docs: continous_server_backup: simplify by removing need for recv.placeholder

closes https://github.com/zrepl/zrepl/pull/552
fixes https://github.com/zrepl/zrepl/issues/551

Signed-off-by: Andrew Gunnerson <chillermillerlong@hotmail.com>
Co-authored-by: Christian Schwarz <me@cschwarz.com>

README.md

@@ -1,11 +1,12 @@
 [![GitHub license](https://img.shields.io/github/license/zrepl/zrepl.svg)](https://github.com/zrepl/zrepl/blob/master/LICENSE)
-[![Language: Go](https://img.shields.io/badge/language-Go-6ad7e5.svg)](https://golang.org/)
+[![Language: Go](https://img.shields.io/badge/lang-Go-6ad7e5.svg)](https://golang.org/)
 [![User Docs](https://img.shields.io/badge/docs-web-blue.svg)](https://zrepl.github.io)
-[![Support me on Patreon](https://img.shields.io/badge/dynamic/json?color=yellow&label=Patreon&query=data.attributes.patron_count&suffix=%20patrons&url=https%3A%2F%2Fwww.patreon.com%2Fapi%2Fcampaigns%2F3095079)](https://patreon.com/zrepl)
+[![Support me on Patreon](https://img.shields.io/badge/dynamic/json?color=yellow&label=Patreon&query=data.attributes.patron_count&url=https%3A%2F%2Fwww.patreon.com%2Fapi%2Fcampaigns%2F3095079)](https://patreon.com/zrepl)
 [![Donate via GitHub Sponsors](https://img.shields.io/static/v1?label=Sponsor&message=%E2%9D%A4&logo=GitHub&style=flat&color=yellow)](https://github.com/sponsors/problame)
 [![Donate via Liberapay](https://img.shields.io/liberapay/patrons/zrepl.svg?logo=liberapay)](https://liberapay.com/zrepl/donate)
 [![Donate via PayPal](https://img.shields.io/badge/donate-paypal-yellow.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=R5QSXJVYHGX96)
 [![Twitter](https://img.shields.io/twitter/url/https/github.com/zrepl/zrepl.svg?style=social)](https://twitter.com/intent/tweet?text=Wow:&url=https%3A%2F%2Fgithub.com%2Fzrepl%2Fzrepl)
+[![Chat](https://img.shields.io/badge/chat-matrix-blue.svg)](https://matrix.to/#/#zrepl:matrix.org)
 
 # zrepl
 zrepl is a one-stop ZFS backup & replication solution.

config/samples/quickstart_continuous_server_backup_receiver.yml

@@ -9,7 +9,4 @@ jobs:
       key: "/etc/zrepl/backups.key"
       client_cns:
         - "prod"
-  recv:
-    placeholder:
-      encryption: inherit # use 'off' if sender uses send.encrypted
   root_fs: "storage/zrepl/sink"

config/samples/quickstart_continuous_server_backup_sender.yml

@@ -9,8 +9,8 @@ jobs:
     key:  /etc/zrepl/prod.key
     server_cn: "backups"
   filesystems: {
-    "zroot/var/db": true,
-    "zroot/usr/home<": true,
+    "zroot<": true,
+    "zroot/var/tmp<": false,
     "zroot/usr/home/paranoid": false
   }
   snapshotting:

config/samples/quickstart_fan_out_replication_source.yml

@@ -0,0 +1,59 @@
+jobs:
+# Separate job for snapshots and pruning
+- name: snapshots
+  type: snap
+  filesystems:
+    'tank<': true # all filesystems
+  snapshotting:
+    type: periodic
+    prefix: zrepl_
+    interval: 10m
+  pruning:
+    keep:
+      # Keep non-zrepl snapshots
+      - type: regex
+        negate: true
+        regex: '^zrepl_'
+      # Time-based snapshot retention
+      - type: grid
+        grid: 1x1h(keep=all) | 24x1h | 30x1d | 12x30d
+        regex: '^zrepl_'
+
+# Source job for target B
+- name: target_b
+  type: source
+  serve:
+    type: tls
+    listen: :8888
+    ca: /etc/zrepl/b.example.com.crt
+    cert: /etc/zrepl/a.example.com.crt
+    key: /etc/zrepl/a.example.com.key
+    client_cns:
+      - b.example.com
+  filesystems:
+    'tank<': true # all filesystems
+  # Snapshots are handled by the separate snap job
+  snapshotting:
+    type: manual
+
+# Source job for target C
+- name: target_c
+  type: source
+  serve:
+    type: tls
+    listen: :8889
+    ca: /etc/zrepl/c.example.com.crt
+    cert: /etc/zrepl/a.example.com.crt
+    key: /etc/zrepl/a.example.com.key
+    client_cns:
+      - c.example.com
+  filesystems:
+    'tank<': true # all filesystems
+  # Snapshots are handled by the separate snap job
+  snapshotting:
+    type: manual
+
+# Source jobs for remaining targets. Each one should listen on a different port
+# and reference the correct certificate and client CN.
+# - name: target_c
+#   ...

