[PATCH v2 2/3] docs: Document SSH proxy
Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
---
docs/docs.rst | 3 ++
docs/meson.build | 1 +
docs/nss.rst | 7 +++++
docs/ssh-proxy.rst | 68 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 79 insertions(+)
create mode 100644 docs/ssh-proxy.rst
diff --git a/docs/docs.rst b/docs/docs.rst
index f57164b9e3..1a958e9cc7 100644
--- a/docs/docs.rst
+++ b/docs/docs.rst
@@ -47,6 +47,9 @@ Deployment / operation
`Hooks <hooks.html>`__
Hooks for system specific management
+`SSH Proxy <ssh-proxy.html>`__
+ Enable SSH into guests over a VSOCK
+
`NSS module <nss.html>`__
Enable domain host name translation to IP addresses
diff --git a/docs/meson.build b/docs/meson.build
index 87d728213c..2dda59f978 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -97,6 +97,7 @@ docs_rst_files = [
'python',
'remote',
'securityprocess',
+ 'ssh-proxy',
'storage',
'strategy',
'styleguide',
diff --git a/docs/nss.rst b/docs/nss.rst
index 8f98330221..53955a3278 100644
--- a/docs/nss.rst
+++ b/docs/nss.rst
@@ -152,3 +152,10 @@ If there's no record for either of the aforementioned commands,
it's very likely
that NSS module won't find anything and vice versa. As of ``v3.0.0`` libvirt
provides ``libvirt_guest`` NSS module that doesn't have this limitation.
However, the statement is still true for the ``libvirt`` NSS module.
+
+Alternatives
+------------
+
+As of ``v10.3.0`` libvirt implements an `SSH proxy <ssh-proxy.html>`__ which
+doesn't require any network interface to SSH into the guest as SSH flows
+through a VSOCK device.
diff --git a/docs/ssh-proxy.rst b/docs/ssh-proxy.rst
new file mode 100644
index 0000000000..830668f8cd
--- /dev/null
+++ b/docs/ssh-proxy.rst
@@ -0,0 +1,68 @@
+=================
+Libvirt SSH proxy
+=================
+
+Sometimes it's necessary to run some commands inside a guest. While libvirt
+already provides a `NSS module <nss.html>`__ that can translate guest name to
+IP address it has some limitations (e.g. guest has to have a network interface
+plugged into a libvirt managed network). To resolve some of these limitations,
+libvirt offers a SSH proxy. It consists of a SSH client config file
+(``/etc/ssh/ssh_config.d/30-libvirt-ssh-proxy.conf``) and a small binary. Both
+are automatically installed by ``libvirt-client`` package. After running:
+
+``ssh user@qemu/virtualMachine``
+
+the configuration file instructs SSH client to start the binary helper which
+finds a VSOCK device inside the ``virtualMachine`` and establishes a connection
+to it.
+
+For now, only QEMU domains are implemented and the lookup of the
+``virtualMachine`` is done under ``qemu:///system`` URI first, followed by
+``qemu:///session``. Accepted values for ``virtualMachine`` are: domain name
+(as reported by e.g. `virsh list`), domain UUID and finally domain ID.
+
+Guest OS requirements
+---------------------
+
+It is obvious that the SSH daemon inside the guest needs to be configured to
+listen for incoming connections on a VSOCK. There are couple of ways to achieve
+this:
+
+* Run systemd-v256 or newer inside the guest.
+
+ In this release, systemd started to deploy ``systemd-ssh-generator`` which
+ should configure socket activation for SSHD automagically.
+
+* Set up socket activation for VSOCK.
+
+ We can take an inspiration in the unit file generated by
+ ``systemd-ssh-generator``:
+
+::
+
+ [Unit]
+ Description=OpenSSH Server Socket (systemd-ssh-generator, AF_VSOCK)
+ Documentation=man:systemd-ssh-generator(8)
+ Wants=ssh-access.target
+ Before=ssh-access.target
+
+ [Socket]
+ ListenStream=vsock::22
+ Accept=yes
+ PollLimitIntervalSec=30s
+ PollLimitBurst=50
+
+* Run a service that forwards VSOCK <=> SSHD communication
+
+ For instance:
+
+::
+
+ socat VSOCK-LISTEN:22,reuseaddr,fork TCP:localhost:22
+
+Libvirt domain XML configuration
+--------------------------------
+
+Since the SSH proxy uses a VSOCK to communicate with the SSH daemon running
+inside the guest, it is a must to configure VSOCK in the `domain XML
+<formatdomain.html#vsock>`__.
--
2.43.2