6f7aaf10a5
Note that this causes the name of the host-side interface to change from c-<name> to ve-<name>.
242 lines
8 KiB
XML
242 lines
8 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xml:id="ch-containers">
|
||
|
||
<title>Containers</title>
|
||
|
||
<para>NixOS allows you to easily run other NixOS instances as
|
||
<emphasis>containers</emphasis>. Containers are a light-weight
|
||
approach to virtualisation that runs software in the container at the
|
||
same speed as in the host system. NixOS containers share the Nix store
|
||
of the host, making container creation very efficient.</para>
|
||
|
||
<warning><para>Currently, NixOS containers are not perfectly isolated
|
||
from the host system. This means that a user with root access to the
|
||
container can do things that affect the host. So you should not give
|
||
container root access to untrusted users.</para></warning>
|
||
|
||
<para>NixOS containers can be created in two ways: imperatively, using
|
||
the command <command>nixos-container</command>, and declaratively, by
|
||
specifying them in your <filename>configuration.nix</filename>. The
|
||
declarative approach implies that containers get upgraded along with
|
||
your host system when you run <command>nixos-rebuild</command>, which
|
||
is often not what you want. By contrast, in the imperative approach,
|
||
containers are configured and updated independently from the host
|
||
system.</para>
|
||
|
||
|
||
<section><title>Imperative container management</title>
|
||
|
||
<para>We’ll cover imperative container management using
|
||
<command>nixos-container</command> first. You create a container with
|
||
identifier <literal>foo</literal> as follows:
|
||
|
||
<screen>
|
||
$ nixos-container create foo
|
||
</screen>
|
||
|
||
This creates the container’s root directory in
|
||
<filename>/var/lib/containers/foo</filename> and a small configuration
|
||
file in <filename>/etc/containers/foo.conf</filename>. It also builds
|
||
the container’s initial system configuration and stores it in
|
||
<filename>/nix/var/nix/profiles/per-container/foo/system</filename>. You
|
||
can modify the initial configuration of the container on the command
|
||
line. For instance, to create a container that has
|
||
<command>sshd</command> running, with the given public key for
|
||
<literal>root</literal>:
|
||
|
||
<screen>
|
||
$ nixos-container create foo --config 'services.openssh.enable = true; \
|
||
users.extraUsers.root.openssh.authorizedKeys.keys = ["ssh-dss AAAAB3N…"];'
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
<para>Creating a container does not start it. To start the container,
|
||
run:
|
||
|
||
<screen>
|
||
$ nixos-container start foo
|
||
</screen>
|
||
|
||
This command will return as soon as the container has booted and has
|
||
reached <literal>multi-user.target</literal>. On the host, the
|
||
container runs within a systemd unit called
|
||
<literal>container@<replaceable>container-name</replaceable>.service</literal>.
|
||
Thus, if something went wrong, you can get status info using
|
||
<command>systemctl</command>:
|
||
|
||
<screen>
|
||
$ systemctl status container@foo
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
<para>If the container has started succesfully, you can log in as
|
||
root using the <command>root-login</command> operation:
|
||
|
||
<screen>
|
||
$ nixos-container root-login foo
|
||
[root@foo:~]#
|
||
</screen>
|
||
|
||
Note that only root on the host can do this (since there is no
|
||
authentication). You can also get a regular login prompt using the
|
||
<command>login</command> operation, which is available to all users on
|
||
the host:
|
||
|
||
<screen>
|
||
$ nixos-container login foo
|
||
foo login: alice
|
||
Password: ***
|
||
</screen>
|
||
|
||
With <command>nixos-container run</command>, you can execute arbitrary
|
||
commands in the container:
|
||
|
||
<screen>
|
||
$ nixos-container run foo -- uname -a
|
||
Linux foo 3.4.82 #1-NixOS SMP Thu Mar 20 14:44:05 UTC 2014 x86_64 GNU/Linux
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
<para>There are several ways to change the configuration of the
|
||
container. First, on the host, you can edit
|
||
<literal>/var/lib/container/<replaceable>name</replaceable>/etc/nixos/configuration.nix</literal>,
|
||
and run
|
||
|
||
<screen>
|
||
$ nixos-container update foo
|
||
</screen>
|
||
|
||
This will build and activate the new configuration. You can also
|
||
specify a new configuration on the command line:
|
||
|
||
<screen>
|
||
$ nixos-container update foo --config 'services.httpd.enable = true; \
|
||
services.httpd.adminAddr = "foo@example.org";'
|
||
|
||
