docs: Add instructions to run libvirt with (#4578)

Also organize other "how to run cloud-init locally" content better.

Fixes GH-4608

doc/rtd/howto/run_cloud_init_locally.rst

@@ -19,8 +19,11 @@ The ``NoCloud`` datasouce allows users to provide their own user data,
 metadata, or network configuration directly to an instance without running a
 network service. This is helpful for launching local cloud images with QEMU.
 
-The following is an example of creating the local disk using the
-:command:`genisoimage` command:
+Create your configuration
+-------------------------
+We will leave the network-config and meta-data files empty, but populate
+user-data with a cloud-init configuration. You may edit the network and
+meta-data files if you have a config to provide.
 
 .. code-block:: shell-session
 
@@ -32,10 +35,12 @@ The following is an example of creating the local disk using the
     chpasswd:
       expire: False
     ssh_pwauth: True
-    ssh_authorized_keys:
-      - ssh-rsa AAAA...UlIsqdaO+w==
     EOF
 
+Create an iso disk
+------------------
+This disk is used to pass configuration to cloud-init. Create it with the
+:command:`genisoimage` command:
 
 .. code-block:: shell-session
 
@@ -44,24 +49,35 @@ The following is an example of creating the local disk using the
         -volid cidata -rational-rock -joliet \
         user-data meta-data network-config
 
-See the :ref:`network_config_v2` page for details on the format and config of
-network configuration. To learn more about the possible values for metadata,
-check out the :ref:`datasource_nocloud` page.
 
-The resulting :file:`seed.img` can then be passed along to a cloud image
-containing ``cloud-init``. Below is an example of passing the :file:`seed.img`
-with QEMU:
+Download a cloud image
+----------------------
+Download a Ubuntu image to run:
+
+.. code-block:: shell-session
+
+    wget https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img
+
+Boot the image with the iso attached
+------------------------------------
+Pass the :file:`seed.img` with QEMU:
 
 .. code-block:: shell-session
 
     $ qemu-system-x86_64 -m 1024 -net nic -net user \
-        -hda ubuntu-20.04-server-cloudimg-amd64.img \
+        -hda jammy-server-cloudimg-amd64.img \
         -hdb seed.img
 
 The now-booted image will allow for login using the password provided above.
 
 For additional configuration, users can provide much more detailed
-configuration, including network configuration and metadata:
+configuration in the empty files network-config and meta-data.
+
+.. note::
+
+    See the :ref:`network_config_v2` page for details on the format and config
+    of network configuration. To learn more about the possible values for
+    metadata, check out the :ref:`datasource_nocloud` page.
 
 LXD
 ===
@@ -109,6 +125,50 @@ See the LXD `Instance Configuration`_ docs for more info about configuration
 values or the LXD `Custom Network Configuration`_ document for more about
 custom network config.
 
+Libvirt
+=======
+
+Libvirt is tool for managing virtual machines and containers.
+
+Create your configuration
+-------------------------
+
+We will leave the network-config and meta-data files empty, but populate
+user-data with a cloud-init configuration. You may edit the network and
+meta-data files if you have a config to provide.
+
+.. code-block:: shell-session
+
+    $ touch network-config
+    $ touch meta-data
+    $ cat >user-data <<EOF
+    #cloud-config
+    password: password
+    chpasswd:
+      expire: False
+    ssh_pwauth: True
+    EOF
+
+Download a cloud image
+----------------------
+Download a Ubuntu image to run:
+
+.. code-block:: shell-session
+
+    wget https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img
+
+
+Create an instance
+------------------
+
+.. code-block:: shell-session
+
+    virt-install --name cloud-init-001 --memory 4000 --noreboot \
+        --os-variant detect=on,name=ubuntujammy \
+        --disk=size=10,backing_store="$(pwd)/jammy-server-cloudimg-amd64.img" \
+        --cloud-init user-data="$(pwd)/user-data,meta-data=$(pwd)/meta-data,network-config=$(pwd)/network-config"
+
+
 Multipass
 =========
 `Multipass`_ is a cross-platform tool for launching Ubuntu VMs across Linux,