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Add support for lightweight NixOS containers

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You can now say:

  systemd.containers.foo.config =
    { services.openssh.enable = true;
      services.openssh.ports = [ 2022 ];
      users.extraUsers.root.openssh.authorizedKeys.keys = [ "ssh-dss ..." ];
    };

which defines a NixOS instance with the given configuration running
inside a lightweight container.

You can also manage the configuration of the container independently
from the host:

  systemd.containers.foo.path = "/nix/var/nix/profiles/containers/foo";

where "path" is a NixOS system profile.  It can be created/updated by
doing:

  $ nix-env --set -p /nix/var/nix/profiles/containers/foo \
      -f '<nixos>' -A system -I nixos-config=foo.nix

The container configuration (foo.nix) should define

  boot.isContainer = true;

to optimise away the building of a kernel and initrd.  This is done
automatically when using the "config" route.

On the host, a lightweight container appears as the service
"container-<name>.service".  The container is like a regular NixOS
(virtual) machine, except that it doesn't have its own kernel.  It has
its own root file system (by default /var/lib/containers/<name>), but
shares the Nix store of the host (as a read-only bind mount).  It also
has access to the network devices of the host.

Currently, if the configuration of the container changes, running
"nixos-rebuild switch" on the host will cause the container to be
rebooted.  In the future we may want to send some message to the
container so that it can activate the new container configuration
without rebooting.

Containers are not perfectly isolated yet.  In particular, the host's
/sys/fs/cgroup is mounted (writable!) in the guest.
This commit is contained in:
Eelco Dolstra 2013-11-27 16:54:20 +01:00
parent 57f145a7f8
commit 9ee30cd9b5
10 changed files with 172 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
nixos/lib/eval-config.nix
View File

@ -8,6 +8,7 @@
, extraArgs ? {}
, modules
, check ? true
, prefix ? []
}:
let extraArgs_ = extraArgs; pkgs_ = pkgs; system_ = system; in
@ -17,6 +18,7 @@ rec {
# Merge the option definitions in all modules, forming the full
# system configuration.
inherit (pkgs.lib.evalModules {
inherit prefix;
modules = modules ++ baseModules;
args = extraArgs;
check = check && options.environment.checkConfigurationOptions.value;
@ -48,7 +50,7 @@ rec {
let
system = if nixpkgsOptions.system != "" then nixpkgsOptions.system else system_;
nixpkgsOptions = (import ./eval-config.nix {
inherit system extraArgs modules;
inherit system extraArgs modules prefix;
# For efficiency, leave out most NixOS modules; they don't
# define nixpkgs.config, so it's pointless to evaluate them.
baseModules = [ ../modules/misc/nixpkgs.nix ];

5
nixos/modules/module-list.nix
View File

@ -247,11 +247,11 @@
./system/boot/kexec.nix
./system/boot/loader/efi.nix
./system/boot/loader/generations-dir/generations-dir.nix
./system/boot/loader/gummiboot/gummiboot.nix
./system/boot/loader/raspberrypi/raspberrypi.nix
./system/boot/loader/grub/grub.nix
./system/boot/loader/grub/memtest.nix
./system/boot/loader/gummiboot/gummiboot.nix
./system/boot/loader/init-script/init-script.nix
./system/boot/loader/raspberrypi/raspberrypi.nix
./system/boot/luksroot.nix
./system/boot/modprobe.nix
./system/boot/shutdown.nix
@ -276,6 +276,7 @@
./tasks/scsi-link-power-management.nix
./tasks/swraid.nix
./testing/service-runner.nix
./virtualisation/containers.nix
./virtualisation/libvirtd.nix
#./virtualisation/nova.nix
./virtualisation/virtualbox-guest.nix

