ArcGIS Notebook Server supports multiple-machine sites at 10.7.1 and later versions. In a multiple-machine site, each machine is configured the same, with identical Docker setups, and each can run ArcGIS Notebooks.
If you have a few notebook users who require more machine resources, you might evaluate modifying your site's resource limits as a limited alternative to adding machines.
To set up a multiple-machine ArcGIS Notebook Server site, you must first create a new site from one machine. Then, you can join your additional machines to the site. All machines must have the ArcGIS Notebook Server software installed at the same version, using the same license file and Docker container images. You can expand an ArcGIS Notebook Server 10.7.1 site from one to multiple machines at any time.
When your notebook users reference portal items in their notebooks, all analysis and processing of those items uses the portal's hosting server. If there are many notebooks in your site, or many concurrent notebooks that reference portal items, and the hosting server site does not have adequate processing resources for them, notebook performance can decrease. When you expand your ArcGIS Notebook Server site from one to multiple machines, you should accordingly consider expanding the machine resources available in the ArcGIS Server site that's registered as the hosting server.
If you are upgrading a single-machine site from 10.7 to 10.7.1 and want to expand the site with additional machines, first upgrade the site, specify a shared location for the configuration store and for the server directory paths, and then follow the steps to join the additional machines to the site.
When you have multiple machines in a site, your server directories and configuration store must be on shared drives accessible to each machine.
Follow the steps in the ArcGIS Notebook Server installation guide to set up a multiple-machine site. The guide will indicate when additional steps are needed for multiple-machine sites.