confctl

confctl is a Nix deployment configuration management tool. It can be used to build and deploy NixOS and vpsAdminOS machines.

Features

• Stateless
• Per-machine nixpkgs (both modules and packages)
• Build generations for easy rollback
• Rotation of old generations
• Support for configuration interconnections (declare and access other machines' configurations)
• Query machine state, view changelogs and diffs
• Run health checks

Requirements

• Nix

Quick start

1. Either install confctl as a gem: gem install confctl

Or clone this repository:

git clone https://github.com/vpsfreecz/confctl

This guide assumes you have cloned the repository, because otherwise man will not find confctl's manual pages. If you install confctl using gem, you can ignore steps with shell.nix.

1. Create a new directory, where your confctl-managed configuration will be stored:

mkdir cluster-configuration

1. Prepare shell.nix in the new directory:
   • Create a shell.nix and import the same file from confctl: cd cluster-configuration cat > shell.nix <<EOF import ../confctl/shell.nix EOF

• Alternatively, you can symlink shell.nix from the confctl repository: cd cluster-configuration ln -s ../confctl/shell.nix shell.nix

1. Enter the nix-shell. This will make confctl available and install its dependencies into .gems/: nix-shell

From within the shell, you can access the manual and a list of configuration options:

man confctl
man confctl-options.nix

1. Initialize the configuration directory with confctl:

   confctl init
   

2. Add a new machine to be deployed:

   confctl add my-machine
   

You can now edit the machine's configuration in directory cluster/my-machine.

1. Update pre-configured software pins to fetch current nixpkgs:

   confctl swpins update
   

2. Build the machine

   confctl build my-machine
   

3. Deploy the machine

   confctl deploy my-machine
   

Example configuration

Example configuration, which can be used as a starting point, can be found in directory example/.

See also existing configurations:

• vpsfree-cz-configuration
• vpsadminos-org-configuration

Configuration directory structure

confctl configurations should adhere to the following structure:

cluster-configuration/      # Configuration root
├── cluster/                # Machine configurations
│   ├── <name>/             # Single machine, can be nested directories
│   │   ├── config.nix      # Standard NixOS system configuration
│   │   └── module.nix      # Config with machine metadata used by confctl
│   ├── cluster.nix         # confctl-generated list of machines
│   └── module-list.nix     # List of all machine modules (including those in cluster.nix)
├── configs/                # confctl and other user-defined configs
│   ├── confctl.nix         # Configuration for the confctl tool itself
│   └── swpins.nix          # User-defined software pin channels
├── data/                   # User-defined datasets available in machine configurations as confData
├── environments/           # Environment presets for various types of machines, optional
├── modules/                # User-defined modules
│   └── cluster/default.nix # User-defined extensions of `cluster.` options used in `<machine>/module.nix` files
├── scripts/                # User-defined scripts
├── swpins/                 # confctl-generated software pins configuration
└── shell.nix               # Nix expression for nix-shell

Software pins

Software pins in confctl allow you to use specific revisions of nixpkgs or any other software to build and deploy target machines. It doesn't matter what nixpkgs version the build machine uses, because each machine gets its own nixpkgs as configured by the software pin.

Software pins can be grouped in channels, which can then be used by all or selected machines in the configuration. Or, if needed, custom software pins can be configured on selected machines. See below for usage examples.

Software pin channels

Software pin channels are defined in file confctl/swpins.nix:

{ config, ... }:
{
  confctl.swpins.channels = {
    # Channel for NixOS unstable
    nixos-unstable = {  # channel name
      nixpkgs = {  # swpin name
        # git-rev fetches the contents of a git commit and adds information
        # about the current git revision
        type = "git-rev";

        git-rev = {  # swpin type-specific configuration
          # Repository URL
          url = "https://github.com/NixOS/nixpkgs";

          # Fetch git submodules or not
          fetchSubmodules = false;

          # git reference to use for manual/automated update using
      # `confctl swpins channel update`
          update.ref = "refs/heads/nixos-unstable";

          # Whether to enable automated updates triggered by `confctl build | deploy`
          update.auto = true;

          # If update.auto is true, this determines how frequently will confctl
          # try to update the channel, in seconds
          update.interval = 60*60;
    };
      };
    };

    # Channel for vpsAdminOS staging
    vpsadminos-staging = {
      vpsadminos = {
        type = "git-rev";

        git-rev = {
          url = "https://github.com/vpsfreecz/vpsadminos";
          update.ref = "refs/heads/staging";
      update.auto = true;
        };
      };
    };
  };
}

This configuration defines what channels exist, what packages they contain and how to fetch them. Such configured channels can then be manipulated using confctl. confctl prefetches selected software pins and saves their hashes in JSON files in the swpins/ directory.

