background.

なお、nginxの設定ファイル（/etc/nginx/sites-enabled/default）は次のようになっています。

  
# Virtual Host configuration for example.com
#
# You can move that to a different file under sites-available/ and symlink that
# to sites-enabled/ to enable it.
#
server {
    listen  443 ssl http2 ;
    listen  [::]:443 ssl http2 ;

    ssl_certificate "/etc/letsencrypt/live/www2.it-ibfs.org/fullchain.pem";
    ssl_certificate_key "/etc/letsencrypt/live/www2.it-ibfs.org/privkey.pem";
    ssl_session_cache shared:SSL:1m;
    ssl_session_timeout  10m;

    server_name www2.it-ibfs.org;

    access_log /var/log/nginx/photo_access.log;
    error_log /var/log/nginx/photo_error.log;                                                                                 

    location /static/ {
        alias /var/www/django/photoproject/static/;
    }

    location /media/ {
        alias /var/www/django/photoproject/media/;
    }

    location ^~/.well-known/acme-challenge {
        allow all;
        root /var/www/letsencrypt;
        # root /usr/share/nginx/html;
        default_type "text/plain";
        # try_files $url $url =404;
    }

    location / {
        # proxy_set_header Host $http_host;
        # proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        # proxy_redirect off;
        # proxy_set_header X-Forwarded-Proto $scheme
        include proxy_params;                                                                                                 
        proxy_pass http://unix:/run/gunicorn.sock;
    }
    
}

ただし、location ^~/.well-known/acme-challenge {}のところは上手く動作しません。