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Add network bridge guide to the cookbook.
Change-Id: If478196985aac7947067329957516f82bcb95ca4
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Maxim Cournoyer
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@ -77,6 +77,7 @@ manual}).
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* Packaging:: Packaging tutorials
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* System Configuration:: Customizing the GNU System
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* Containers:: Isolated environments and nested systems
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* Virtual Machines:: Virtual machines usage and configuration
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* Advanced package management:: Power to the users!
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* Software Development:: Environments, continuous integration, etc.
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* Environment management:: Control environment
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@ -155,6 +156,11 @@ Guix System Containers
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* A Database Container::
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* Container Networking::
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Virtual Machines
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* Network bridge for QEMU::
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* Routed network for libvirt::
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Advanced package management
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* Guix Profiles in Practice:: Strategies for multiple profiles and manifests.
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@ -3702,6 +3708,236 @@ sudo ip netns del $ns
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sudo ip link del $host
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@end example
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@c *********************************************************************
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@node Virtual Machines
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@chapter Virtual Machines
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Guix can produce disk images (@pxref{Invoking guix system,,, guix, GNU
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Guix Reference Manual}) that can be used with virtual machines solutions
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such as virt-manager, GNOME Boxes or the more bare QEMU, among others.
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This chapter aims to provide hands-on, practical examples that relates
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to the usage and configuration of virtual machines on a Guix System.
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@menu
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* Network bridge for QEMU::
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* Routed network for libvirt::
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@end menu
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@node Network bridge for QEMU
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@section Network bridge for QEMU
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@cindex Network bridge interface
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@cindex networking, bridge
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@cindex qemu, network bridge
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By default, QEMU uses a so-called ``user mode'' host network back-end,
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which is convenient as it does not require any configuration.
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Unfortunately, it is also quite limited. In this mode, the guest
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@abbr{VM, virtual machine} can access the network the same way the host
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would, but it cannot be reached from the host. Additionally, since the
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QEMU user networking mode relies on ICMP, ICMP-based networking tools
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such as @command{ping} do @emph{not} work in this mode. Thus, it is
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often desirable to configure a network bridge, which enables the guest
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to fully participate in the network. This is necessary, for example,
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when the guest is to be used as a server.
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@subsection Creating a network bridge interface
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There are many ways to create a network bridge. The following command
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shows how to use NetworkManager and its @command{nmcli} command line
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interface (CLI) tool, which should already be available if your
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operating system declaration is based on one of the desktop templates:
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@example sh
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# nmcli con add type bridge con-name br0 ifname br0
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@end example
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To have this bridge be part of your network, you must associate your
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network bridge with the Ethernet interface used to connect with the
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network. Assuming your interface is named @samp{enp2s0}, the following
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command can be used to do so:
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@example sh
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# nmcli con add type bridge-slave ifname enp2s0 master br0
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@end example
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@quotation Important
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Only Ethernet interfaces can be added to a bridge. For wireless
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interfaces, consider the routed network approach detailed in
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@xref{Routed network for libvirt}.
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@end quotation
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By default, the network bridge will allow your guests to obtain their IP
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address via DHCP, if available on your local network. For simplicity,
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this is what we will use here. To easily find the guests, they can be
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configured to advertise their host names via mDNS.
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@subsection Configuring the QEMU bridge helper script
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QEMU comes with a helper program to conveniently make use of a network
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bridge interface as an unprivileged user @pxref{Network options,,, QEMU,
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QEMU Documentation}. The binary must be made setuid root for proper
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operation; this can be achieved by adding it to the
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@code{setuid-programs} field of your (host) @code{operating-system}
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definition, as shown below:
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@example lisp
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(setuid-programs
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(cons (file-append qemu "/libexec/qemu-bridge-helper")
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%setuid-programs))
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@end example
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The file @file{/etc/qemu/bridge.conf} must also be made to allow the
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bridge interface, as the default is to deny all. Add the following to
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your list of services to do so:
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@example lisp
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(extra-special-file "/etc/qemu/host.conf" "allow br0\n")
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@end example
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@subsection Invoking QEMU with the right command line options
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When invoking QEMU, the following options should be provided so that the
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network bridge is used, after having selected a unique MAC address for
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the guest.
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@quotation Important
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By default, a single MAC address is used for all guests, unless
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provided. Failing to provided different MAC addresses to each virtual
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machine making use of the bridge would cause networking issues.
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@end quotation
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@example sh
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$ qemu-system-x86_64 [...] \
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-device virtio-net-pci,netdev=user0,mac=XX:XX:XX:XX:XX:XX \
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-netdev bridge,id=user0,br=br0 \
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[...]