# List channels
$ confctl swpins channel ls
CHANNEL             SW           TYPE      PIN
nixos-unstable      nixpkgs      git-rev   1f77a4c8
vpsadminos-staging  vpsadminos   git-rev   9c9a7bcb

# Update channels with update.auto = true to reference in update.ref
$ confctl swpins channel update

# You can update only selected channels or swpins
$ confctl swpins channel update nixos-unstable
$ confctl swpins channel update nixos-unstable nixpkgs

# Set swpin to a custom git reference
$ confctl swpins channel set nixos-unstable nixpkgs 1f77a4c8

confctl build and confctl deploy will now use the prefetched software pins.

Machine metadata and software pins

Machine configuration directory usually contains at least two files: cluster/<machine name>/config.nix and cluster/<machine name>/module.nix.

config.nix is evaluated only when that particular machine is being built. It is a standard NixOS configuration module, similar to /etc/nixos/configuration.nix.

module.nix is specific to confctl configurations. module.nix files from all machines are evaluated during every build, whether that particular machine is being built or not. module.nix contains metadata about machines from which confctl knows how to treat them. It is also used to declare which software pins or channels the machine uses. Metadata about any machine can be read from config.nix of any other machine.

For example, machine named my-machine would be described in cluster/my-machine/module.nix as:

{ config, ... }:
{
  cluster."my-machine" = {
    # This tells confctl whether it is a NixOS or vpsAdminOS machine
    spin = "nixos";

    # Use NixOS unstable channel defined in configs/swpins.nix
    swpins.channels = [ "nixos-unstable" ];

    # If the machine name is not a hostname, configure the address to which
    # should confctl deploy it
    host.target = "<ip address>";
  };
}

See man/man8/confctl-options.nix.8.md for a list of all options.

Per-machine software pins

It is simpler to use software pins from channels, because they are usually used by multiple machines, but it is possible to define per-machine software pins, either to override pins from channels or add custom ones.

Per-machine software pins are configured in the machine's module.nix file:

{ config, ... }:
{
  cluster."my-machine" = {
    # List of channels
    swpins.channels = [ "..." ];

    # Per-machine swpins
    swpins.pins = {
      "pin-name" = {
          type = "git-rev";
      git-rev = {
            # ...pin definition...
      };
       };
    };
  };
}

The configuration is exactly the same as that of software pins in channels. Instead of confctl swpins channel commands, use confctl swpins cluster to manage configured pins.

Nix flakes

confctl's software pins are an alternative to flakes and flakes are not supported by confctl at this time. Software pins are implemented by manipulating the $NIX_PATH environment variable, which is in conflict with using flakes. confctl is likely to be migrated to flakes when the interface will be stabilized. Since the transition is going to require a significant effort, there are no plans for it currently.

Extra module arguments

Machine configs can use the following extra module arguments:

• confDir - path to the cluster configuration directory
• confLib - confctl functions, see nix/lib/default.nix
• confData - access to user-defined datasets found in data/default.nix, see example/data/default.nix
• confMachine - attrset with information about the machine that is currently being built, contains key name and all options from machine metadata module
• swpins - attrset of software pins of the machine that is currently being built

For example in cluster/my-machine/config.nix:

{ config, lib, pkgs, confLib, confData, confMachine, ... }:
{
  # Set the hostname to the machine name from confctl
  networking.hostName = confMachine.name;

  # When used with the data defined at example/data/default.nix
  users.users.root.openssh.authorizedKeys.keys = with confData.sshKeys; admins;
}

confctl configuration

The confctl utility itself can be configured using configs/confctl.nix:

{ config, ... }:
{
  confctl = {
    # Columns that are shown by `confctl ls`. Any option from machine metadata
    # can be used.
    listColumns = {
      "name"
      "spin"
      "host.fqdn"
    };
  };
}

Health checks

Health checks can be used to verify that the deployed systems behave correctly, all services are running, etc. Health checks are run automatically after deploy and can also be run on demand using confctl health-check. Health checks are configured in machine metadata module, i.e. in cluster/<machine>/module.nix files.

