mirror of
https://github.com/zrepl/zrepl.git
synced 2024-11-25 01:44:43 +01:00
117 lines
4.5 KiB
ReStructuredText
117 lines
4.5 KiB
ReStructuredText
.. highlight:: bash
|
|
|
|
.. _transport:
|
|
|
|
Transports
|
|
==========
|
|
|
|
A transport provides an authenticated `io.ReadWriteCloser <https://golang.org/pkg/io/#ReadWriteCloser>`_ to the RPC layer.
|
|
(An ``io.ReadWriteCloser`` is essentially a bidirectional reliable communication channel.)
|
|
|
|
Currently, only the ``ssh+stdinserver`` transport is supported.
|
|
|
|
.. _transport-ssh+stdinserver:
|
|
|
|
``ssh+stdinserver`` Transport
|
|
-----------------------------
|
|
|
|
The way the ``ssh+stdinserver`` transport works is inspired by `git shell <https://git-scm.com/docs/git-shell>`_ and `Borg Backup <https://borgbackup.readthedocs.io/en/stable/deployment.html>`_.
|
|
It is provided by the Go package ``github.com/problame/go-netssh``.
|
|
The config excerpts are taken from the :ref:`tutorial` which you should complete before reading further.
|
|
|
|
.. _transport-ssh+stdinserver-serve:
|
|
|
|
Serve Mode
|
|
~~~~~~~~~~
|
|
|
|
::
|
|
|
|
jobs:
|
|
- name: pull_backup
|
|
type: source
|
|
serve:
|
|
type: stdinserver
|
|
client_identity: backup-srv.example.com
|
|
...
|
|
|
|
The serving job opens a UNIX socket named after ``client_identity`` in the runtime directory, e.g. ``/var/run/zrepl/stdinserver/backup-srv.example.com``.
|
|
|
|
On the same machine, the ``zrepl stdinserver $client_identity`` command connects to that socket.
|
|
For example, ``zrepl stdinserver backup-srv.example.com`` connects to the UNIX socket ``/var/run/zrepl/stdinserver/backup-srv.example.com``.
|
|
|
|
It then passes its stdin and stdout file descriptors to the zrepl daemon via *cmsg(3)*.
|
|
zrepl daemon in turn combines them into an ``io.ReadWriteCloser``:
|
|
a ``Write()`` turns into a write to stdout, a ``Read()`` turns into a read from stdin.
|
|
|
|
Interactive use of the ``stdinserver`` subcommand does not make much sense.
|
|
However, we can force its execution when a user with a particular SSH pubkey connects via SSH.
|
|
This can be achieved with an entry in the ``authorized_keys`` file of the serving zrepl daemon.
|
|
|
|
::
|
|
|
|
# for OpenSSH >= 7.2
|
|
command="zrepl stdinserver CLIENT_IDENTITY",restrict CLIENT_SSH_KEY
|
|
# for older OpenSSH versions
|
|
command="zrepl stdinserver CLIENT_IDENTITY",no-port-forwarding,no-X11-forwarding,no-pty,no-agent-forwarding,no-user-rc CLIENT_SSH_KEY
|
|
|
|
* CLIENT_IDENTITY is substituted with ``backup-srv.example.com`` in our example
|
|
* CLIENT_SSH_KEY is substituted with the public part of the SSH keypair specified in the ``connect`` directive on the connecting host.
|
|
|
|
.. NOTE::
|
|
|
|
You may need to adjust the ``PermitRootLogin`` option in ``/etc/ssh/sshd_config`` to ``forced-commands-only`` or higher for this to work.
|
|
Refer to sshd_config(5) for details.
|
|
|
|
To recap, this is of how client authentication works with the ``ssh+stdinserver`` transport:
|
|
|
|
* Connections to the ``client_identity`` UNIX socket are blindly trusted by zrepl daemon.
|
|
* Thus, the runtime directory must be private to the zrepl user (checked by zrepl daemon)
|
|
* The admin of the host with the serving zrepl daemon controls the ``authorized_keys`` file.
|
|
* Thus, the administrator controls the mapping ``PUBKEY -> CLIENT_IDENTITY``.
|
|
|
|
.. _transport-ssh+stdinserver-connect:
|
|
|
|
Connect Mode
|
|
~~~~~~~~~~~~
|
|
|
|
::
|
|
|
|
jobs:
|
|
- name: pull_app-srv
|
|
type: pull
|
|
connect:
|
|
type: ssh+stdinserver
|
|
host: app-srv.example.com
|
|
user: root
|
|
port: 22
|
|
identity_file: /etc/zrepl/ssh/identity
|
|
options: # optional, default [], `-o` arguments passed to ssh
|
|
- "Compression=on"
|
|
dial_timeout: # optional, default 10s, max time.Duration until initial handshake is completed
|
|
|
|
The connecting zrepl daemon
|
|
|
|
#. Creates a pipe
|
|
#. Forks
|
|
#. In the forked process
|
|
|
|
#. Replaces forked stdin and stdout with the corresponding pipe ends
|
|
#. Executes the ``ssh`` binary found in ``$PATH``.
|
|
|
|
#. The identity file (``-i``) is set to ``$identity_file``.
|
|
#. The remote user, host and port correspond to those configured.
|
|
#. Further options can be specified using the ``options`` field, which appends each entry in the list to the command line using ``-o $entry``.
|
|
|
|
#. Wraps the pipe ends in an ``io.ReadWriteCloser`` and uses it for RPC.
|
|
|
|
|
|
As discussed in the section above, the connecting zrepl daemon expects that ``zrepl stdinserver $client_identity`` is executed automatically via an ``authorized_keys`` file entry.
|
|
|
|
The ``known_hosts`` file used by the ssh command must contain an entry for the serving host, e.g., ``app-srv.example.com`` in the example above.
|
|
|
|
.. NOTE::
|
|
|
|
The environment variables of the underlying SSH process are cleared. ``$SSH_AUTH_SOCK`` will not be available.
|
|
It is suggested to create a separate, unencrypted SSH key solely for that purpose.
|
|
|