Nginx Reverse Proxy with SSL for Multiple Apps

sudo apt update
sudo apt install -y nginx
sudo systemctl enable nginx
sudo systemctl start nginx
sudo systemctl status nginx --no-pager

sudo ufw allow OpenSSH
sudo ufw allow 'Nginx Full'
sudo ufw enable
sudo ufw status

sudo tee /etc/nginx/conf.d/upstreams.conf >/dev/null <<'EOF'
upstream app_main {
    server 127.0.0.1:3000;
}

upstream app_api {
    server 127.0.0.1:4000;
}
EOF

sudo tee /etc/nginx/sites-available/example.conf >/dev/null <<'EOF'
server {
    listen 80;
    listen [::]:80;
    server_name app.example.com api.example.com;

    location / {
        return 301 https://$host$request_uri;
    }
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name app.example.com;

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

    location / {
        proxy_pass http://app_main;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name api.example.com;

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

    location / {
        proxy_pass http://app_api;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}
EOF

sudo ln -s /etc/nginx/sites-available/example.conf /etc/nginx/sites-enabled/example.conf
sudo nginx -t
sudo systemctl reload nginx

sudo apt install -y certbot python3-certbot-nginx
sudo certbot --nginx -d app.example.com -d api.example.com --redirect --agree-tos -m admin@example.com --no-eff-email

systemctl list-timers | grep certbot
sudo certbot renew --dry-run

sudo tee /etc/nginx/snippets/ssl-params.conf >/dev/null <<'EOF'
ssl_protocols TLSv1.2 TLSv1.3;
ssl_prefer_server_ciphers off;
ssl_session_timeout 1d;
ssl_session_cache shared:SSL:10m;
ssl_session_tickets off;
add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
EOF