docs: document fan-out replication & add quick-start guide

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>
2021-12-31 18:39:49 -05:00
parent 1ad7df2df3
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+.. 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.