Add support for creating a bridge device for use by VMs for Ubuntu

README.md

@@ -34,6 +34,34 @@ host ~ $ sudo usermod -a -G libvirt $(whoami)
 host ~ $ newgrp libvirt
 ```
 
+##### Bridged Network on Ubuntu 22.04
+
+NOTE: This only works for wired interfaces.
+
+In some cases, it's useful to bridge a VM to your local network. This allows accessing the VM
+on your the same LAN as your Linux host. The following script adds a bridge, `virbr1`, to your host
+ethernet interface. It sets it up for DHCP v4, which allows the VM to receive an IP address from
+your local router. The script then creates a bridged network named `host-bridge` for use by libvirt.
+
+First, find the name of your ethernet interface with `ip a` or `ifconfig`.
+
+Then run the script. In this example, the ethernet interface is named `enp4s0`.
+
+```
+ sudo ./create-host-bridge.sh enp4s0
+```
+
+Lastly, apply the network interface changes to the host. 
+
+**IMPORTANT**: This will cause you to lose your connection temporarily if you are SSH'd into the box.
+
+```
+sudo netplan apply
+```
+
+
+This bridge can be used by VMs by changing their configuration to use `NETWORK=host-bridge`.
+
 #### Macintosh
 
 Install VMware Fusion.  These instructions have been tested with VMware Fusion
@@ -75,6 +103,7 @@ are stored in `config/defaults.sh`:
 host ~/helios-engvm $ cat config/defaults.sh
 VM=helios
 POOL=default
+NETWORK=default
 INPUT_IMAGE=helios-qemu-ttya-full.raw
 SIZE=30G
 VCPU=2
@@ -88,6 +117,9 @@ host ~/helios-engvm $ echo 'VCPU=8' >config/big.sh
 host ~/helios-engvm $ echo 'MEM=$(( 8 * 1024 * 1024 ))' >>config/big.sh
 ```
 
+Note: If you created a host bridge for an ubuntu system, you can use that bridge by setting
+`NETWORK=host-bridge` in the configuration similar to the examples above.
+
 You can now create a virtual machine.  If you provide an argument, it is
 the name of one of the override configuration files you have created within
 the `config` directory, e.g.,

config/defaults.sh

@@ -1,5 +1,6 @@
 VM=helios
 POOL=default
+NETWORK=default
 INPUT_IMAGE=helios-qemu-ttya-full.raw
 SIZE=30G
 VCPU=2

create.sh

@@ -165,7 +165,7 @@ cat > "$TOP/tmp/$VM.xml" <<EOF
       <target dev="vdb" bus="virtio"/>
     </disk>
     <interface type="network">
-      <source network="default"/>
+      <source network="$NETWORK"/>
       <model type="virtio"/>
     </interface>
     <serial type="pty"/>

ubuntu/create-host-bridge.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+
+set -o xtrace
+set -o pipefail
+set -o errexit
+
+if [[ -z $1 ]]; then
+    echo "Argument for ethernet interface required"
+    echo "example: $0 eth0"
+    exit 1
+fi
+
+IFACE="$1"
+
+# Backup the old netplan if it exists
+OLD_CFG="/etc/netplan/00-installer-config.yaml"
+if [[ -f "$OLD_CFG" ]]; then
+    mv $OLD_CFG $OLD_CFG.bak
+fi
+
+# Install the new netplan
+NEW_CFG="/etc/netplan/00-helios-engvm.yaml"
+cat >"$NEW_CFG" <<EOF
+network:
+  ethernets:
+    $IFACE:
+      dhcp4: false
+  version: 2
+  bridges:
+      virbr1:
+          dhcp4: yes
+          interfaces:
+              - $IFACE
+          parameters:
+              stp: true
+EOF
+
+# Setup a bridge device so VMs can reach the LAN
+virsh net-define host-bridge.xml
+virsh net-start host-bridge
+virsh net-autostart host-bridge
+

ubuntu/host-bridge.xml

@@ -0,0 +1,5 @@
+<network>
+  <name>host-bridge</name>
+  <forward mode="bridge"/>
+  <bridge name="virbr1"/>
+</network>