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Introduction

Let's Encrypt是一个证书颁发机构(CA),它提供了一种获取和安装免费TLS/SSL证书的可访问方式,从而在web服务器上启用加密HTTPS。它通过提供一个软件客户端Certbot来简化流程,该客户端尝试自动化大多数(如果不是全部的话)所需的步骤。目前,在Apache和Nginx上,获取和安装证书的整个过程都是完全自动化的。

在本教程中,您将使用Certbot在Ubuntu 22.04上获得Nginx的免费SSL证书,并设置证书自动续订。

本教程将使用一个单独的Nginx服务器配置文件,而不是默认文件。我们建议为每个域创建新的Nginx服务器块文件,因为这有助于避免常见错误,并将默认文件作为后备配置进行维护。

Prerequisites

To follow this tutorial, you will need:

  • One Ubuntu 22.04 server set up by following this initial server setup for Ubuntu 22.04 tutorial, including a sudo-enabled non-root user and a firewall.

  • A registered domain name. This tutorial will use example.com throughout. You can purchase a domain name from Namecheap, get one for free with Freenom, or use the domain registrar of your choice.

  • Both of the following DNS records set up for your server. If you are using DigitalOcean, please see our DNS documentation for details on how to add them.

    • An A record with example.com pointing to your server’s public IP address.
    • An A record with www.example.com pointing to your server’s public IP address.
  • Nginx installed by following How To Install Nginx on Ubuntu 22.04. Be sure that you have a server block for your domain. This tutorial will use /etc/nginx/sites-available/example.com as an example.

Step 1 — Installing Certbot

Certbot recommends using their snap package for installation. Snap packages work on nearly all Linux distributions, but they require that you’ve installed snapd first in order to manage snap packages. Ubuntu 22.04 comes with support for snaps out of the box, so you can start by making sure your snapd core is up to date:

  1. sudo snap install core; sudo snap refresh core

If you’re working on a server that previously had an older version of certbot installed, you should remove it before going any further:

  1. sudo apt remove certbot

After that, you can install the certbot package:

  1. sudo snap install --classic certbot

Finally, you can link the certbot command from the snap install directory to your path, so you’ll be able to run it by just typing certbot. This isn’t necessary with all packages, but snaps tend to be less intrusive by default, so they don’t conflict with any other system packages by accident:

  1. sudo ln -s /snap/bin/certbot /usr/bin/certbot

Now that we have Certbot installed, let’s run it to get our certificate.

Step 2 — Confirming Nginx’s Configuration

Certbot needs to be able to find the correct server block in your Nginx configuration for it to be able to automatically configure SSL. Specifically, it does this by looking for a server_name directive that matches the domain you request a certificate for.

If you followed the server block set up step in the Nginx installation tutorial, you should have a server block for your domain at /etc/nginx/sites-available/example.com with the server_name directive already set appropriately.

To check, open the configuration file for your domain using nano or your favorite text editor:

  1. sudo nano /etc/nginx/sites-available/example.com

Find the existing server_name line. It should look like this:

/etc/nginx/sites-available/example.com

...
server_name example.com www.example.com;
...

If it does, exit your editor and move on to the next step.

If it doesn’t, update it to match. Then save the file, quit your editor, and verify the syntax of your configuration edits:

  1. sudo nginx -t

If you get an error, reopen the server block file and check for any typos or missing characters. Once your configuration file’s syntax is correct, reload Nginx to load the new configuration:

  1. sudo systemctl reload nginx

Certbot can now find the correct server block and update it automatically.

Next, let’s update the firewall to allow HTTPS traffic.

Step 3 — Allowing HTTPS Through the Firewall

If you have the ufw firewall enabled, as recommended by the prerequisite guides, you’ll need to adjust the settings to allow for HTTPS traffic. Luckily, Nginx registers a few profiles with ufw upon installation.

You can see the current setting by typing:

  1. sudo ufw status

It will probably look like this, meaning that only HTTP traffic is allowed to the web server:

Output

Status: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere Nginx HTTP ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6) Nginx HTTP (v6) ALLOW Anywhere (v6)

To additionally let in HTTPS traffic, allow the Nginx Full profile and delete the redundant Nginx HTTP profile allowance:

  1. sudo ufw allow 'Nginx Full'
  2. sudo ufw delete allow 'Nginx HTTP'

Your status should now look like this:

  1. sudo ufw status

Output

Status: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere Nginx Full ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6) Nginx Full (v6) ALLOW Anywhere (v6)

Next, let’s run Certbot and fetch our certificates.

Step 4 — Obtaining an SSL Certificate

Certbot provides a variety of ways to obtain SSL certificates through plugins. The Nginx plugin will take care of reconfiguring Nginx and reloading the config whenever necessary. To use this plugin, type the following:

  1. sudo certbot --nginx -d example.com -d www.example.com

This runs certbot with the --nginx plugin, using -d to specify the domain names we’d like the certificate to be valid for.

When running the command, you will be prompted to enter an email address and agree to the terms of service. After doing so, you should see a message telling you the process was successful and where your certificates are stored:

Output

IMPORTANT NOTES: Successfully received certificate. Certificate is saved at: /etc/letsencrypt/live/your_domain/fullchain.pem Key is saved at: /etc/letsencrypt/live/your_domain/privkey.pem This certificate expires on 2022-06-01. These files will be updated when the certificate renews. Certbot has set up a scheduled task to automatically renew this certificate in the background. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 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

Your certificates are downloaded, installed, and loaded, and your Nginx configuration will now automatically redirect all web requests to https://. Try reloading your website and notice your browser’s security indicator. It should indicate that the site is properly secured, usually with a lock icon. If you test your server using the SSL Labs Server Test, it will get an A grade.

Let’s finish by testing the renewal process.

Step 5 — Verifying Certbot Auto-Renewal

Let’s Encrypt’s certificates are only valid for ninety days. This is to encourage users to automate their certificate renewal process. The certbot package we installed takes care of this for us by adding a systemd timer that will run twice a day and automatically renew any certificate that’s within thirty days of expiration.

You can query the status of the timer with systemctl:

  1. sudo systemctl status snap.certbot.renew.service

Output

○ snap.certbot.renew.service - Service for snap application certbot.renew Loaded: loaded (/etc/systemd/system/snap.certbot.renew.service; static) Active: inactive (dead) TriggeredBy: ● snap.certbot.renew.timer

To test the renewal process, you can do a dry run with certbot:

  1. sudo certbot renew --dry-run

如果你没有发现任何错误,你就做好了准备。必要时,Certbot将续订您的证书并重新加载Nginx以获取更改。如果自动续订过程失败,Let's Encrypt将向您指定的电子邮件发送一条消息,在证书即将过期时向您发出警告。

结论

在本教程中,您安装了Let's Encrypt客户端certbot,下载了域的SSL证书,将Nginx配置为使用这些证书,并设置了自动证书续订。如果您对使用Certbot有进一步的疑问,官方文档是一个很好的起点。