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