Setting Up Apache2 as a Reverse Proxy

Apache can act as a reverse proxy, forwarding requests to a backend application server (Node.js, a Python app, another internal service) while presenting a unified public-facing domain and handling SSL termination.

<VirtualHost *:443>
    ServerName app.example.com

    SSLEngine on
    SSLCertificateFile /etc/letsencrypt/live/app.example.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/app.example.com/privkey.pem

    ProxyPreserveHost On
    ProxyPass / http://127.0.0.1:3000/
    ProxyPassReverse / http://127.0.0.1:3000/

    # Needed for WebSocket support (e.g. a Node.js app using Socket.IO)
    RewriteEngine On
    RewriteCond %{HTTP:Upgrade} =websocket [NC]
    RewriteRule /(.*) ws://127.0.0.1:3000/$1 [P,L]
</VirtualHost>

sudo a2enmod proxy proxy_http proxy_wstunnel rewrite
sudo systemctl restart apache2

ProxyPreserveHost On matters more than it looks — without it, the backend application sees Apache’s internal hostname instead of the real public domain, which breaks anything relying on the Host header (redirects, generated URLs, some auth logic).

Setting Up Apache2 as a Reverse Proxy

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