11
nixos/modules/services/hardware/udev.nix
View File

@ -209,7 +209,7 @@ in
###### implementation
config = {
config = mkIf (!config.boot.isContainer) {
services.udev.extraRules = nixosRules;
@ -231,9 +231,16 @@ in
boot.extraModprobeConfig = "options firmware_class path=${config.hardware.firmware}";
system.activationScripts.clearHotplug =
system.activationScripts.udevd =
''
echo "" > /proc/sys/kernel/hotplug
# Regenerate the hardware database /var/lib/udev/hwdb.bin
# whenever systemd changes.
if [ ! -e /var/lib/udev/prev-systemd -o "$(readlink /var/lib/udev/prev-systemd)" != ${config.systemd.package} ]; then
echo "regenerating udev hardware database..."
${config.systemd.package}/bin/udevadm hwdb --update && ln -sfn ${config.systemd.package} /var/lib/udev/prev-systemd
fi
'';
};

27
nixos/modules/system/activation/top-level.nix
View File

@ -34,16 +34,24 @@ let
in ''
mkdir $out
if [ ! -f ${kernelPath} ]; then
echo "The bootloader cannot find the proper kernel image."
echo "(Expecting ${kernelPath})"
false
fi
# Containers don't have their own kernel or initrd. They boot
# directly into stage 2.
${optionalString (!config.boot.isContainer) ''
if [ ! -f ${kernelPath} ]; then
echo "The bootloader cannot find the proper kernel image."
echo "(Expecting ${kernelPath})"
false
fi
ln -s ${kernelPath} $out/kernel
ln -s ${config.system.modulesTree} $out/kernel-modules
ln -s ${kernelPath} $out/kernel
ln -s ${config.system.modulesTree} $out/kernel-modules
ln -s ${config.system.build.initialRamdisk}/initrd $out/initrd
echo -n "$kernelParams" > $out/kernel-params
ln -s ${config.system.build.initialRamdisk}/initrd $out/initrd
ln -s ${config.hardware.firmware} $out/firmware
''}
echo "$activationScript" > $out/activate
substituteInPlace $out/activate --subst-var out
@ -56,9 +64,7 @@ let
ln -s ${config.system.build.etc}/etc $out/etc
ln -s ${config.system.path} $out/sw
ln -s "$systemd" $out/systemd
ln -s ${config.hardware.firmware} $out/firmware
echo -n "$kernelParams" > $out/kernel-params
echo -n "$configurationName" > $out/configuration-name
echo -n "systemd ${toString config.systemd.package.interfaceVersion}" > $out/init-interface-version
echo -n "$nixosVersion" > $out/nixos-version
@ -92,7 +98,6 @@ let
systemd = config.systemd.package;
inherit children;
kernelParams = config.boot.kernelParams;
installBootLoader =
config.system.build.installBootLoader
or "echo 'Warning: do not know how to make this configuration bootable; please enable a boot loader.' 1>&2; true";

2
nixos/modules/system/boot/kernel.nix
View File

@ -145,7 +145,7 @@ in
###### implementation
config = {
config = mkIf (!config.boot.isContainer) {
system.build = { inherit kernel; };

2
nixos/modules/system/boot/loader/grub/grub.nix
View File

@ -44,7 +44,7 @@ in
boot.loader.grub = {
enable = mkOption {
default = true;
default = !config.boot.isContainer;
type = types.bool;
description = ''
Whether to enable the GNU GRUB boot loader.

2
nixos/modules/system/boot/modprobe.nix
View File

@ -66,7 +66,7 @@ with pkgs.lib;
###### implementation
config = {
config = mkIf (!config.boot.isContainer) {
environment.etc = singleton
{ source = pkgs.writeText "modprobe.conf"

2
nixos/modules/system/boot/stage-1.nix
View File

@ -328,7 +328,7 @@ in
};
config = {
config = mkIf (!config.boot.isContainer) {
assertions = singleton
{ assertion = any (fs: fs.mountPoint == "/") (attrValues config.fileSystems);

