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+============
+Sync Modules
+============
+
+.. versionadded:: Kraken
+
+The `Multisite`_ functionality of RGW introduced in Jewel allowed the ability to
+create multiple zones and mirror data and metadata between them. ``Sync Modules``
+are built atop of the multisite framework that allows for forwarding data and
+metadata to a different external tier. A sync module allows for a set of actions
+to be performed whenever a change in data occurs (metadata ops like bucket or
+user creation etc. are also regarded as changes in data). As the rgw multisite
+changes are eventually consistent at remote sites, changes are propagated
+asynchronously. This would allow for unlocking use cases such as backing up the
+object storage to an external cloud cluster or a custom backup solution using
+tape drives, indexing metadata in ElasticSearch etc.
+
+A sync module configuration is local to a zone. The sync module determines
+whether the zone exports data or can only consume data that was modified in
+another zone. As of luminous the supported sync plugins are `elasticsearch`_,
+``rgw``, which is the default sync plugin that synchronises data between the
+zones and ``log`` which is a trivial sync plugin that logs the metadata
+operation that happens in the remote zones. The following docs are written with
+the example of a zone using `elasticsearch sync module`_, the process would be similar
+for configuring any sync plugin
+
+.. toctree::
+   :maxdepth: 1
+
+   ElasticSearch Sync Module <elastic-sync-module>
+   Cloud Sync Module <cloud-sync-module>
+   PubSub Module <pubsub-module>
+   Archive Sync Module <archive-sync-module>
+
+.. note ``rgw`` is the default sync plugin and there is no need to explicitly
+   configure this
+
+Requirements and Assumptions
+----------------------------
+
+Let us assume a simple multisite configuration as described in the `Multisite`_
+docs, of 2 zones ``us-east`` and ``us-west``, let's add a third zone
+``us-east-es`` which is a zone that only processes metadata from the other
+sites. This zone can be in the same or a different ceph cluster as ``us-east``.
+This zone would only consume metadata from other zones and RGWs in this zone
+will not serve any end user requests directly.
+
+
+Configuring Sync Modules
+------------------------
+
+Create the third zone similar to the `Multisite`_ docs, for example
+
+::
+
+   # radosgw-admin zone create --rgw-zonegroup=us --rgw-zone=us-east-es \
+   --access-key={system-key} --secret={secret} --endpoints=http://rgw-es:80
+
+
+
+A sync module can be configured for this zone via the following
+
+::
+
+   # radosgw-admin zone modify --rgw-zone={zone-name} --tier-type={tier-type} --tier-config={set of key=value pairs}
+
+
+For example in the ``elasticsearch`` sync module
+
+::
+
+   # radosgw-admin zone modify --rgw-zone={zone-name} --tier-type=elasticsearch \
+                               --tier-config=endpoint=http://localhost:9200,num_shards=10,num_replicas=1
+
+
+For the various supported tier-config options refer to the `elasticsearch sync module`_ docs
+
+Finally update the period
+
+
+::
+
+    # radosgw-admin period update --commit
+
+
+Now start the radosgw in the zone
+
+::
+
+    # systemctl start ceph-radosgw@rgw.`hostname -s`
+    # systemctl enable ceph-radosgw@rgw.`hostname -s`
+
+
+
+.. _`Multisite`: ../multisite
+.. _`elasticsearch sync module`: ../elastic-sync-module
+.. _`elasticsearch`: ../elastic-sync-module
+.. _`cloud sync module`: ../cloud-sync-module
+.. _`pubsub module`: ../pubsub-module
+.. _`archive sync module`: ../archive-sync-module