Secrets

Sometimes there is the need for user-specific variables and / or secrets, which should not be included inside the .nix files inside a git repository, but they're still needed for the development environment. An example is a GitHub / GitLab token which is used to automatically setup mail and username for Git's config.

With Codchi these secrets can be described via NixOS options. Lateron, when a user installs a machine with this config, Codchi will prompt him to enter the specific secret value. The value is then made available via environment variables inside the machine.

Here's an example:

# configuration.nix
{
  codchi.secrets.env.TEST = {
      description = ''
        This is an example secret. Please enter a random value!
      '';
  };
}

We define the secret TEST and provide a description. When we build this code machine, we'll be prompted for a value for TEST:

> codchi rebuild foo
...
? Please enter secret 'TEST' (Toggle input mask with <Ctrl+R>): My Secret Value
[This is an example secret. Please enter a random value!]
...

> codchi exec foo
[codchi@nixos:~]$ env | grep CODCHI
CODCHI_TEST=My Secret Value
...

We can also use this secret inside systemd services (which run automatically on machine startup). For this we have to source /etc/codchi-env on service startup:

# configuration.nix
{ 
  systemd.services.my-secret-service = {
    description = "My Service which reads Codchi's secrets";
    wantedBy = [ "multi-user.target" ];

    script = ''
      source /etc/codchi-env
      echo "Got secret CODCHI_TEST=$CODCHI_TEST from codchi"
    '';
  };
}

We can view the latest log lines of the service:

[codchi@nixos:~]$ sudo systemctl status my-secret-service.service
○ my-secret-service.service - My Service which reads codchi's secrets
     Loaded: loaded (/etc/systemd/system/my-secret-service.service; enabled; preset: enabled)
    Drop-In: /nix/store/rrvw6pahhcvvhgp7vqb6v3pps1c7dl6v-system-units/service.d
             └─zzz-lxc-service.conf
     Active: inactive (dead) since Tue 2024-07-09 09:38:52 UTC; 3min 13s ago
   Duration: 3ms
    Process: 173 ExecStart=/nix/store/hv0hsyi0vb8va1jfnc03py7nylh2528c-unit-script-my-secret-service-start/bin/my-secret-service-start (code=exited, status=0/SUCCESS)
   Main PID: 173 (code=exited, status=0/SUCCESS)
        CPU: 3ms

Jul 09 09:38:52 nixos systemd[1]: Started My Service which reads codchi's secrets.
Jul 09 09:38:52 nixos my-secret-service-start[173]: Got secret CODCHI_TEST=My Secret Value from codchi <------------------------------------------
Jul 09 09:38:52 nixos systemd[1]: my-secret-service.service: Deactivated successfully.

Refer to the NixOS Options Reference for more details.

Modifying secrets

For now there is no interface for modifying secrets after they've been set. But this can be done manually by editing the config file for the machine <MACHINE_NAME>:

• Windows: %APPDATA%\codchi\machine\<MACHINE_NAME>\config.json (%APPDATA% is most likely C:\Users\NAME\AppData\Roaming)
• Linux: $XDG_CONFIG_HOME/codchi/machine/<MACHINE_NAME>/config.json ($XDG_CONFIG_HOME is most likely ~/.config)