From f24b14767d362a84e6469682b4fe303b50f4b589 Mon Sep 17 00:00:00 2001 From: Maxim Cournoyer Date: Wed, 9 Jun 2021 16:25:05 -0400 Subject: Add network bridge guide to the cookbook. Change-Id: If478196985aac7947067329957516f82bcb95ca4 --- doc/guix-cookbook.texi | 236 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 236 insertions(+) (limited to 'doc') diff --git a/doc/guix-cookbook.texi b/doc/guix-cookbook.texi index cdca411706..3be1ad3243 100644 --- a/doc/guix-cookbook.texi +++ b/doc/guix-cookbook.texi @@ -77,6 +77,7 @@ manual}). * Packaging:: Packaging tutorials * System Configuration:: Customizing the GNU System * Containers:: Isolated environments and nested systems +* Virtual Machines:: Virtual machines usage and configuration * Advanced package management:: Power to the users! * Software Development:: Environments, continuous integration, etc. * Environment management:: Control environment @@ -155,6 +156,11 @@ Guix System Containers * A Database Container:: * Container Networking:: +Virtual Machines + +* Network bridge for QEMU:: +* Routed network for libvirt:: + Advanced package management * Guix Profiles in Practice:: Strategies for multiple profiles and manifests. @@ -3702,6 +3708,236 @@ sudo ip netns del $ns sudo ip link del $host @end example +@c ********************************************************************* +@node Virtual Machines +@chapter Virtual Machines + +Guix can produce disk images (@pxref{Invoking guix system,,, guix, GNU +Guix Reference Manual}) that can be used with virtual machines solutions +such as virt-manager, GNOME Boxes or the more bare QEMU, among others. + +This chapter aims to provide hands-on, practical examples that relates +to the usage and configuration of virtual machines on a Guix System. + +@menu +* Network bridge for QEMU:: +* Routed network for libvirt:: +@end menu + +@node Network bridge for QEMU +@section Network bridge for QEMU +@cindex Network bridge interface +@cindex networking, bridge +@cindex qemu, network bridge + +By default, QEMU uses a so-called ``user mode'' host network back-end, +which is convenient as it does not require any configuration. +Unfortunately, it is also quite limited. In this mode, the guest +@abbr{VM, virtual machine} can access the network the same way the host +would, but it cannot be reached from the host. Additionally, since the +QEMU user networking mode relies on ICMP, ICMP-based networking tools +such as @command{ping} do @emph{not} work in this mode. Thus, it is +often desirable to configure a network bridge, which enables the guest +to fully participate in the network. This is necessary, for example, +when the guest is to be used as a server. + +@subsection Creating a network bridge interface + +There are many ways to create a network bridge. The following command +shows how to use NetworkManager and its @command{nmcli} command line +interface (CLI) tool, which should already be available if your +operating system declaration is based on one of the desktop templates: + +@example sh +# nmcli con add type bridge con-name br0 ifname br0 +@end example + +To have this bridge be part of your network, you must associate your +network bridge with the Ethernet interface used to connect with the +network. Assuming your interface is named @samp{enp2s0}, the following +command can be used to do so: + +@example sh +# nmcli con add type bridge-slave ifname enp2s0 master br0 +@end example + +@quotation Important +Only Ethernet interfaces can be added to a bridge. For wireless +interfaces, consider the routed network approach detailed in +@xref{Routed network for libvirt}. +@end quotation + +By default, the network bridge will allow your guests to obtain their IP +address via DHCP, if available on your local network. For simplicity, +this is what we will use here. To easily find the guests, they can be +configured to advertise their host names via mDNS. + +@subsection Configuring the QEMU bridge helper script + +QEMU comes with a helper program to conveniently make use of a network +bridge interface as an unprivileged user @pxref{Network options,,, QEMU, +QEMU Documentation}. The binary must be made setuid root for proper +operation; this can be achieved by adding it to the +@code{setuid-programs} field of your (host) @code{operating-system} +definition, as shown below: + +@example lisp +(setuid-programs + (cons (file-append qemu "/libexec/qemu-bridge-helper") + %setuid-programs)) +@end example + +The file @file{/etc/qemu/bridge.conf} must also be made to allow the +bridge interface, as the default is to deny all. Add the following to +your list of services to do so: + +@example lisp +(extra-special-file "/etc/qemu/host.conf" "allow br0\n") +@end example + +@subsection Invoking QEMU with the right command line options + +When invoking QEMU, the following options should be provided so that the +network bridge is used, after having selected a unique MAC address for +the guest. + +@quotation Important +By default, a single MAC address is used for all guests, unless +provided. Failing to provided different MAC addresses to each virtual +machine making use of the bridge would cause networking issues. +@end quotation + +@example sh +$ qemu-system-x86_64 [...] \ + -device virtio-net-pci,netdev=user0,mac=XX:XX:XX:XX:XX:XX \ + -netdev bridge,id=user0,br=br0 \ + [...] +@end example + +To generate MAC addresses that have the QEMU registered prefix, the +following snippet can be employed: + +@example sh +mac_address="52:54:00:$(dd if=/dev/urandom bs=512 count=1 2>/dev/null \ + | md5sum \ + | sed -E 's/^(..)