$ curl http://$(nixos-container show-ip foo)/
|
||
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">…
|
||
</screen>
|
||
|
||
However, note that this will overwrite the container’s
|
||
<filename>/etc/nixos/configuration.nix</filename>.</para>
|
||
|
||
<para>Alternatively, you can change the configuration from within the
|
||
container itself by running <command>nixos-rebuild switch</command>
|
||
inside the container. Note that the container by default does not have
|
||
a copy of the NixOS channel, so you should run <command>nix-channel
|
||
--update</command> first.</para>
|
||
|
||
<para>Containers can be stopped and started using
|
||
<literal>nixos-container stop</literal> and <literal>nixos-container
|
||
start</literal>, respectively, or by using
|
||
<command>systemctl</command> on the container’s service unit. To
|
||
destroy a container, including its file system, do
|
||
|
||
<screen>
|
||
$ nixos-container destroy foo
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
</section>
|
||
|
||
|
||
<section><title>Declarative container specification</title>
|
||
|
||
<para>You can also specify containers and their configuration in the
|
||
host’s <filename>configuration.nix</filename>. For example, the
|
||
following specifies that there shall be a container named
|
||
<literal>database</literal> running PostgreSQL:
|
||
|
||
<programlisting>
|
||
containers.database =
|
||
{ config =
|
||
{ config, pkgs, ... }:
|
||
{ services.postgresql.enable = true;
|
||
services.postgresql.package = pkgs.postgresql92;
|
||
};
|
||
};
|
||
</programlisting>
|
||
|
||
If you run <literal>nixos-rebuild switch</literal>, the container will
|
||
be built and started. If the container was already running, it will be
|
||
updated in place, without rebooting.</para>
|
||
|
||
<para>By default, declarative containers share the network namespace
|
||
of the host, meaning that they can listen on (privileged)
|
||
ports. However, they cannot change the network configuration. You can
|
||
give a container its own network as follows:
|
||
|
||
<programlisting>
|
||
containers.database =
|
||
{ privateNetwork = true;
|
||
hostAddress = "192.168.100.10";
|
||
localAddress = "192.168.100.11";
|
||
};
|
||
</programlisting>
|
||
|
||
This gives the container a private virtual Ethernet interface with IP
|
||
address <literal>192.168.100.11</literal>, which is hooked up to a
|
||
virtual Ethernet interface on the host with IP address
|
||
<literal>192.168.100.10</literal>. (See the next section for details
|
||
on container networking.)</para>
|
||
|
||
<para>To disable the container, just remove it from
|
||
<filename>configuration.nix</filename> and run <literal>nixos-rebuild
|
||
switch</literal>. Note that this will not delete the root directory of
|
||
the container in <literal>/var/lib/containers</literal>.</para>
|
||
|
||
</section>
|
||
|
||
|
||
<section><title>Networking</title>
|
||
|
||
<para>When you create a container using <literal>nixos-container
|
||
create</literal>, it gets it own private IPv4 address in the range
|
||
<literal>10.233.0.0/16</literal>. You can get the container’s IPv4
|
||
address as follows:
|
||
|
||
<screen>
|
||
$ nixos-container show-ip foo
|
||
10.233.4.2
|
||
|
||
$ ping -c1 10.233.4.2
|
||
64 bytes from 10.233.4.2: icmp_seq=1 ttl=64 time=0.106 ms
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
<para>Networking is implemented using a pair of virtual Ethernet
|
||
devices. The network interface in the container is called
|
||
<literal>eth0</literal>, while the matching interface in the host is
|
||
called <literal>ve-<replaceable>container-name</replaceable></literal>
|
||
(e.g., <literal>ve-foo</literal>). The container has its own network
|
||
namespace and the <literal>CAP_NET_ADMIN</literal> capability, so it
|
||
can perform arbitrary network configuration such as setting up
|
||
firewall rules, without affecting or having access to the host’s
|
||
network.</para>
|
||
|
||
<para>By default, containers cannot talk to the outside network. If
|
||
you want that, you should set up Network Address Translation (NAT)
|
||
rules on the host to rewrite container traffic to use your external
|
||
IP address. This can be accomplished using the following configuration
|
||
on the host:
|
||
|
||
<programlisting>
|
||
networking.nat.enable = true;
|
||
networking.nat.internalInterfaces = ["ve-+"];
|
||
networking.nat.externalInterface = "eth0";
|
||
</programlisting>
|
||
where <literal>eth0</literal> should be replaced with the desired
|
||
external interface. Note that <literal>ve-+</literal> is a wildcard
|
||
that matches all container interfaces.</para>
|
||
|
||
</section>
|
||
|
||
|
||
</chapter>
|
||
|