Authoring a clanModule

This site will guide you through authoring your first module. Explaining which conventions must be followed, such that others will have an enjoyable experience and the module can be used with minimal effort.

:fontawesome-solid-road-barrier: :fontawesome-solid-road-barrier: :fontawesome-solid-road-barrier: Under construction :fontawesome-solid-road-barrier: :fontawesome-solid-road-barrier: :fontawesome-solid-road-barrier:

!!! Tip External ClanModules can be ad-hoc loaded via clan.inventory.modules

Bootstrapping the `clanModule`

A ClanModule is a specific subset of a NixOS Module, but it has some constraints and might be used via the Inventory interface. In fact a ClanModule can be thought of as a layer of abstraction on-top of NixOS and/or other ClanModules. It may configure sane defaults and provide an ergonomic interface that is easy to use and can also be used via a UI that is under development currently.

Because ClanModules should be configurable via json/API all of its interface (options) must be serializable.

!!! Tip ClanModules interface can be checked by running the json schema converter as follows.

`nix build .#legacyPackages.x86_64-linux.schemas.inventory`

If the build succeeds the module is compatible.

Directory structure

Each module SHOULD be a directory of the following format:

# Example: borgbackup
clanModules/borgbackup
├── README.md
└── roles
    ├── client.nix
    └── server.nix

!!! Tip README.md is always required. See section Readme for further details.

The `roles` folder is strictly required for `features = [ "inventory" ]`.

=== "User module"

If the module should be ad-hoc loaded.
It can be made avilable in any project via the [`clan.inventory.modules`](../reference/nix-api/inventory.md#modules) attribute.

```nix title="flake.nix"
# ...
buildClan {
    # 1. Add the module to the avilable inventory modules
    inventory.modules = {
        custom-module = ./modules/my_module;
    };
    # 2. Use the module in the inventory
    inventory.services = {
        custom-module.instance_1 = {
            roles.default.machines = [ "machineA" ];
        };
    };
};
```

=== "Upstream module"

If the module will be contributed to [`clan-core`](https://git.clan.lol/clan-core)
The clanModule must be registered within the `clanModules` attribute in `clan-core`

```nix title="clanModules/flake-module.nix"
--8<-- "clanModules/flake-module.nix:0:5"
    # Register our new module here
    # ...
```

Readme

The README.md is a required file for all modules. It MUST contain frontmatter in toml format.

---
description = "Module A"
---

This is the example module that does xyz.

See the Full Frontmatter reference further details and all supported attributes.

Roles

If the module declares to implement features = [ "inventory" ] then it MUST contain a roles directory.

Each .nix file in the roles directory is added as a role to the inventory service.

Other files can also be placed alongside the .nix files

└── roles
    ├── client.nix
    └── server.nix

Adds the roles: client and server

??? Tip "Good to know" Sometimes a ClanModule should be usable via both clan's inventory concept but also natively as a NixOS module.

> In the long term, we want most modules to implement support for the inventory,
> but we are also aware that there are certain low-level modules that always serve as a backend for other higher-level inventory modules.
> These modules may not want to implement inventory interfaces as they are always used directly by other modules.

This can be achieved by placing an additional `default.nix` into the root of the ClanModules directory as shown:

```sh
# ModuleA
├── README.md
├── default.nix
└── roles
    └── default.nix
```

```nix title="default.nix"
{...}:{
    imports = [ ./roles/default.nix ];
}
```

By utilizing this pattern the module (`moduleA`) can then be imported into any regular NixOS module via:

```nix
{...}:{
    imports  = [ clanModules.moduleA ];
}
```

Organizing the ClanModule

Each {role}.nix is included into the machine if the machine is declared to have the role.

For example

roles.client.machines = ["MachineA"];

Then roles/client.nix will be added to the machine MachineA.

This behavior makes it possible to split the interface and common code paths when using multiple roles. In the concrete example of borgbackup this allows a server to declare a different interface than the corresponding client.

The client offers configuration option, to exclude certain local directories from being backed up:

# Example client interface
  options.clan.borgbackup.exclude = ...

The server doesn't offer any configuration option. Because everything is set-up automatically.

# Example server interface
  options.clan.borgbackup = {};

Assuming that there is a common code path or a common interface between server and client this can be structured as:

{...}: {
    # ...
    imports = [ ../common.nix ];
}

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