config/samples/quickstart_fan_out_replication_target.yml

@@ -0,0 +1,30 @@
+jobs:
+# Pull from source server A
+- name: source_a
+  type: pull
+  connect:
+    type: tls
+    # Use the correct port for this specific client (eg. B is 8888, C is 8889, etc.)
+    address: a.example.com:8888
+    ca: /etc/zrepl/a.example.com.crt
+    # Use the correct key pair for this specific client
+    cert: /etc/zrepl/b.example.com.crt
+    key: /etc/zrepl/b.example.com.key
+    server_cn: a.example.com
+  root_fs: pool0/backup
+  interval: 10m
+  pruning:
+    keep_sender:
+      # Source does the pruning in its snap job
+      - type: regex
+        regex: '.*'
+    # Receiver-side pruning can be configured as desired on each target server
+    keep_receiver:
+      # Keep non-zrepl snapshots
+      - type: regex
+        negate: true
+        regex: '^zrepl_'
+      # Time-based snapshot retention
+      - type: grid
+        grid: 1x1h(keep=all) | 24x1h | 30x1d | 12x30d
+        regex: '^zrepl_'

docs/configuration/overview.rst

@@ -248,7 +248,7 @@ Limitations
 Multiple Jobs & More than 2 Machines
 ------------------------------------
 
-The quick-start guides focus on simple setups with a single sender and a single receiver.
+Most users are served well with a single sender and a single receiver job.
 This section documents considerations for more complex setups.
 
 .. ATTENTION::
@@ -288,11 +288,46 @@ This section might be relevant to users who wish to *fan-in* (N machines replica
 
 **Working setups**:
 
-* N ``push`` identities, 1 ``sink`` (as long as the different push jobs have a different :ref:`client identity <overview-passive-side--client-identity>`)
+* **Fan-in: N servers replicated to one receiver, disjoint dataset trees.**
 
-  * ``sink`` constrains each client to a disjoint sub-tree of the sink-side dataset hierarchy ``${root_fs}/${client_identity}``.
+  * This is the common use case of a centralized backup server.
+
+  * Implementation:
+
+    * N ``push`` jobs (one per sender server), 1 ``sink`` (as long as the different push jobs have a different :ref:`client identity <overview-passive-side--client-identity>`)
+    * N ``source`` jobs (one per sender server), N ``pull`` on the receiver server (unique names, disjoing  ``root_fs``)
+
+  * The ``sink`` job automatically constrains each client to a disjoint sub-tree of the sink-side dataset hierarchy ``${root_fs}/${client_identity}``.
     Therefore, the different clients cannot interfere.
 
+  * The ``pull`` job only pulls from one host, so it's up to the zrepl user to ensure that the different ``pull`` jobs don't interfere.
+
+.. _fan-out-replication:
+
+* **Fan-out: 1 server replicated to N receivers**
+
+  * Can be implemented either in a pull or push fashion.
+
+    * **pull setup**: 1 ``pull`` job on each receiver server, each with a corresponding **unique** ``source`` job on the sender server.
+    * **push setup**: 1 ``sink`` job on each receiver server, each with a corresponding **unique** ``push`` job on the sender server.
+
+  * It is critical that we have one sending-side job (``source``, ``push``) per receiver.
+    The reason is that :ref:`zrepl's ZFS abstractions <zrepl-zfs-abstractions>` (``zrepl zfs-abstraction list``) include the name of the ``source``/``push`` job, but not the receive-side job name or client identity (see :issue:`380`).
+    As a counter-example, suppose we used multiple ``pull`` jobs with only one ``source`` job.
+    All ``pull`` jobs would share the same :ref:`replication cursor bookmark <replication-cursor-and-last-received-hold>` and trip over each other, breaking incremental replication guarantees quickly.
+    The anlogous problem exists for 1 ``push`` to N ``sink`` jobs.
+
+  * The ``filesystems`` matched by the sending side jobs (``source``, ``push``) need not necessarily be disjoint.
+    For this to work, we need to avoid interference between snapshotting and pruning of the different sending jobs.
+    The solution is to centralize sender-side snapshot management in a separate ``snap`` job.
+    Snapshotting in the ``source``/``push`` job should then be disabled (``type: manual``).
+    And sender-side pruning (``keep_sender``) needs to be disabled in the active side (``pull`` / ``push``), since that'll be done by the ``snap job``.
+
+  * **Restore limitations**: when restoring from one of the ``pull`` targets (e.g., using ``zfs send -R``), the replication cursor bookmarks don't exist on the restored system.
+    This can break incremental replication to all other receive-sides after restore.
+
+  * See :ref:`the fan-out replication quick-start guide <quickstart-fan-out-replication>` for an example of this setup.
+
 
