Scale

• Scale-out is more cost efficient than scale-up
• Persist with filesystems only read-only data like logging and backups

• create on independent server for each core (CPU)
• don’t create more than one cluster per core otherwise the extra servers will be useless

• Maximize server performance (hardware or virtual machine)
• low overhead to test your app under parallel conditions

• when a script is run directly, will be true.
• if false, it means your script has been loaded from another script using require.
• virtual machines default to a single core.

Scaling Out with Multiple Servers

• To scale out you need a proxy server (often called a reverse proxy or forward-facing proxy.)
• Most popular: Nginx and HAProxy
• Dev proxies: and node-http-proxy

Working with proxies

• if you use a proxy server, make sure to tell Express to trust it with app.enable('trust proxy');
• this will ensure that , req.protocol, and reflect details about the connection client <> proxy, and not client<>server