IPv6 unique-local addresses suitable for internal networks Let's consider a webfarm where each server has two interfaces: one bound to an internal-only, physically separated, network and the other cabled to the switch with the uplink to the public Internet. This second interface is used only when it is necessary to expose the server on public network, and is not connected otherwise (for example, on a database server). What kind of IPv6 addresses should be used on this internal-only network, considered that "site-local" addresses are gone? Are "unique-local" addresses established enough so that they won't be deprecated like the "site-local" ones?

Yes, ULA (Unique Local Addresses) are the way to go. The site-local addresses were deprecated because every site would use the same addresses, which would cause conflicts when setting up VPNs or when e.g. merging companies. ULA was designed to solve this and replace site-local.