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== Native NixOS containers ==
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.


It is possible to configure 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.


=== Installation ===
=== Configuration ===


The following example creates a container called <code>nextcloud</code> running the web application [[Nextcloud]]. It will start automatically at boot and has its private network subnet.
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>
{{file|/etc/nixos/configuration.nix|nix|<nowiki>
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};
};


containers.nextcloud = {
containers.webserver = {
   autoStart = true;
   autoStart = true;
   privateNetwork = true;
   privateNetwork = true;
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   hostAddress6 = "fc00::1";
   hostAddress6 = "fc00::1";
   localAddress6 = "fc00::2";
   localAddress6 = "fc00::2";
   config = { config, pkgs, ... }: {
   config = { config, pkgs, lib, ... }: {


     services.nextcloud = {
     services.httpd = {
       enable = true;
       enable = true;
       package = pkgs.nextcloud27;
       adminAddr = "admin@example.org";
      hostName = "localhost";
      config.adminpassFile = "${pkgs.writeText "adminpass" "test123"}"; # DON'T DO THIS IN PRODUCTION - the password file will be world-readable in the Nix Store!
     };
     };


     system.stateVersion = "23.05";
     networking = {
      firewall.allowedTCPPorts = [ 80 ];


    networking = {
      firewall = {
        enable = true;
        allowedTCPPorts = [ 80 ];
      };
       # Use systemd-resolved inside the container
       # Use systemd-resolved inside the container
       # Workaround for bug https://github.com/NixOS/nixpkgs/issues/162686
       # Workaround for bug https://github.com/NixOS/nixpkgs/issues/162686
       useHostResolvConf = mkForce false;
       useHostResolvConf = lib.mkForce false;
     };
     };
      
      
     services.resolved.enable = true;
     services.resolved.enable = true;


    system.stateVersion = "24.11";
   };
   };
};
};
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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
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 ===
=== Usage ===
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Checking the status of the container
Checking the status of the container
<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
# systemctl status container@nextcloud
# systemctl status container@webserver
</syntaxhighlight>
</syntaxhighlight>


Login into the container
Login into the container
<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
# nixos-container root-login nextcloud
# nixos-container root-login webserver
</syntaxhighlight>
</syntaxhighlight>


Start or stop a container
Start or stop a container
<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
# nixos-container start nextcloud
# nixos-container start webserver
# nixos-container stop nextcloud
# nixos-container stop webserver
</syntaxhighlight>
</syntaxhighlight>


Destroy a container including its file system
Destroy a container including its file system
<syntaxhighlight lang="console">
<syntaxhighlight lang="console">
# nixos-container destroy nextcloud
# nixos-container destroy webserver
</syntaxhighlight>
</syntaxhighlight>


Further informations are available in the {{manual:nixos|sec=#ch-containers|chapter=NixOS manual}}.
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";


== Declarative docker containers ==
  outputs = { self, nixpkgs }: {


Example config:
     nixosConfigurations.container = nixpkgs.lib.nixosSystem {
  { config, pkgs, ... }:
       system = "x86_64-linux";
  {
      modules =
     config.virtualisation.oci-containers.containers = {
         [ ({ pkgs, ... }: {
       hackagecompare = {
            boot.isContainer = true;
        image = "chrissound/hackagecomparestats-webserver:latest";
 
         ports = ["127.0.0.1:3010:3010"];
            networking.firewall.allowedTCPPorts = [ 80 ];
        volumes = [
 
          "/root/hackagecompare/packageStatistics.json:/root/hackagecompare/packageStatistics.json"
            services.httpd = {
        ];
              enable = true;
        cmd = [
              adminAddr = "morty@example.org";
          "--base-url"
            };
           "\"/hackagecompare\""
           })
         ];
         ];
    };
  };
}
</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 no longer functional ===
==== I have changed the host's channel and some services are no longer functional ====
 
'''Symptoms:'''
'''Symptoms:'''
* Lost data in PostgreSQL database
* Lost data in PostgreSQL database
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* [https://blog.beardhatcode.be/2020/12/Declarative-Nixos-Containers.html Blog Article - Declarative NixOS Containers]
* [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://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/tools/virtualization/nixos-container/nixos-container.pl Nixpkgs - nixos-container.pl]
* [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://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://nixcademy.com/2023/08/29/nixos-nspawn/ nixos-nspawn]
* https://github.com/tfc/nspawn-nixos]
* [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:Server]]
[[Category:NixOS]]
[[Category:NixOS]]
[[Category:Container]]
Retrieved from "https://wiki.nixos.org/wiki/NixOS_Containers"