blog: add third nix flakes post
Signed-off-by: Xe <me@christine.website>
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@ -136,7 +136,10 @@ Then you can look at `flake.nix` to see what's up:
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pkgs = nixpkgsFor.${system};
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in
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{
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go-hello = pkgs.buildGoModule {
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# The default package for 'nix build'. This makes sense if the
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# flake provides only one package or there is a clear "main"
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# package.
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default = pkgs.buildGoModule {
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pname = "go-hello";
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inherit version;
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# In 'nix develop', we don't need a copy of the source tree
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@ -156,11 +159,6 @@ Then you can look at `flake.nix` to see what's up:
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vendorSha256 = "sha256-pQpattmS9VmO3ZIQUFn66az8GSmB4IvYhTTCFn6SUmo=";
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};
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});
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# The default package for 'nix build'. This makes sense if the
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# flake provides only one package or there is a clear "main"
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# package.
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defaultPackage = forAllSystems (system: self.packages.${system}.go-hello);
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};
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}
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```
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@ -197,7 +195,6 @@ Let's take a closer look at the higher level things in the flake:
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outputs = { self, nixpkgs }: {
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packages = { ... };
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defaultPackage = { ... };
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};
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}
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```
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@ -462,7 +459,7 @@ nixosModules.bot = { config, lib, ... }: {
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Group = "mara-bot";
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Restart = "always";
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WorkingDirectory = "/var/lib/mara-bot";
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ExecStart = "${self.defaultPackage."${system}"}/bin/mara";
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ExecStart = "${self.packages."${system}".default}/bin/mara";
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};
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};
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};
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@ -19,6 +19,10 @@ chance of bitrotting. I will make every attempt to update it if things change,
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however flakes have been fairly consistent for a few years
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now.](conversation://Cadey/coffee)
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[EDIT(20220327 14:13): A previous version of this article said to use
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`defaultPackage` for the default package. This is deprecated and you should use
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`packages.default` instead.](conversation://Cadey/coffee)
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</div>
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[What is a package? I've seen this term thrown around with phrases like "Nix is a
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@ -180,10 +184,10 @@ web server template by defining another package:
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```nix
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# flake.nix
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# after defaultPackage
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packages = {
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default = ...;
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docker = let
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web = self.defaultPackage.${system};
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web = self.packages.${system}.default;
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in pkgs.dockerTools.buildLayeredImage {
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name = web.pname;
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tag = web.version;
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@ -373,7 +377,7 @@ the systemd unit:
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web-service = pkgs.substituteAll {
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name = "web-server.service";
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src = ./systemd/web-server.service.in;
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web = self.defaultPackage.${system};
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web = self.packages.${system}.default;
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};
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```
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@ -399,7 +403,7 @@ Then you can add the bit that builds the portable service:
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```nix
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portable = let
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web = self.defaultPackage.${system};
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web = self.packages.${system}.default;
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in pkgs.portableService {
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inherit (web) version;
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name = web.pname;
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@ -0,0 +1,364 @@
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---
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title: "Nix Flakes: Exposing and using NixOS Modules"
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date: 2022-03-31
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series: nix-flakes
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tags:
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- nixos
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vod:
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twitch: https://www.twitch.tv/videos/1437346416
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youtube: https://youtu.be/wCZ9SwmgSck
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---
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Nix flakes allow you to expose NixOS modules. NixOS modules are templates for
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system configuration and they are the basis of how you configure NixOS. Today
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we're going to take our Nix flake [from the last
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article](/blog/nix-flakes-2-2022-02-27) and write a NixOS module for it so that
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we can deploy it to a server.
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[If you haven't read <a href="/blog/series/nix-flakes">the other articles in
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this series</a>, you probably should. This article builds upon the previous
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ones.](conversation://Mara/hacker)
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NixOS modules are the main building block of how NixOS servers are configured.
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They are like lego blocks that help you build up a server from off the shelf
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parts. A module describes a desired system state and they build off of eachother
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in order to end up with a more elaborate result.
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[You can think about them like Ansible playbooks, but NixOS modules describe the
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desired end state instead of the steps you need to get to that end
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state.](conversation://Mara/hacker)
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NixOS modules are functions that take in the current state of the system and
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then return things to add to the state of the system. Here is a basic NixOS
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module that enables [nginx](https://nginx.org/):
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```nix
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{ config, pkgs, lib, ... }:
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{
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config = {
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services.nginx.enable = true;
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};
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}
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```
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This function takes in the state of the world and returns additions to the state
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of the world. This will use the nginx module that ships with NixOS to give you a
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basic nginx setup that has the upstream default configuration in it.
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NixOS has a way to run other instances of NixOS with [NixOS
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containers](https://nixos.org/manual/nixos/stable/index.html#ch-containers). We
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can use them to test our NixOS module as we write it.
