Merge pull request 'machine/host: degrade into info and add docs' (#4238) from host-info into main

Reviewed-on: https://git.clan.lol/clan/clan-core/pulls/4238
Reviewed-by: Luis Hebendanz <consulting@qube.email>

docs/mkdocs.yml

@@ -62,6 +62,7 @@ nav:
       - Vars Backend: guides/vars-backend.md
       - Facts Backend: guides/secrets.md
       - Adding more machines: guides/more-machines.md
+      - Target Host: guides/target-host.md
       - Inventory:
           - Inventory: guides/inventory.md
       - Secure Boot: guides/secure-boot.md

docs/site/guides/target-host.md

@@ -0,0 +1,82 @@
+# How to Set `targetHost` for a Machine
+
+The `targetHost` defines where the machine can be reached for operations like SSH or deployment. You can set it in two ways, depending on your use case.
+
+---
+
+## ✅ Option 1: Use the Inventory (Recommended for Static Hosts)
+
+If the hostname is **static**, like `server.example.com`, set it in the **inventory**:
+
+```{.nix title="flake.nix" hl_lines="8"}
+{
+  # edlided
+  outputs =
+    { self, clan-core, ... }:
+    let
+      clan = clan-core.lib.clan {
+        inventory.machines.jon = {
+            deploy.targetHost = "root@server.example.com";
+        };
+      };
+    in
+    {
+      inherit (clan.config) nixosConfigurations nixosModules clanInternals;
+      # elided
+    };
+}
+```
+
+This is fast, simple and explicit, and doesn’t require evaluating the NixOS config. We can also displayed it in the clan-cli or clan-app.
+
+---
+
+## ✅ Option 2: Use NixOS (Only for Dynamic Hosts)
+
+If your target host depends on a **dynamic expression** (like using the machine’s evaluated FQDN), set it inside the NixOS module:
+
+```{.nix title="flake.nix" hl_lines="8"}
+{
+  # edlided
+  outputs =
+    { self, clan-core, ... }:
+    let
+      clan = clan-core.lib.clan {
+        machines.jon = {config, ...}: {
+            clan.core.networking.targetHost = "jon@${config.networking.fqdn}";
+        };
+      };
+    in
+    {
+      inherit (clan.config) nixosConfigurations nixosModules clanInternals;
+      # elided
+    };
+}
+```
+
+Use this **only if the value cannot be made static**, because it’s slower and won't be displayed in the clan-cli or clan-app yet.
+
+---
+
+## 📝 TL;DR
+
+| Use Case                  | Use Inventory? | Example                          |
+| ------------------------- | -------------- | -------------------------------- |
+| Static hostname           | ✅ Yes          | `root@server.example.com`        |
+| Dynamic config expression | ❌ No           | `jon@${config.networking.fqdn}` |
+
+---
+
+## 🚀 Coming Soon: Unified Networking Module
+
+We’re working on a new networking module that will automatically do all of this for you.
+
+- Easier to use
+- Sane defaults: You’ll always be able to reach the machine — no need to worry about hostnames.
+- ✨ Migration from **either method** will be supported and simple.
+
+## Summary
+
+- Ask: *Does this hostname dynamically change based on NixOS config?*
+- If **no**, use the inventory.
+- If **yes**, then use NixOS config.

pkgs/clan-cli/clan_lib/machines/machines.py

@@ -182,9 +182,10 @@ def get_machine_host(
     host_str = inv_machine.get("deploy", {}).get(field)
 
     if host_str is None:
-        machine.warn(
+        machine.info(
-            f"'{field}' is not set in `inventory.machines.${machine.name}.deploy.{field}` - falling back to _slower_ nixos option: `clan.core.networking.{field}`"
+            f"`inventory.machines.{machine.name}.deploy.{field}` is not set — falling back to `clan.core.networking.{field}`. See: https://docs.clan.lol/guides/target-host"
         )
+
         host_str = machine.select(f'config.clan.core.networking."{field}"')
         source = "machine"