ted-ross commented on a change in pull request #532: DISPATCH-1381: Create
procedure for handling undeliverable messages
URL: https://github.com/apache/qpid-dispatch/pull/532#discussion_r303592407
##########
File path: docs/books/user-guide/routing.adoc
##########
@@ -551,6 +551,87 @@ autoLink {
For information about additional attributes, see
link:{qdrouterdConfManPageUrl}#_autolink[autoLink] in the `qdrouterd.conf` man
page.
--
+=== Handling Undeliverable Messages for an Address
+
+You handle undeliverable messages for an address by configuring _fallback
destinations_.
+A fallback destination is a queue on a broker that stores messages that are
not directly routable to any consumers.
+
+During normal message delivery,
+{RouterName} delivers messages to the consumers that are attached to the
router network.
+However, if no consumers are reachable,
+the messages are diverted to any fallback destinations that were configured
for the address.
+When a consumer reconnects and becomes reachable again,
+it receives the messages stored at the fallback destination.
+
+[NOTE]
+====
+{RouterName} does not preserve delivery order for messages stored at a
fallback destination. When a consumer reconnects, it will receive the stored
messages interleaved with any new messages sent by producers.
+====
+
+.Prerequisites
+
+* The router is connected to a broker.
++
+For more information, see xref:connecting-to-external-amqp-containers-router[].
+
+.Procedure
+
+This procedure enables fallback for an address
+and configures autolinks to connect to the broker queue
+that provides the fallback destination for the address.
+
+. Enable fallback destinations for the address.
++
+[options="nowrap",subs="+quotes"]
+----
+address {
+ prefix: my-address
+ enableFallback: yes
+}
+----
+
+. Add an _outgoing_ autolink to a queue on the broker.
++
+--
+For the address for which you enabled fallback,
+if messages are not routable to any consumers,
+the router will use this autolink to send the messages to a queue on the
broker.
+
+[options="nowrap",subs="+quotes"]
+----
+autoLink {
+ address: my-address.2
+ direction: out
+ connection: my-broker
+ fallback: yes
+}
+----
+--
+
+. If you want the router to send queued messages to attached consumers as soon
as they connect to the router network,
+add an _incoming_ autolink.
++
+--
+As soon as a consumer attaches to the router,
+it will receive the messages stored in the broker queue,
+along with any new messages sent by the producer.
+However, the original delivery order of the queued messages is not preserved;
the queued messages will be interleaved with the new messages.
+
+If you do not add the incoming autolink,
+the messages will be stored on the broker,
+but will not be automatically sent to consumers when they attach to the router.
Review comment:
I would delete "automatically" as it's not adding any valuable meaning.
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