 **Setups that do not work**:
 

docs/global.rst.inc

@@ -5,7 +5,7 @@
 
 .. |GitHub license| image:: https://img.shields.io/github/license/zrepl/zrepl.svg
    :target: https://github.com/zrepl/zrepl/blob/master/LICENSE
-.. |Language: Go| image:: https://img.shields.io/badge/language-Go-6ad7e5.svg
+.. |Language: Go| image:: https://img.shields.io/badge/lang-Go-6ad7e5.svg
    :target: https://golang.org/
 .. |User Docs| image:: https://img.shields.io/badge/docs-web-blue.svg
    :target: https://zrepl.github.io
@@ -13,13 +13,14 @@
    :target: https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=R5QSXJVYHGX96
 .. |Donate via Liberapay| image:: https://img.shields.io/liberapay/patrons/zrepl.svg?logo=liberapay
    :target: https://liberapay.com/zrepl/donate
-.. |Donate via Patreon| image:: https://img.shields.io/badge/dynamic/json?color=yellow&label=Patreon&query=data.attributes.patron_count&suffix=%20patrons&url=https%3A%2F%2Fwww.patreon.com%2Fapi%2Fcampaigns%2F3095079
+.. |Donate via Patreon| image:: https://img.shields.io/badge/dynamic/json?color=yellow&label=Patreon&query=data.attributes.patron_count&url=https%3A%2F%2Fwww.patreon.com%2Fapi%2Fcampaigns%2F3095079
    :target: https://www.patreon.com/zrepl
 .. |Donate via GitHub Sponsors| image:: https://img.shields.io/static/v1?label=Sponsor&message=%E2%9D%A4&logo=GitHub&style=flat&color=yellow
    :target: https://github.com/sponsors/problame
 .. |Twitter| image:: https://img.shields.io/twitter/url/https/github.com/zrepl/zrepl.svg?style=social
    :target: https://twitter.com/intent/tweet?text=Wow:&url=https%3A%2F%2Fgithub.com%2Fzrepl%2Fzrepl
-
+.. |Matrix| image:: https://img.shields.io/badge/chat-matrix-blue.svg
+   :target: https://matrix.to/#/#zrepl:matrix.org
 
 .. |serve-transport| replace:: :ref:`serve specification<transport>`
 .. |connect-transport| replace:: :ref:`connect specification<transport>`

docs/index.rst

@@ -5,7 +5,7 @@
 
 .. include:: global.rst.inc
 
-|GitHub license| |Language: Go| |Twitter| |Donate via Patreon| |Donate via GitHub Sponsors| |Donate via Liberapay| |Donate via PayPal|
+|GitHub license| |Language: Go| |Twitter| |Donate via Patreon| |Donate via GitHub Sponsors| |Donate via Liberapay| |Donate via PayPal| |Matrix|
 
 
 zrepl - ZFS replication
@@ -137,5 +137,6 @@ Table of Contents
    pr
    changelog
    GitHub Repository & Issue Tracker <https://github.com/zrepl/zrepl>
+   Chat: Matrix <https://matrix.to/#/#zrepl:matrix.org>
    supporters
 

docs/quickstart.rst

@@ -33,6 +33,7 @@ Keep the :ref:`full config documentation <configuration_toc>` handy if a config
 
    quickstart/continuous_server_backup
    quickstart/backup_to_external_disk
+   quickstart/fan_out_replication
 
 Use ``zrepl configcheck`` to validate your configuration.
 No output indicates that everything is fine.

docs/quickstart/continuous_server_backup.rst

@@ -9,13 +9,13 @@ This config example shows how we can backup our ZFS-based server to another mach
 
 * Production server ``prod`` 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
+  * The entire pool ``zroot``
+  * except ``zroot/var/tmp`` and all child datasets of it
+  * and except ``zroot/usr/home/paranoid`` which belongs to a user doing backups themselves.
 
