Scalable WordPress hosting is a feature that Nexcess offers on its Managed WordPress and Managed WooCommerce plans. Nexcess provides cloud auto scaling which will automatically add extra PHP workers for your site when the sites PHP worker usage goes over those that are provided with your plan.
Cloud auto scaling is like having extra horsepower for more site processes when you need them. You can find out more about cloud auto scaling in this help article.
Nexcess also offers advanced auto scaling on Managed WordPress and Managed WooCommerce plans. The reason why would want to use the advanced auto scaling feature would be when your site is under a very high concurrent load.
Advanced auto scaling uses containers for the extra PHP workers for your site. In order to be able to use advanced auto scaling for your site, you will need to disabled the cloud auto scaling and then enabled advanced auto scaling in the portal of your site. Each container would be used for the extra 10 PHP workers. You can add additional containers for extra PHP workers if needed.
Another way to help your site be scalable is to use a full page cache plugin on your site, along with Redis object caching. You can use full page caching, Redis object caching with a site CDN which will help your site serve out site assets to users on your site.
Full page caching, Redis object caching, using a CDN, along with auto scaling will help your site scale and be able to deal with an increase in traffic and be able to cope with a higher demand on your site.