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[This probably won't work on a non-NixOS machine. You will need to
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install NixOS in order to test this. For an easy way to do this, see <a
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href="https://github.com/elitak/nixos-infect">nixos-infect</a>, a script you can
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put into a cloudconfig when spinning up a new server. You can also <a
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href="https://nixos.org/manual/nixos/stable/index.html#sec-installation">install
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NixOS manually</a> in a VM, but for now it may be better to use a cloud server
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as the path of least resistance. Installing NixOS with a flake will be a part of
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a future article in this series.](conversation://Mara/hacker)
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In Nix you can merge two attribute sets using the `//` operator. This allows you
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to add two attribute sets into one larger one, such as like this:
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```
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nix-repl> { foo = 1; } // { bar = 2; }
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{ bar = 2; foo = 1; }
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```
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We will use this to add the container configuration to the flake at the end of
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the flake.nix file. At the end of your flake.nix (just before the final closing
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`}`), there should be a line that looks like this:
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```nix
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});
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```
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This is what terminates the `outputs` declaration from all the way at the top.
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In order to add the container configuration, you should change this to look like
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this:
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```nix
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}) // {
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};
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```
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Then we can add the container configuration to the flake:
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```nix
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}) // {
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nixosConfigurations.container = nixpkgs.lib.nixosSystem {
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system = "x86_64-linux";
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modules = [
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({pkgs, ...}: {
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# Only allow this to boot as a container
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boot.isContainer = true;
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networking.hostName = "gohello";
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# Allow nginx through the firewall
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networking.firewall.allowedTCPPorts = [ 80 ];
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services.nginx.enable = true;
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})
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];
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};
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};
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```
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This will create a container (with the hostname "gohello") that starts nginx and
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allows traffic to go to nginx on TCP port 80. You can start up the container
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with the `nixos-container` command:
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```console
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$ sudo nixos-container create gohello --flake .#container
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host IP is 10.233.1.1, container IP is 10.233.1.2
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```
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Then you can start the container with this command:
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```console
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$ sudo nixos-container start gohello
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```
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And then we can try to connect to nginx to see if it's working:
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```console
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$ curl http://10.233.1.2
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<!DOCTYPE html>
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<html>
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<head>
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<title>Welcome to nginx!</title>
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<style>
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body {}
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width: 35em;
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margin: 0 auto;
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font-family: Tahoma, Verdana, Arial, sans-serif;
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}
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</style>
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</head>
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<body>
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<h1>Welcome to nginx!</h1>
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<p>If you see this page, the nginx web server is successfully installed and
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working. Further configuration is required.</p>
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<p>For online documentation and support please refer to
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<a href="http://nginx.org/">nginx.org</a>.<br/>
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Commercial support is available at
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<a href="http://nginx.com/">nginx.com</a>.</p>
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<p><em>Thank you for using nginx.</em></p>
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</body>
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</html>
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```
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We have nginx!
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Now that we have our container to test with, let's write the configuration for
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the service. At a basic level we need the following things:
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- A systemd unit for orchestrating the HTTP server process
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- nginx configuration to reverse proxy to that HTTP server
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Above the container definition, add this basic NixOS module template:
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```nix
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nixosModule = { config, lib, pkgs, ... }:
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with lib;
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let cfg = config.xeserv.services.gohello;
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in {
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options.xeserv.services.gohello = {
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enable = mkEnableOption "Enables the gohello HTTP service";
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};
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config = mkIf cfg.enable {
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};
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};
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```
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This will create a NixOS module that will only be enabled when the configuration
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setting `xeserv.services.gohello.enable` is set to `true`. Everything else we do
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here will build on this.
