Certbot

Certbot is a free, open-source tool that automates the process of obtaining and renewing SSL/TLS certificates from Let’s Encrypt, a Certificate Authority (CA) that provides free certificates. SSL/TLS certificates are essential for enabling HTTPS, which encrypts data transmitted between your server and clients, ensuring security and privacy. Certbot makes it easy to secure websites by automating certificate issuance and renewal.

1. What is Certbot?

Certbot is a client application for Let’s Encrypt that helps users automatically obtain and install SSL/TLS certificates for their web servers. It simplifies the process of transitioning websites from HTTP to HTTPS by handling the creation, validation, issuance, and renewal of certificates.

Key Features:

Free Certificates: Certbot works with Let’s Encrypt, a free CA, to obtain free SSL/TLS certificates.
Automation: Certbot automates the process of obtaining and renewing certificates, ensuring that HTTPS is always enabled.
Integration with Web Servers: Certbot can automatically configure popular web servers (e.g., Apache, Nginx) to use SSL.
Cross-Platform: Certbot works on most Unix-based systems (e.g., Linux, macOS), as well as Windows.

2. How SSL/TLS Certificates Work

SSL/TLS certificates enable secure HTTPS connections by encrypting data exchanged between clients (e.g., browsers) and servers.

The process involves: - Public/Private Key Pair: A certificate is a public key associated with a domain name. The server holds the private key, and the client encrypts messages using the public key, ensuring only the server can decrypt them. - Certificate Validation: Certbot verifies the ownership of the domain for which the certificate is requested. - Certificate Expiry: Let’s Encrypt certificates are valid for 90 days. Certbot can be set to automatically renew them.

3. How Certbot Works

Certbot works through a challenge-response process where Let’s Encrypt validates that you control the domain for which you’re requesting the certificate. The most common validation method is HTTP-01 challenge.

HTTP-01 Challenge: Certbot temporarily creates a special file on your web server that Let’s Encrypt checks over HTTP. If Let’s Encrypt can access the file, the challenge is completed successfully, and the certificate is issued.
DNS-01 Challenge: For wildcard certificates or in some special configurations, Certbot may use a DNS challenge where it verifies ownership by checking a DNS TXT record.

Once Certbot obtains the certificate, it configures your web server to use it, ensuring a secure HTTPS connection.

4. Installation of Certbot

Certbot can be installed on most operating systems, and it integrates well with popular web servers such as Apache and Nginx.

a. Installation on Ubuntu/Debian (Nginx)

Add Certbot’s PPA (Personal Package Archive):

sudo apt update
sudo apt install software-properties-common
sudo add-apt-repository universe
sudo add-apt-repository ppa:certbot/certbot
sudo apt update

Install Certbot for Nginx:

sudo apt install certbot python3-certbot-nginx

b. Installation on CentOS/RHEL (Nginx)

Enable EPEL repository:
```
sudo yum install epel-release
```

Install Certbot for Nginx:

sudo yum install certbot python3-certbot-nginx

c. Installation on Windows

Certbot can also be installed on Windows through the official Certbot repository.

d. Docker Installation

Certbot can be run as a Docker container:

docker run -it --rm --name certbot \
    -v "/etc/letsencrypt:/etc/letsencrypt" \
    -v "/var/lib/letsencrypt:/var/lib/letsencrypt" \
    certbot/certbot certonly --nginx

5. Obtaining and Installing SSL Certificates with Certbot

Once Certbot is installed, you can use it to obtain and install SSL certificates for your domain.

a. Nginx Auto-Configuration

Certbot can automatically obtain a certificate and configure Nginx for HTTPS:

Run the Certbot command for Nginx:
```
sudo certbot --nginx
```
Certbot will prompt you to enter your email, agree to the terms, and select the domain names for which you want to obtain certificates.
Certbot will automatically update your Nginx configuration to use the new certificates, and your site will be accessible via HTTPS.

b. Apache Auto-Configuration

If you’re using Apache, the process is similar:

Install Certbot for Apache:
```
sudo apt install python3-certbot-apache
```
Obtain and configure certificates:
```
sudo certbot --apache
```

c. Manual Mode

If you’re using a web server that Certbot doesn’t support for automatic configuration, or if you want to handle installation manually, you can use Certonly mode:

sudo certbot certonly --manual

Certbot will provide instructions on setting up the challenge (e.g., placing a file on your server or configuring DNS), and once validated, it will generate the certificate files in /etc/letsencrypt/live.

