Configure SSL/TLS with Let's Encrypt on Nginx

# Ubuntu/Debian
sudo apt update
sudo apt install certbot python3-certbot-nginx

# Get certificate
sudo certbot --nginx -d example.com -d www.example.com

# /etc/nginx/conf.d/ssl-params.conf
# Shared SSL parameters for all sites

ssl_protocols TLSv1.2 TLSv1.3;
ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384;
ssl_prefer_server_ciphers off;

# SSL session caching
ssl_session_timeout 1d;
ssl_session_cache shared:SSL:10m;
ssl_session_tickets off;

# OCSP Stapling
ssl_stapling on;
ssl_stapling_verify on;
resolver 8.8.8.8 8.8.4.4 valid=300s;
resolver_timeout 5s;

# DH parameters (generate with: openssl dhparam -out /etc/nginx/dhparam.pem 2048)
ssl_dhparam /etc/nginx/dhparam.pem;

# /etc/nginx/sites-available/example.com
# HTTP -> HTTPS redirect
server {
    listen 80;
    listen [::]:80;
    server_name example.com www.example.com;
    return 301 https://$server_name$request_uri;
}

# HTTPS server
server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name example.com www.example.com;

    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    # Include shared SSL parameters
    include /etc/nginx/conf.d/ssl-params.conf;

    # HSTS (31536000 seconds = 1 year)
    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;

    # Security headers
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Frame-Options "DENY" always;
    add_header X-XSS-Protection "1; mode=block" always;
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;

    root /var/www/example.com;
    index index.html;

    location / {
        try_files $uri $uri/ =404;
    }
}

# Certbot sets up auto-renewal automatically
# Verify with:
sudo certbot renew --dry-run

# Check renewal timer
systemctl status certbot.timer

# Test Nginx config
sudo nginx -t

# Reload
sudo systemctl reload nginx

# Test SSL (should show A+ on ssllabs.com)
curl -I https://example.com