7
nixos/modules/system/boot/systemd.nix
View File

@ -604,13 +604,6 @@ in
mkdir -p /var/log/journal
chmod 0755 /var/log/journal
# Regenerate the hardware database /var/lib/udev/hwdb.bin
# whenever systemd changes.
if [ ! -e /var/lib/udev/prev-systemd -o "$(readlink /var/lib/udev/prev-systemd)" != ${systemd} ]; then
echo "regenerating udev hardware database..."
${systemd}/bin/udevadm hwdb --update && ln -sfn ${systemd} /var/lib/udev/prev-systemd
fi
# Make all journals readable to users in the wheel and adm
# groups, in addition to those in the systemd-journal group.
# Users can always read their own journals.

137
nixos/modules/virtualisation/containers.nix Normal file
View File

@ -0,0 +1,137 @@
{ config, pkgs, ... }:
with pkgs.lib;
{
options = {
boot.isContainer = mkOption {
type = types.bool;
default = false;
description = ''
Whether this NixOS machine is a lightweight container running
in another NixOS system.
'';
};
systemd.containers = mkOption {
type = types.attrsOf (types.submodule (
{ config, options, name, ... }:
{
options = {
root = mkOption {
type = types.path;
description = ''
The root directory of the container.
'';
};
config = mkOption {
description = ''
A specification of the desired configuration of this
container, as a NixOS module.
'';
};
path = mkOption {
type = types.path;
example = "/nix/var/nix/profiles/containers/webserver";
description = ''
As an alternative to specifying
<option>config</option>, you can specify the path to
the evaluated NixOS system configuration, typically a
symlink to a system profile.
'';
};
};
config = mkMerge
[ { root = mkDefault "/var/lib/containers/${name}";
}
(mkIf options.config.isDefined {
path = (import ../../lib/eval-config.nix {
modules =
let extraConfig =
{ boot.isContainer = true;
security.initialRootPassword = "!";
networking.hostName = mkDefault name;
};
in [ extraConfig config.config ];
prefix = [ "systemd" "containers" name ];
}).config.system.build.toplevel;
})
];
}));
default = {};
example = literalExample
''
{ webserver =
{ root = "/containers/webserver";
path = "/nix/var/nix/profiles/webserver";
};
database =
{ root = "/containers/database";
config =
{ config, pkgs, ... }:
{ services.postgresql.enable = true;
services.postgresql.package = pkgs.postgresql92;
};
};
}
'';
description = ''
A set of NixOS system configurations to be run as lightweight
containers. Each container appears as a service
<literal>container-<replaceable>name</replaceable></literal>
on the host system, allowing it to be started and stopped via
<command>systemctl</command> .
'';
};
};
config = {
systemd.services = mapAttrs' (name: container: nameValuePair "container-${name}"
{ description = "Container '${name}'";
wantedBy = [ "multi-user.target" ];
unitConfig.RequiresMountsFor = [ container.root ];
preStart =
''
mkdir -p -m 0755 ${container.root}/etc
if ! [ -e ${container.root}/etc/os-release ]; then
touch ${container.root}/etc/os-release
fi
'';
serviceConfig.ExecStart =
"${config.systemd.package}/bin/systemd-nspawn -M ${name} -D ${container.root} --bind-ro=/nix ${container.path}/init";
preStop =
''
pid="$(cat /sys/fs/cgroup/systemd/machine/${name}.nspawn/system/tasks 2> /dev/null)"
if [ -n "$pid" ]; then
# Send the RTMIN+3 signal, which causes the container
# systemd to start halt.target.
echo "killing container systemd, PID = $pid"
kill -RTMIN+3 $pid
# Wait for the container to exit. We can't let systemd
# do this because it will send a signal to the entire
# cgroup.
for ((n = 0; n < 180; n++)); do
if ! kill -0 $pid 2> /dev/null; then break; fi
sleep 1
done
fi
'';
}) config.systemd.containers;
};
}