{ config, ... }:
{
  cluster."my-machine" = {
    # [...]

    healthChecks = {
      # Check that there are no failed units (this is actually done automatically
      # by confctl, you don't need to do this yourself)
      systemd.systemProperties = [
        { property = "SystemState"; value = "running"; }
      ];

      # Check that the firewall is active, we can check any property of any service
      systemd.unitProperties."firewall.service" = [
        { property = "ActiveState"; value = "active"; }
      ];

      # Run arbitrary commands from the builder
      builderCommands = [
        # Ping the deployed machine
        { command = [ "ping" "-c1" "{host.fqdn}" ]; }
      ];

      # Run commands on the deployed machine
      machineCommands = [
        # Try to access a fictional internal web server
        { command = [ "curl" "-s" "http://localhost:80" ]; }

        # We can also check command output
        { command = [ "hostname" ]; standardOutput.match = "my-machine\n"; }
      ];
    };
  };
}

Rotate build generations

confctl can be used to rotate old generations both on the build machine and on the deployed machines.

Default rotation settings can be set in confctl settings at configs/confctl.nix:

{ config, lib, ... }:
with lib;
{
  confctl = {
    # Generations on the build machine
    buildGenerations = {
      # Keep at least 4 generations
      min = mkDefault 4;

      # Do not keep more than 10 generations
      max = mkDefault 10;

      # Delete generations older than 90 days
      maxAge = mkDefault (90*24*60*60);
    };

    # The same settings can be configured for generations on the deployed machines
    hostGenerations = {
      min = mkDefault 40;
      max = mkDefault 100;
      maxAge = mkDefault (180*24*60*60);

      # On the deployed machines, confctl can also run nix-collect-garbage to
      # delete unreachable store paths
      collectGarbage = mkDefault true;
    };
  };
}

If these settings are not set, confctl uses its own defaults. Further, rotation settings can be configured on per-machine basis in machine metadata module at cluster/<machine>/module.nix:

{ config, ... }:
{
  cluster."my-machine" = {
    # [...]

    buildGenerations = {
      min = 8;
      max = 16;
    };

    hostGenerations = {
      min = 80;
    };
  };
}

Settings from the machine metadata modules override default confctl settings from configs/confctl.nix.

To rotate the generations both on the build and deployed machines, run:

confctl generation rotate --local --remote

Generations can also be deleted manually, e.g. to delete generations older than 90 days, run:

confctl generation rm --local --remote '*' 30d

Extending machine metadata

To define your own options to be used within the cluster.<name> modules in cluster/<machine>/module.nix files, create file modules/cluster/default.nix, e.g.:

{ config, lib, ... }:
with lib;
let
  myMachine =
    { config, ... }:
    {
      options = {
        myParameter = mkOption { ... };
      };
    };
in {
  options = {
    cluster = mkOption {
      type = types.attrsOf (types.submodule myMachine);
    };
  };
}

Then you can use it in machine module as:

{ config, ... }:
{
  cluster."my-machine" = {
    myParameter = "1234";
  };
}

Note that these modules are self-contained. They are not evaluated with the full set of NixOS modules. You have to import modules that you need.

User-defined confctl commands

User-defined Ruby scripts can be placed in directory scripts. Each script should create a subclass of ConfCtl::UserScript and call class-method register. Scripts can define their own confctl subcommands.

Example user script

class MyScript < ConfCtl::UserScript
  register

  def setup_cli(app)
    app.desc 'My CLI command'
    app.command 'my-command' do |c|
      c.action &ConfCtl::Cli::Command.run(c, MyCommand, :run)
    end
  end
end

class MyCommand < ConfCtl::Cli::Command
  def run
    puts 'Hello world'
  end
end

More information

See the man pages for more information:

• confctl(8)
• confctl-options.nix(8)