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@end example
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To generate MAC addresses that have the QEMU registered prefix, the
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following snippet can be employed:
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@example sh
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mac_address="52:54:00:$(dd if=/dev/urandom bs=512 count=1 2>/dev/null \
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| md5sum \
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| sed -E 's/^(..)(..)(..).*$/\1:\2:\3/')"
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echo $mac_address
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@end example
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@subsection Networking issues caused by Docker
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If you use Docker on your machine, you may experience connectivity
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issues when attempting to use a network bridge, which are caused by
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Docker also relying on network bridges and configuring its own routing
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rules. The solution is add the following @code{iptables} snippet to
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your @code{operating-system} declaration:
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@example lisp
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(service iptables-service-type
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(iptables-configuration
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(ipv4-rules (plain-file "iptables.rules" "\
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*filter
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:INPUT ACCEPT [0:0]
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:FORWARD DROP [0:0]
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:OUTPUT ACCEPT [0:0]
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-A FORWARD -i br0 -o br0 -j ACCEPT
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COMMIT
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"))
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@end example
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@node Routed network for libvirt
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@section Rounted network for libvirt
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@cindex Virtual network bridge interface
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@cindex networking, virtual bridge
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@cindex libvirt, virtual network bridge
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If the machine hosting your virtual machines is connected wirelessly to
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the network, you won't be able to use a true network bridge as explained
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in the preceding section (@pxref{Network bridge for QEMU}). In this
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case, the next best option is to use a @emph{virtual} bridge with static
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routing and to configure a libvirt-powered virtual machine to use it
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(via the @command{virt-manager} GUI for example). This is similar to
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the default mode of operation of QEMU/libvirt, except that instead of
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using @abbr{NAT, Network Address Translation}, it relies on static
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routes to join the @abbr{VM, virtual machine} IP address to the
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@abbr{LAN, local area network}. This provides two-way connectivity to
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and from the virtual machine, which is needed for exposing services
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hosted on the virtual machine.
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@subsection Creating a virtual network bridge
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A virtual network bridge consists of a few components/configurations,
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such as a @abbr{TUN, network tunnel} interface, DHCP server (dnsmasq)
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and firewall rules (iptables). The @command{virsh} command, provided by
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the @code{libvirt} package, makes it very easy to create a virtual
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bridge. You first need to choose a network subnet for your virtual
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bridge; if your home LAN is in the @samp{192.168.1.0/24} network, you
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could opt to use e.g.@: @samp{192.168.2.0/24}. Define an XML file,
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e.g.@: @file{/tmp/virbr0.xml}, containing the following:
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@example
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<network>
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<name>virbr0</name>
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<bridge name="virbr0" />
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<forward mode="route"/>
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<ip address="192.168.2.0" netmask="255.255.255.0">
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<dhcp>
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<range start="192.168.2.1" end="192.168.2.254"/>
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</dhcp>
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</ip>
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</network>
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@end example
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Then create and configure the interface using the @command{virsh}
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command, as root:
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@example
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virsh net-define /tmp/virbr0.xml
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virsh net-autostart virbr0
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virsh net-start virbr0
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@end example
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The @samp{virbr0} interface should now be visible e.g.@: via the
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@samp{ip address} command. It will be automatically started every time
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your libvirt virtual machine is started.
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@subsection Configuring the static routes for your virtual bridge
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If you configured your virtual machine to use your newly created
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@samp{virbr0} virtual bridge interface, it should already receive an IP
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via DHCP such as @samp{192.168.2.15} and be reachable from the server
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hosting it, e.g.@: via @samp{ping 192.168.2.15}. There's one last
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configuration needed so that the VM can reach the external network:
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adding static routes to the network's router.
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In this example, the LAN network is @samp{192.168.1.0/24} and the router
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configuration web page may be accessible via e.g.@: the
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@url{http://192.168.1.1} page. On a router running the
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@url{https://librecmc.org/, libreCMC} firmware, you would navigate to
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the @clicksequence{Network @click{} Static Routes} page
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(@url{https://192.168.1.1/cgi-bin/luci/admin/network/routes}), and you
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would add a new entry to the @samp{Static IPv4 Routes} with the
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following information:
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@table @samp
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@item Interface
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lan
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@item Target
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192.168.2.0
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@item IPv4-Netmask
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255.255.255.0
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@item IPv4-Gateway
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@var{server-ip}
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@item Route type
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unicast
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@end table
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where @var{server-ip} is the IP address of the machine hosting the VMs,
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which should be static.
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After saving/applying this new static route, external connectivity
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should work from within your VM; you can e.g.@: run @samp{ping gnu.org}
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to verify that it functions correctly.
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@c *********************************************************************
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@node Advanced package management
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