zrepl/docs/tutorial.rst
2017-11-11 23:25:12 +01:00

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.. include:: global.rst.inc
.. _tutorial:
Tutorial
========
This tutorial shows how zrepl can be used to implement a ZFS-based pull backup.
We assume the following scenario:
* Production server ``app-srv`` with filesystems to back up:
* ``zroot/var/db``
* ``zroot/usr/home`` and all its child filesystems
* **except** ``zroot/usr/home/paranoid`` belonging to a user doing backups themselves
* Backup server ``backup-srv`` with
* Filesystem ``storage/zrepl/pull/app-srv`` + children dedicated to backups of ``app-srv``
Our backup solution should fulfill the following requirements:
* Periodically snapshot the filesystems on ``app-srv`` *every 10 minutes*
* Incrementally replicate these snapshots to ``storage/zrepl/pull/app-srv/*`` on ``backup-srv``
* Keep only very few snapshots on ``app-srv`` to save disk space
* Keep a fading history (24 hourly, 30 daily, 6 monthly) of snapshots on ``backup-srv``
Analysis
--------
We can model this situation as two jobs:
* A **source job** on ``app-srv``
* Creates the snapshots
* Keeps a short history of snapshots to enable incremental replication to ``backup-srv``
* Accepts connections from ``backup-srv``
* A **pull job** on ``backup-srv``
* Connects to the ``zrepl daemon`` process on ``app-srv``
* Pulls the snapshots to ``storage/zrepl/pull/app-srv/*``
* Fades out snapshots in ``storage/zrepl/pull/app-srv/*`` as they age
Why doesn't the **pull job** create the snapshots before pulling?
As is the case with all distributed systems, the link between ``app-srv`` and ``backup-srv`` might be down for an hour or two.
We do not want to sacrifice our required backup resolution of 10 minute intervals for a temporary connection outage.
When the link comes up again, ``backup-srv`` will happily catch up the 12 snapshots taken by ``app-srv`` in the meantime, without
a gap in our backup history.
Install zrepl
-------------
Follow the :ref:`OS-specific installation instructions <installation>` and come back here.
Configure ``backup-srv``
------------------------
We define a **pull job** named ``pull_app-srv`` in the |mainconfig|: ::
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
interval: 10m
mapping: {
"<":"storage/zrepl/pull/app-srv"
}
initial_repl_policy: most_recent
snapshot_prefix: zrepl_pull_backup_
prune:
policy: grid
grid: 1x1h(keep=all) | 24x1h | 35x1d | 6x30d
The ``connect`` section instructs the zrepl daemon to use the ``stdinserver`` transport:
``backup-srv`` will connect to the specified SSH server and expect ``zrepl stdinserver CLIENT_IDENTITY`` instead of the shell on the other side.
It uses the private key specified at ``connect.identity_file`` which we still need to create:::
cd /etc/zrepl
mkdir -p ssh
chmod 0700 ssh
ssh-keygen -t ed25519 -N '' -f /etc/zrepl/ssh/identity
Note that most use cases do not benefit from separate keypairs per remote endpoint.
Thus, it is sufficient to create one keypair and use it for all ``connect`` directives on one host.
Learn more about :ref:`transport-ssh+stdinserver` transport and the :ref:`pull job <job-pull>` format.
.. _tutorial-configure-app-srv:
Configure ``app-srv``
---------------------
We define a corresponding **source job** named ``pull_backup`` in the |mainconfig|:::
jobs:
- name: pull_backup
type: source
serve:
type: stdinserver
client_identity: backup-srv.example.com
filesystems: {
"zroot/var/db": "ok",
"zroot/usr/home<": "ok",
"zroot/usr/home/paranoid": "!",
}
snapshot_prefix: zrepl_pull_backup_
interval: 10m
prune:
policy: grid
grid: 1x1d(keep=all)
The ``serve`` section corresponds to the ``connect`` section in the configuration of ``backup-srv``.
We now want to authenticate ``backup-srv`` before allowing it to pull data.
This is done by limiting SSH connections from ``backup-srv`` to execute the ``stdinserver`` subcommand.
Open ``/root/.ssh/authorized_keys`` and add either of the the following lines.::
# for OpenSSH >= 7.2
command="zrepl stdinserver backup-srv.example.com",restrict CLIENT_SSH_KEY
# for older OpenSSH versions
command="zrepl stdinserver backup-srv.example.com",no-port-forwarding,no-X11-forwarding,no-pty,no-agent-forwarding,no-user-rc CLIENT_SSH_KEY
.. ATTENTION::
Replace CLIENT_SSH_KEY with the contents of ``/etc/zrepl/ssh/identity.pub`` from ``app-srv``.
Mind the trailing ``.pub`` in the filename.
The entries **must** be on a single line, including the replaced CLIENT_SSH_KEY.
.. HINT::
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.
The argument ``backup-srv.example.com`` is the client identity of ``backup-srv`` as defined in ``jobs.serve.client_identity``.
Again, both :ref:`transport-ssh+stdinserver` transport and the :ref:`job-source` format are documented.
Apply Configuration Changes
---------------------------
We need to restart the zrepl daemon on **both** ``app-srv`` and ``backup-srv``.
This is :ref:`OS-specific <install-restarting>`.
Watch it Work
-------------
A common setup is to ``watch`` the log output and ``zfs list`` of snapshots on both machines.
If you like tmux, here is a handy script that works on FreeBSD:::
pkg install gnu-watch tmux
tmux new-window
tmux split-window "tail -f /var/log/zrepl.log"
tmux split-window "gnu-watch 'zfs list -t snapshot -o name,creation -s creation | grep zrepl_pull_backup_'"
tmux select-layout tiled
The Linux equivalent might look like this::
# make sure tmux is installed & let's assume you use systemd + journald
tmux new-window
tmux split-window "journalctl -f -u zrepl.service"
tmux split-window "watch 'zfs list -t snapshot -o name,creation -s creation | grep zrepl_pull_backup_'"
tmux select-layout tiled
Summary
-------
Congratulations, you have a working pull backup. Where to go next?
* Read more about :ref:`configuration format, options & job types <configuration_toc>`
* Learn about :ref:`implementation details <implementation_toc>` of zrepl.