When you have to scale horizontally(add more servers) - you will have to use load balancer. Load balancer can distribute traffic based on different algorithms like round robin, connections, resource usage, etc.

Before you scale horizontally - its better to try out scaling vertically (increase the hardware of the current server).

Nginx will surprise with its performance on how much it can deliver given enough hardware. Only problem with nginx is understanding the configuration part of nginx(sometimes it becomes tricky). There are some tools out there which can help - NGINXConfig | DigitalOcean .

As with any production configuration - you have to be sure of what your are doing. “When in doubt - research more”. Try out your changes on a dev server or staging server.