-* Backup server ``backups`` with
+* Backup server ``backups`` with a dataset sub-tree for use by zrepl:
 
-  * Filesystem ``storage/zrepl/sink/prod`` + children dedicated to backups of ``prod``
+  * In our example, that will be ``storage/zrepl/sink/prod``.
 
 Our backup solution should fulfill the following requirements:
 

docs/quickstart/fan_out_replication.rst

@@ -0,0 +1,93 @@
+.. include:: ../global.rst.inc
+
+.. _quickstart-fan-out-replication:
+
+Fan-out replication
+===================
+
+This quick-start example demonstrates how to implement a fan-out replication setup where datasets on a server (A) are replicated to multiple targets (B, C, etc.).
+
+This example uses multiple ``source`` jobs on server A and ``pull`` jobs on the target servers.
+
+.. WARNING::
+
+   Before implementing this setup, please see the caveats listed in the :ref:`fan-out replication configuration overview <fan-out-replication>`.
+
+Overview
+--------
+
+On the source server (A), there should be:
+
+* A ``snap`` job
+
+  * Creates the snapshots
+  * Handles the pruning of snapshots
+
+* A ``source`` job for target B
+
+  * Accepts connections from server B and B only
+
+* Further ``source`` jobs for each additional target (C, D, etc.)
+
+  * Listens on a unique port
+  * Only accepts connections from the specific target
+
+On each target server, there should be:
+
+* A ``pull`` job that connects to the corresponding ``source`` job on A
+
+  * ``prune_sender`` should keep all snapshots since A's ``snap`` job handles the pruning
+  * ``prune_receiver`` can be configured as appropriate on each target server
+
+Generate TLS Certificates
+-------------------------
+
+Mutual TLS via the :ref:`TLS client authentication transport <transport-tcp+tlsclientauth>` can be used to secure the connections between the servers. In this example, a self-signed certificate is created for each server without setting up a CA.
+
+.. code-block:: bash
+
+    source=a.example.com
+    targets=(
+        b.example.com
+        c.example.com
+        # ...
+    )
+
+    for server in "${source}" "${targets[@]}"; do
+        openssl req -x509 -sha256 -nodes \
+            -newkey rsa:4096 \
+            -days 365 \
+            -keyout "${server}.key" \
+            -out "${server}.crt" \
+            -addext "subjectAltName = DNS:${server}" \
+            -subj "/CN=${server}"
+    done
+
+    # Distribute each host's keypair
+    for server in "${source}" "${targets[@]}"; do
+        ssh root@"${server}" mkdir /etc/zrepl
+        scp "${server}".{crt,key} root@"${server}":/etc/zrepl/
+    done
+
+    # Distribute target certificates to the source
+    scp "${targets[@]/%/.crt}" root@"${source}":/etc/zrepl/
+
+    # Distribute source certificate to the targets
+    for server in "${targets[@]}"; do
+        scp "${source}.crt" root@"${server}":/etc/zrepl/
+    done
+
+Configure source server A
+-------------------------
+
+.. literalinclude:: ../../config/samples/quickstart_fan_out_replication_source.yml
+
+Configure each target server
+----------------------------
+
+.. literalinclude:: ../../config/samples/quickstart_fan_out_replication_target.yml
+
+Go Back To Quickstart Guide
+---------------------------
+
+:ref:`Click here <quickstart-apply-config>` to go back to the quickstart guide.

util/optionaldeadline/optionaldeadline_test.go

@@ -9,9 +9,11 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/zrepl/zrepl/util/chainlock"
+	"github.com/zrepl/zrepl/util/zreplcircleci"
 )
 
 func TestContextWithOptionalDeadline(t *testing.T) {
+	zreplcircleci.SkipOnCircleCI(t, "test relies on predictably low scheduler latency")
 
 	ctx := context.Background()
 	cctx, enforceDeadline := ContextWithOptionalDeadline(ctx)
@@ -72,6 +74,7 @@ func TestContextWithOptionalDeadlineNegativeDeadline(t *testing.T) {
 }
 
 func TestContextWithOptionalDeadlineParentCancellation(t *testing.T) {
+	zreplcircleci.SkipOnCircleCI(t, "test relies on predictably low scheduler latency")
 
 	pctx, cancel := context.WithCancel(context.Background())
 	cctx, enforceDeadline := ContextWithOptionalDeadline(pctx)