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[You can and probably do want to change the namespace `xeserv` here, it is a
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placeholder that is not likely to conflict with anything
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else.](conversation://Mara/happy)
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Create a basic systemd service with this template:
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```nix
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config = mkIf cfg.enable {
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systemd.services."xeserv.gohello" = {
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wantedBy = [ "multi-user.target" ];
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serviceConfig = let pkg = self.packages.${system}.default;
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in {
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Restart = "on-failure";
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ExecStart = "${pkg}/bin/web-server";
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DynamicUser = "yes";
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RuntimeDirectory = "xeserv.gohello";
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RuntimeDirectoryMode = "0755";
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StateDirectory = "xeserv.gohello";
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StateDirectoryMode = "0700";
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CacheDirectory = "xeserv.gohello";
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CacheDirectoryMode = "0750";
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};
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};
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};
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```
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[NOTE: You will want to be sure to do the following things to your copy of
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gohello: <ul><li>Move the definition of `defaultPackage` into the `packages` attribute set with the name `default` </li><li>Update `defaultApp` and the other entries to point to `self.packages.${system}.default` instead of `self.defaultPackage.${system}`</li></ul> We have updated previous articles and the template
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accordingly.](conversation://Mara/hacker)
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This will do the following things:
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- Start the service on boot (`multi-user.target` fires once the system is "fully
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booted" and the network is active)
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- Automatically restarts the service when it crashes
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- Starts our `web-server` binary when running the service
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- Creates a random user for the service
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- Creates temporary, home and cache directories for the service, makes sure that
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random user has permission to use them (with the specified directory modes
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too)
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- Enables the service automatically
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Then you need to add the nginx configuration. We want this application to have
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its own virtual host, so we will need to add that as a configuration option
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under the `enable` option:
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```nix
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domain = mkOption rec {
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type = types.str;
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default = "gohello.local.cetacean.club";
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example = default;
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description = "The domain name for gohello";
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};
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```
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[Pro tip: `anything.local.cetacean.club` points to `127.0.0.1`. You can use this
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when testing things.](conversation://Mara/happy)
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And then we can add the nginx configuration under the systemd service definition:
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```nix
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services.nginx.virtualHosts.${cfg.domain} = {
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locations."/" = { proxyPass = "http://127.0.0.1:3031"; };
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};
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```
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Your module should look like this:
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```nix
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nixosModule = { config, lib, pkgs, ... }:
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with lib;
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let cfg = config.xeserv.services.gohello;
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in {
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options.xeserv.services.gohello = {
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enable = mkEnableOption "Enables the gohello HTTP service";
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domain = mkOption rec {
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type = types.str;
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default = "gohello.local.cetacean.club";
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example = default;
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description = "The domain name for gohello";
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};
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};
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config = mkIf cfg.enable {
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systemd.services."xeserv.gohello" = {
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wantedBy = [ "multi-user.target" ];
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serviceConfig = let pkg = self.packages.${pkgs.system}.default;
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in {
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Restart = "on-failure";
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ExecStart = "${pkg}/bin/web-server";
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DynamicUser = "yes";
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RuntimeDirectory = "xeserv.gohello";
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RuntimeDirectoryMode = "0755";
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StateDirectory = "xeserv.gohello";
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StateDirectoryMode = "0700";
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CacheDirectory = "xeserv.gohello";
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CacheDirectoryMode = "0750";
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};
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};
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services.nginx.virtualHosts.${cfg.domain} = {
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locations."/" = { proxyPass = "http://127.0.0.1:3031"; };
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};
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};
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};
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```
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Then you can add it to the container by importing our new module in its
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configuration and activating the gohello service:
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```nix
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nixosConfigurations.container = nixpkgs.lib.nixosSystem {
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system = "x86_64-linux";
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modules = [
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self.nixosModule
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({ pkgs, ... }: {
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# Only allow this to boot as a container
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boot.isContainer = true;
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# Allow nginx through the firewall
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networking.firewall.allowedTCPPorts = [ 80 ];
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services.nginx.enable = true;
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xeserv.services.gohello.enable = true;
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})
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];
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};
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```
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Then you can update the container's configuration with this command:
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```console
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$ sudo nixos-container update gohello --flake .#container
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reloading container...
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```
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And finally make a request to the gohello service running in that container:
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```console
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$ curl http://10.233.1.2 -H "Host: gohello.local.cetacean.club"
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hello world :)
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```
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[As an exercise for the reader, try adding a <a
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href="https://nixos.org/manual/nixos/stable/index.html#sec-writing-modules">nixos
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option</a> that correlates to the `--bind` flag that `gohello` uses as the TCP
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address to serve HTTP from. You will want to have the type be
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`types.port`.](conversation://Mara/hacker)
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You can delete this container with `sudo nixos-container destroy gohello` when
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you are done with it.
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These are the basics on how to use NixOS modules. Everything else you can do
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with them builds off of these fundamental ideas. Modules are templates that
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coordinate packages and configuration into your desired system state. Containers
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can let you test out modules without having to add them to your currently
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running system. Modules declare options and emit configuration based on those
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options.
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You can also consume NixOS modules from flakes using the input system, however I
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will go into more details about this at a later date. If you want more examples
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of NixOS modules, I would suggest checking out my
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[nixos-configs](https://github.com/Xe/nixos-configs) repository. I have nearly
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everything neatly modularized and configurable. If you see anything in there
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that is confusing to you, please [reach out](/contact) and ask. I am happy to
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answer your questions and your feedback will help me write future posts in this
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series.
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I also have my "next generation" flakes-based configuration experiments
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[here](https://tulpa.dev/cadey/nixos-configs) if you want to read through those.
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I have still been porting over things piecemeal, so it is not a complete replica
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of my existing configuration.
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Next time I will cover how to install NixOS to a server and deploy system
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configurations using [deploy-rs](https://github.com/serokell/deploy-rs). This
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will allow you to have your workstation build configuration for your servers and
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push out all the changes from there.
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