Is it possible to extend the Rancher web UI in a standard way (i.e. without having to fork the source tree)? I was hoping there was a way to add a visualization of some CRD resource instance by having an additional item on the left menu when you are looking at a cluster and when the item was selected maybe Rancher could create a windows and call another container (service) and render the visualization based on the HTLM/JS that is returned from the call? Any standard way to do something like this?

I'd made a note to myself of https://rancher-users.slack.com/archives/C3ASABBD1/p1652183650869309 to look into that later. @stocky-account-63046 pointed out link https://rancher.com/docs/rancher/v2.6/en/admin-settings/branding/#custom-navigation-links for that.

Rancher is adding support for this functionality in 2.7.x. https://github.com/rancher/rancher/issues/36972

The UI has implemented a plugin process to allow developers to extend features (additional products, custom routes, components to create/edit/list, etc). This is already in the code base with some basic documentation https://github.com/rancher/dashboard/blob/master/docs/developer/PLUGINS.md (it's worth running through that directory, we are in the process of making it available via a more organised docusaurus site). This however only currently works at build time. As Catherine mentioned in the 2.7.x timeframe we're working on a way to persist these plugins and load them at runtime. Once that's in we should be able to support your feature of custom components for CRD management.