6. Auto-Renewal of Certificates

Let’s Encrypt certificates expire after 90 days, but Certbot can be configured to automatically renew them.

a. Automatic Renewal

Certbot installs a cron job or systemd timer that checks your certificates regularly and renews them if they’re nearing expiration. You can check whether the renewal service is active by running:

systemctl list-timers | grep certbot

b. Testing Auto-Renewal

You can simulate the renewal process to ensure it works:

sudo certbot renew --dry-run

If successful, Certbot will automatically renew certificates before they expire.

c. Manual Renewal

If you prefer to renew certificates manually, you can use the following command:

sudo certbot renew

7. Wildcard Certificates

Wildcard certificates allow you to secure multiple subdomains with a single certificate. For example, a wildcard certificate for *.example.com would cover www.example.com, api.example.com, etc.

Certbot supports obtaining wildcard certificates using the DNS-01 challenge, which requires adding a DNS TXT record to your domain’s DNS settings.

Obtaining a Wildcard Certificate:

Run Certbot in manual mode with the DNS challenge:

sudo certbot certonly --manual --preferred-challenges dns -d *.example.com -d example.com

Certbot will instruct you to create a TXT record in your DNS with a specified value. After adding the DNS record, Certbot will verify it and issue the wildcard certificate.

8. Certbot Commands Overview

Certbot offers various commands for obtaining, renewing, and managing certificates:

Obtain and Install Certificate (Nginx/Apache):

sudo certbot --nginx  # For Nginx
sudo certbot --apache  # For Apache

Obtain Certificate without Web Server Configuration:
```
sudo certbot certonly --manual
```
Renew All Certificates:
```
sudo certbot renew
```
Simulate Renewal for Testing:
```
sudo certbot renew --dry-run
```
List All Certificates:
```
sudo certbot certificates
```

Revoke a Certificate:

sudo certbot revoke --cert-path /etc/letsencrypt/live/example.com/fullchain.pem

Delete a Certificate:

sudo certbot delete --cert-name example.com

9. Certbot with DNS API for Automatic DNS-01 Challenge

For fully automating wildcard certificate issuance or using the DNS-01 challenge, Certbot integrates with DNS providers via their APIs. You’ll need credentials (API keys) for your DNS provider.

Here’s an example of how to use Certbot with the Cloudflare DNS API:

Install the Cloudflare plugin:

sudo apt install python3-certbot-dns-cloudflare

Use the DNS challenge with Cloudflare:

sudo certbot certonly \
  --dns-cloudflare \
  --dns-cloudflare-credentials /path/to/your/cloudflare.ini \
  -d example.com \
  -d *.example.com

10. Certbot Advanced Configuration

Certbot provides additional flexibility for different use cases:

a. Custom Webroot

You can specify a custom webroot directory to place the validation challenge file for HTTP-01 challenges:

sudo certbot certonly --webroot -w /var/www/html -d example.com

b. Using Hooks

Certbot allows you to run custom commands during certificate issuance or renewal using hooks. Hooks can be used to restart services or perform actions after a successful

renewal.

Pre-Hook: Runs before obtaining or renewing a certificate.
Post-Hook: Runs after the certificate is obtained.
Renew-Hook: Runs after every renewal.

Example of a renewal hook to reload Nginx:

sudo certbot renew --deploy-hook "systemctl reload nginx"

c. Staging Environment

You can use Certbot’s staging environment to test the issuance process without hitting Let’s Encrypt’s rate limits:

sudo certbot --staging --nginx

11. Managing Multiple Domains

Certbot allows you to manage certificates for multiple domains, even combining multiple domain names in a single certificate.

Issue a Multi-Domain Certificate:

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

This will issue a certificate that covers all specified domains.

12. Certbot for Other Web Servers

Although Certbot offers automated configuration for Nginx and Apache, you can use it with other web servers (e.g., Caddy, HAProxy, Lighttpd) by using certonly mode and manually configuring the certificate.

Example for HAProxy:

Obtain the certificate:

sudo certbot certonly --standalone -d example.com

Configure HAProxy to use the generated certificate:

bind *:443 ssl crt /etc/letsencrypt/live/example.com/fullchain.pem

13. Certbot Logging

Certbot logs its actions to /var/log/letsencrypt/. This directory contains detailed logs about every certificate issuance or renewal attempt, which can be helpful for debugging or reviewing the certificate process.

14. Rate Limits

Let’s Encrypt imposes rate limits to prevent abuse:

Certificates per Registered Domain: You can issue a maximum of 50 certificates per domain per week.
Duplicate Certificate Limit: 5 duplicate certificates for the same domain set per week.
Account Limits: Each account can create up to 300 new orders per 3 hours.

You can check Let’s Encrypt’s official rate limits documentation for detailed information: Let’s Encrypt Rate Limits.

15. Certbot Security Considerations

a. Private Key Security

The private key for your certificates is stored in /etc/letsencrypt/live/domain_name/privkey.pem. Ensure that this directory is accessible only to root and the necessary services to prevent unauthorized access.

b. Firewall Configuration

Ensure that your firewall allows incoming traffic on port 80 (for the HTTP-01 challenge) and port 443 for HTTPS.