A typical guaranteed delivery scenario covered as an
Enterprise Integration ensures the delivery of a message to a given backend
endpoint. As per this pattern the ESB would attempt to delivers the message to
the backend endpoint and if it fails, the message would be stored and delivered
once the backend endpoint becomes available. If the above guaranteed delivery mechanism
is implemented to a message flow that is synchronous the client would be
waiting for a response from the ESB until the message times out. To accommodate
synchronous clients in a guaranteed delivery scenario, it is possible for the
ESB to respond to the client with a fault message in case the message is not
delivered and stored for later delivery. The following diagram depicts the
message flow of the guaranteed delivery scenario with client acknowledgement
using the WSO2 ESB.
1.
Client sends the message to the ESB.
2.
ESB try to deliver the message to the backend system,
and the message fails
3.
ESB stores the message in a message queue
4.
ESB sends a response back to the client
(response can be customized as required)
5.
ESB picks the message from the queue and try to
deliver the message to the backend system; ESB retry can be customized to retry
a given number of attempts.
The following synapse configuration can be used to configure
this scenario. The configuration includes a proxy service, message broker,
message processor, sequences and endpoints required to create the required
mediation flow. Please note that the configuration is based on storing messages
in an ActiveMQ based message queue. Hence it is required to follow the steps mentioned
in the following link [1] setting up ActiveMQ with WSO2 ESB.
<proxy name="StockQuoteProxy"
transports="https http"
startOnLoad="true"
trace="disable">
<description/>
<target>
<inSequence>
<sequence key="delivery_seq"/>
</inSequence>
<outSequence>
<send/>
</outSequence>
</target>
<publishWSDL uri="file:repository/samples/resources/proxy/sample_proxy_1.wsdl"/>
</proxy>
<endpoint
name="queueEP">
<address
uri="http://localhost:9000/services/SimpleStockQuoteService"/>
</endpoint>
<endpoint
name="StockQuoteFO">
<address
uri="http://localhost:9000/services/SimpleStockQuoteService"</endpoint>
<sequence
name="delivery_seq" onError="errorHandler">
<enrich>
<source
type="envelope" clone="true"/>
<target
type="property" property="mssg"/>
</enrich>
<send>
<endpoint
key="StockQuoteFO"/>
</send>
</sequence>
<sequence
name="SendResponse">
<header
name="To" action="remove"/>
<property
name="RESPONSE" value="true"/>
<send/>
</sequence>
<sequence
name="errorHandler">
<makefault
version="soap11">
<code
xmlns:tns="http://www.w3.org/2003/05/soap-envelope"
value="tns:Receiver"/>
<reason
value="Message has been stored."/>
</makefault>
<clone>
<target
sequence="SendResponse"/>
<target
sequence="queueMessage"/>
</clone>
</sequence>
<sequence
name="queueMessage">
<enrich>
<source
type="property" clone="true" property="mssg"/>
<target
type="envelope"/>
</enrich>
<property
name="target.endpoint" value="queueEP"/>
<property
name="FORCE_SC_ACCEPTED" value="true"
scope="axis2"/>
<property
name="OUT_ONLY" value="true"/>
<store
messageStore="JMStore"/>
</sequence>
<messageStore
class="org.apache.synapse.message.store.impl.jms.JmsStore"
name="JMStore">
<parameter
name="java.naming.factory.initial">org.apache.activemq.jndi.ActiveMQInitialContextFactory</parameter>
<parameter
name="store.jms.cache.connection">false</parameter>
<parameter
name="java.naming.provider.url">tcp://localhost:61616</parameter>
<parameter
name="store.jms.JMSSpecVersion">1.1</parameter>
</messageStore>
<messageProcessor
class="org.apache.synapse.message.processor.impl.forwarder.ScheduledMessageForwardingProcessor"
name="ScheduledProcessor"
messageStore="JMStore">
<parameter
name="interval">20000</parameter>
<parameter
name="is.active">true</parameter>
</messageProcessor>
[1] https://docs.wso2.com/display/ESB481/Configure+with+ActiveMQ
