krops (krebs ops)

krops is a lightweigt toolkit to deploy NixOS systems, remotely or locally.

Some Features

store your secrets in password store
build your system remotely
minimal overhead (it's basically just nixos-rebuild switch!)
run from custom nixpkgs branch/checkout/fork

Minimal Example

Create a file named krops.nix (name doesn't matter) with following content:

let
  krops = (import <nixpkgs> {}).fetchgit {
    url = https://cgit.krebsco.de/krops/;
    rev = "v1.17.0";
    sha256 = "150jlz0hlb3ngf9a1c9xgcwzz1zz8v2lfgnzw08l3ajlaaai8smd";
  };

  lib = import "${krops}/lib";
  pkgs = import "${krops}/pkgs" {};

  source = lib.evalSource [{
    nixpkgs.git = {
      clean.exclude = ["/.version-suffix"];
      ref = "4b4bbce199d3b3a8001ee93495604289b01aaad3";
      url = https://github.com/NixOS/nixpkgs;
    };
    nixos-config.file = toString (pkgs.writeText "nixos-config" ''
      { pkgs, ... }: {
        fileSystems."/" = { device = "/dev/sda1"; };
        boot.loader.systemd-boot.enable = true;
        services.openssh.enable = true;
        environment.systemPackages = [ pkgs.git ];
        users.users.root.openssh.authorizedKeys.keys = [
          "ssh-rsa ADD_YOUR_OWN_PUBLIC_KEY_HERE user@localhost"
        ];
      }
    '');
  }];
in
  pkgs.krops.writeDeploy "deploy" {
    source = source;
    target = "root@YOUR_IP_ADDRESS_OR_HOST_NAME_HERE";
  }

and run $(nix-build --no-out-link krops.nix) to deploy the target machine.

Under the hood, this will make the sources available on the target machine below /var/src, and execute nixos-rebuild switch -I /var/src.

Deployment Target Attribute

The target attribute to writeDeploy can either be a string or an attribute set, specifying where to make the sources available, as well as where to run the deployment.

If specified as string, the format could be described as:

[[USER]@]HOST[:PORT][/SOME/PATH]

Portions in square brakets are optional.

If the USER is the empty string, as in e.g. @somehost, then the username will be obtained by SSH from its configuration files.

If the target attribute is an attribute set, then it has to define the attributes host, path, port, sudo, and user. This allows to deploy to targets that don't allow sshing in as root, but allow (preferably passwordless) sudo:

pkgs.krops.writeDeploy "deploy" {
  source = /* ... */;
  target = lib.mkTarget "user@host/path" // {
    sudo = true;
  };
}

For more details about the target attribute, please check the mkTarget function in lib/default.nix.

Source Types

`derivation`

Nix expression to be built at the target machine.

Supported attributes:

text - Nix expression to be built.

`file`

The file source type transfers local files (and folders) to the target using rsync.

Supported attributes:

path - absolute path to files that should by transfered
useChecksum (optional) - boolean that controls whether file contents should be checked to decide whether a file has changed. This is useful when path points at files with mangled timestamps, e.g. the Nix store.

`git`

Git sources that will be fetched on the target machine.

Supported attributes:

url - URL of the Git repository that should be fetched.
ref - Branch / tag / commit that should be fetched.
clean.exclude - List of patterns that should be excluded from Git cleaning.

`pass`

The pass source type transfers contents from a local password store to the target machine.

Supported attributes:

dir - absolute path to the password store.
name - sub-directory in the password store.

`pipe`

Executes a local command, capture its stdout, and send that as a file to the target machine.

Supported attributes:

command - The (shell) command to run.

`symlink`

Symlink to create at the target, relative to the target directory. This can be used to reference files in other sources.

Supported attributes:

target - Content of the symlink. This is typically a relative path.

References

In-depth example by Ingolf Wagner

Communication

Comments, questions, pull-requests, etc. are very welcome, and can be directed at:

IRC: #krebs at freenode
Mail: spam@krebsco.de