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There's not much to read here. Look at {{manual:nixos|sec=#ch-containers|chapter=the upstream documentation on containers}} meanwhile.
Setup native [https://wiki.archlinux.org/title/systemd-nspawn systemd-nspawn] containers, which are running NixOS and are configured and managed by NixOS using the <code>containers</code> directive.
 
See [[Docker]] page for OCI container (Docker, Podman) configuration.
 
=== Configuration ===
 
The following example creates a container called webserver running a httpd web server. It will start automatically at boot and has its private network subnet.
 
{{file|/etc/nixos/configuration.nix|nix|<nowiki>
networking.nat = {
  enable = true;
  internalInterfaces = ["ve-+"];
  externalInterface = "ens3";
  # Lazy IPv6 connectivity for the container
  enableIPv6 = true;
};
 
containers.webserver = {
  autoStart = true;
  privateNetwork = true;
  hostAddress = "192.168.100.10";
  localAddress = "192.168.100.11";
  hostAddress6 = "fc00::1";
  localAddress6 = "fc00::2";
  config = { config, pkgs, lib, ... }: {
 
    services.httpd = {
      enable = true;
      adminAddr = "admin@example.org";
    };
 
    networking = {
      firewall.allowedTCPPorts = [ 80 ];
 
      # Use systemd-resolved inside the container
      # Workaround for bug https://github.com/NixOS/nixpkgs/issues/162686
      useHostResolvConf = lib.mkForce false;
    };
   
    services.resolved.enable = true;
 
    system.stateVersion = "24.11";
  };
};
</nowiki>}}
 
In order to reach the web application on the host system, we have to open [[Firewall]] port 80 and also configure NAT through <code>networking.nat</code>. The web service of the container will be available at http://192.168.100.11
 
==== Networking ====
 
{{expansion}}
 
By default, if <code>privateNetwork</code> is not set, the container shares the network with the host, enabling it to bind any port on any interface. However, when <code>privateNetwork</code> is set to <code>true</code>, the container gains its private virtual <code>eth0</code> and <code>ve-<container_name></code> on the host. This isolation is beneficial when you want the container to have its dedicated networking stack.
 
'''NAT (Network Address Translation)'''
 
<syntaxhighlight lang="nix">
</syntaxhighlight>
 
'''Bridge'''
 
<syntaxhighlight lang="nix">
networking = {
  bridges.br0.interfaces = [ "eth0s31f6" ]; # Adjust interface accordingly
 
  # Get bridge-ip with DHCP
  useDHCP = false;
  interfaces."br0".useDHCP = true;
 
  # Set bridge-ip static
  interfaces."br0".ipv4.addresses = [{
    address = "192.168.100.3";
    prefixLength = 24;
  }];
  defaultGateway = "192.168.100.1";
  nameservers = [ "192.168.100.1" ];
};
 
containers.<name> = {
  privateNetwork = true;
  hostBridge = "br0"; # Specify the bridge name
  localAddress = "192.168.100.5/24";
  config = { };
};
</syntaxhighlight>
 
=== Usage ===
 
List containers
<syntaxhighlight lang="console">
# machinectl list
</syntaxhighlight>
 
Checking the status of the container
<syntaxhighlight lang="console">
# systemctl status container@webserver
</syntaxhighlight>
 
Login into the container
<syntaxhighlight lang="console">
# nixos-container root-login webserver
</syntaxhighlight>
 
Start or stop a container
<syntaxhighlight lang="console">
# nixos-container start webserver
# nixos-container stop webserver
</syntaxhighlight>
 
Destroy a container including its file system
<syntaxhighlight lang="console">
# nixos-container destroy webserver
</syntaxhighlight>
 
View log for container<syntaxhighlight lang="console">
# journalctl -M webserver
</syntaxhighlight>Further informations are available in the {{manual:nixos|sec=#ch-containers|chapter=NixOS manual}}.
 
== Tips and tricks ==
 
==== Define and create nixos-container from a Flake file ====
We can define and create a custom container called <code>container</code> from a file stored as <code>flake.nix</code>. In this case we use the unstable branch of the nixpkgs repository as a source.<syntaxhighlight lang="nix">
{
  inputs.nixpkgs.url = "nixpkgs/nixos-unstable";
 
  outputs = { self, nixpkgs }: {
 
    nixosConfigurations.container = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules =
        [ ({ pkgs, ... }: {
            boot.isContainer = true;
 
            networking.firewall.allowedTCPPorts = [ 80 ];
 
            services.httpd = {
              enable = true;
              adminAddr = "morty@example.org";
            };
          })
        ];
    };
 
  };
}
</syntaxhighlight>To create and run that container, enter following commands. In this example the <code>flake.nix</code> file is in the same directory.<syntaxhighlight lang="console">
# nixos-container create flake-test --flake .
host IP is 10.233.4.1, container IP is 10.233.4.2
 
# nixos-container start flake-test
</syntaxhighlight>
 
==== Use agenix secrets in container ====
To add <code>agenix</code> secrets to a container bind mount the <code>ssh-host.key</code> and import the <code>agenix.nixosModule</code> and set <code>age.identityPaths</code> [https://discourse.nixos.org/t/secrets-inside-nixos-containers/34403/6 Source]<syntaxhighlight lang="nix">
{ agenix, ... }:
{
 
  containers."withSecret" = {
 
    # pass the private key to the container for agenix to decrypt the secret
    bindMounts."/etc/ssh/ssh_host_ed25519_key".isReadOnly = true;
 
    config =
      {
        config,
        lib,
        pkgs,
        ...
      }:
      {
        imports = [ agenix.nixosModules.default ]; # import agenix-module into the nixos-container
 
        age.identityPaths = [ "/etc/ssh/ssh_host_ed25519_key" ]; # isn't set automatically when openssh is not setup
        # import the secret
        age.secrets."secret-name" = {
          file = ../secrets/secret.age;
        };
      };
  };
}
</syntaxhighlight>


== Troubleshooting ==
== Troubleshooting ==


=== I have changed the host's channel and some services are acting weird ===
==== I have changed the host's channel and some services are no longer functional ====
 
'''Symptoms:'''
Acting weird could be any of those, non exhaustive symptoms:
* Lost data in PostgreSQL database
* Lost data in PostgreSQL database
* MySQL has changed its path, where it creates the database


'''Solution'''
'''Solution'''
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== See also ==
== See also ==


{{manual:nixos|sec=#ch-containers|chapter=Chapter 28. Container Management}}
* {{manual:nixos|sec=#ch-containers|chapter=Chapter on Container Management}}
* [https://blog.beardhatcode.be/2020/12/Declarative-Nixos-Containers.html Blog Article - Declarative NixOS Containers]
* [https://discourse.nixos.org/t/extra-container-run-declarative-containers-without-full-system-rebuilds/511 NixOS Discourse - Extra-container: Run declarative containers without full system rebuilds]
* [https://github.com/NixOS/nixpkgs/blob/master/pkgs/by-name/ni/nixos-container/nixos-container.pl Nixpkgs - nixos-container.pl]
* [https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/nixos-containers.nix Nixpkgs - nixos-containers.nix]
* [https://nixcademy.com/2023/08/29/nixos-nspawn/ nixos-nspawn]
* [https://github.com/tfc/nspawn-nixos tfc/nspawn-nixos]
* MicroVMs as a more isolated alternative, e.g. with https://github.com/astro/microvm.nix
[[Category:Server]]
[[Category:NixOS]]
[[Category:Container]]
Retrieved from "https://wiki.nixos.org/wiki/NixOS_Containers"