Migrating away from Codchi

One of our main principles is not to lock the user into Codchi. Code machines consist of three parts:

1. Configuration (NixOS modules)
2. File system state
3. The Codchi driver

To migrate away from Codchi just use your existing code machine configuration (1), copy your files (2) and bring your own hardware driver / configuration (3). For development environments this could be a VM. This is how it works in practise:

1. Install NixOS in a virtual machine. The easiest way is to use a graphical ISO image. Use codchi as your user name.
2. Export your code machine with codchi tar <MACHINE_NAME> my-files.tar
3. Copy my-files.tar to the VM and extract it:

   cd /
   sudo su
   tar --no-overwrite-dir -xf /path/to/my-files.tar
   chmod 755 /
   

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4. Add the VM configuration to your code machine flake:

   sudo nano /etc/nixos/flake.nix
   

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   {
     inputs = {
       codchi_driver.url = "github:aformatik/codchi/master";
       "codchi-secrets".url = "github:aformatik/codchi?host=github.com";
     };
     outputs = inputs: {
       nixosConfigurations.nixos = inputs."codchi-secrets".inputs.nixpkgs.lib.nixosSystem {
         system = "x86_64-linux";
         modules = [
           { 
                _module.args.inputs.nixpkgs = inputs."codchi-secrets".inputs.nixpkgs; 
                codchi.driver.name = "none";
           }
           inputs.codchi_driver.nixosModules.default
           inputs."codchi-secrets".nixosModules.secrets
           ./configuration.nix # <<<<<<<<<<<<<<<<<<<<<<<<<<<<<< add this line
         ];
       };
     };
   }
   

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5. Now build your system:

   sudo nixos-rebuild switch
   

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codchi tar creates a flake that uses exactly the same modules as the code machine, which means your VM can stay up to date with your code machine when using remote modules. Also Codchi's [custom NixOS options](../3.config/99.Codchi specific NixOS Options.md) will continue to work (without the Codchi host integration, like the GPU). Your secrets and previous machine name are stored in /etc/codchi-env.