build-hosts.clj

;; My IP address data is shaped like this:
(def data {"host-a"    {:ip "1.1.1.1"}
           "host-b"    {:ip "2.2.2.2"}
           "container" {"host-c" {:ip "3.3.3.3"}
                        "host-d" {:ip "4.4.4.4"}}})

;; This logic turns that data into a map ("set" in nix) that would work for `networking.hosts`:
(defn build-hosts [ip-data & [name-prefix]]
  (reduce-kv (fn [result hostname {:keys [ip] :as info}]
               (let [full-hostname (if name-prefix
                                     (str name-prefix "-" hostname)
                                     hostname)]
                 (if ip
                   (assoc result ip [full-hostname])
                   (merge result (build-hosts info hostname)))))
             {}
             ip-data))


(build-hosts data)
=> {"1.1.1.1" ["host-a"],
    "2.2.2.2" ["host-b"],
    "3.3.3.3" ["container-host-c"],
    "4.4.4.4" ["container-host-d"]}