(..)(..).*$/\1:\2:\3/')" +echo $mac_address +@end example + +@subsection Networking issues caused by Docker + +If you use Docker on your machine, you may experience connectivity +issues when attempting to use a network bridge, which are caused by +Docker also relying on network bridges and configuring its own routing +rules. The solution is add the following @code{iptables} snippet to +your @code{operating-system} declaration: + +@example lisp +(service iptables-service-type + (iptables-configuration + (ipv4-rules (plain-file "iptables.rules" "\ +*filter +:INPUT ACCEPT [0:0] +:FORWARD DROP [0:0] +:OUTPUT ACCEPT [0:0] +-A FORWARD -i br0 -o br0 -j ACCEPT +COMMIT +")) +@end example + +@node Routed network for libvirt +@section Rounted network for libvirt +@cindex Virtual network bridge interface +@cindex networking, virtual bridge +@cindex libvirt, virtual network bridge + +If the machine hosting your virtual machines is connected wirelessly to +the network, you won't be able to use a true network bridge as explained +in the preceding section (@pxref{Network bridge for QEMU}). In this +case, the next best option is to use a @emph{virtual} bridge with static +routing and to configure a libvirt-powered virtual machine to use it +(via the @command{virt-manager} GUI for example). This is similar to +the default mode of operation of QEMU/libvirt, except that instead of +using @abbr{NAT, Network Address Translation}, it relies on static +routes to join the @abbr{VM, virtual machine} IP address to the +@abbr{LAN, local area network}. This provides two-way connectivity to +and from the virtual machine, which is needed for exposing services +hosted on the virtual machine. + +@subsection Creating a virtual network bridge + +A virtual network bridge consists of a few components/configurations, +such as a @abbr{TUN, network tunnel} interface, DHCP server (dnsmasq) +and firewall rules (iptables). The @command{virsh} command, provided by +the @code{libvirt} package, makes it very easy to create a virtual +bridge. You first need to choose a network subnet for your virtual +bridge; if your home LAN is in the @samp{192.168.1.0/24} network, you +could opt to use e.g.@: @samp{192.168.2.0/24}. Define an XML file, +e.g.@: @file{/tmp/virbr0.xml}, containing the following: + +@example + + virbr0 + + + + + + + + +@end example + +Then create and configure the interface using the @command{virsh} +command, as root: + +@example +virsh net-define /tmp/virbr0.xml +virsh net-autostart virbr0 +virsh net-start virbr0 +@end example + +The @samp{virbr0} interface should now be visible e.g.@: via the +@samp{ip address} command. It will be automatically started every time +your libvirt virtual machine is started. + +@subsection Configuring the static routes for your virtual bridge + +If you configured your virtual machine to use your newly created +@samp{virbr0} virtual bridge interface, it should already receive an IP +via DHCP such as @samp{192.168.2.15} and be reachable from the server +hosting it, e.g.@: via @samp{ping 192.168.2.15}. There's one last +configuration needed so that the VM can reach the external network: +adding static routes to the network's router. + +In this example, the LAN network is @samp{192.168.1.0/24} and the router +configuration web page may be accessible via e.g.@: the +@url{http://192.168.1.1} page. On a router running the +@url{https://librecmc.org/, libreCMC} firmware, you would navigate to +the @clicksequence{Network @click{} Static Routes} page +(@url{https://192.168.1.1/cgi-bin/luci/admin/network/routes}), and you +would add a new entry to the @samp{Static IPv4 Routes} with the +following information: + +@table @samp +@item Interface +lan +@item Target +192.168.2.0 +@item IPv4-Netmask +255.255.255.0 +@item IPv4-Gateway +@var{server-ip} +@item Route type +unicast +@end table + +where @var{server-ip} is the IP address of the machine hosting the VMs, +which should be static. + +After saving/applying this new static route, external connectivity +should work from within your VM; you can e.g.@: run @samp{ping gnu.org} +to verify that it functions correctly. @c ********************************************************************* @node Advanced package management -- cgit v1.2.3