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From kisho...@apache.org
Subject svn commit: r1420471 [5/6] - in /incubator/helix/site-content: ./ helix-admin-webapp/ helix-core/ images/ mockservice/ recipes/ recipes/rabbitmq-consumer-group/ recipes/rsync-replicated-file-system/
Date Tue, 11 Dec 2012 22:31:05 GMT
Added: incubator/helix/site-content/recipes/rabbitmq_consumer_group.html
URL: http://svn.apache.org/viewvc/incubator/helix/site-content/recipes/rabbitmq_consumer_group.html?rev=1420471&view=auto
==============================================================================
--- incubator/helix/site-content/recipes/rabbitmq_consumer_group.html (added)
+++ incubator/helix/site-content/recipes/rabbitmq_consumer_group.html Tue Dec 11 22:31:00
2012
@@ -0,0 +1,369 @@
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+        <div id="bodyColumn" >
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+            <!-- -
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License. --><h1>RabbitMQ Consumer Group</h1><p><a class="externalLink"
href="http://www.rabbitmq.com/">RabbitMQ</a> is a well known Open source software
the provides robust messaging for applications.</p><p>One of the commonly implemented
recipes using this software is a work queue. <a class="externalLink" href="http://www.rabbitmq.com/tutorials/tutorial-four-java.html">http://www.rabbitmq.com/tutorials/tutorial-four-java.html</a>
describes the use case where</p>
+<ul>
+  <li>A producer sends a message with a routing key.</li>
+  <li>The message goes to the queues whose binding key exactly matches the routing
key of the message.</li>
+  <li>There are multiple consumers and each consumer is interested in processing only
a subset of the messages by binding to the interested keys</li>
+</ul><p>The example provided <a class="externalLink" href="http://www.rabbitmq.com/tutorials/tutorial-four-java.html">here</a>
describes how multiple consumers can be started to process all the tasks.</p><p>While
this works, in production systems one needs the following * Ability to handle failures: when
a consumers fails another consumer must be started or the other consumers must start processing
these messages that should have been processed by the failed consumer. * When the existing
consumers cannot keep up with the task generation rate, new consumers will be added. The tasks
must be redistributed among all the consumers. </p><p>In this sample app, we explain
how these set of consumers can be grouped together and handle consumer failures and expansion
automatically.</p><p>Mapping this usecase to Helix is pretty easy as the binding
key/routing key is equivalent to a partition. </p><p>Lets take a real example.
Lets say a topic has 6 partitions, and we have 2 consumers to 
 process all the queues. What we want is all 6 queues to be evenly divided among 2 consumers.
Eventually when the system scales, we add more consumers to keep up. This will make each consumer
process tasks from 2 queues. Now lets say that a consumer fails and that the number of active
consumers is now reduced to 2. This means each consumer must process 3 queues.</p><p>We
showcase how such a dynamic App can be developed using Helix. </p><h1>Try it</h1><p>Before
getting into the details on how to develop such an App using Helix, you can try the following
steps to get a feel of it.</p>
+<div class="source"><pre class="prettyprint">git clone git@github.com:linkedin/helix.git
+cd helix
+./build
+export HELIX_PKG_ROOT=`pwd`/helix-core/target/helix-core-pkg
+</pre></div><p>OR Download the latest 0.5.28 release tar ball from <a
class="externalLink" href="http://linkedin.github.com/helix/download/release-0.5.28//helix-core-pkg-0.5.28.tar.gz">here</a>
<tt>
+tar -xzvf helix-core-pkg-0.5.28.tar.gz
+export HELIX_PKG_ROOT=`pwd`/helix-core-pkg
+</tt></p><p>Download the rabbitmq-consumer-group recipe from <a class="externalLink"
href="http://linkedin.github.com/helix/download/release-0.5.28/rabbitmq-consumer-group-0.5.28.tar.gz">here</a>
<tt>
+tar -xzvf rabbitmq-consumer-group-0.5.28.tar.gz
+export HELIX_RABBITMQ_ROOT=`pwd`/rabbitmq-consumer-group/
+</tt> <tt>
+chmod +x $HELIX_PKG_ROOT/bin/*
+chmod +x $HELIX_RABBITMQ_ROOT/bin/*
+</tt></p><div class="section"><h2>Install Rabbit MQ<a name="Install_Rabbit_MQ"></a></h2><p>Setting
up RabbitMQ on a local box is straightforward. You can find the instructions here <a class="externalLink"
href="http://www.rabbitmq.com/download.html">http://www.rabbitmq.com/download.html</a></p></div><div
class="section"><h2>Start ZK<a name="Start_ZK"></a></h2><p>Start
zookeeper at port 2199 <tt>
+$HELIX_PKG_ROOT/bin/start-standalone-zookeeper 2199
+</tt></p></div><div class="section"><h2>Setup the consumer
group cluster<a name="Setup_the_consumer_group_cluster"></a></h2><p>This
will setup the cluster by creating a rabbitmq-consumer-group cluster and adds a topic resource
with 6 queues. <tt>
+$HELIX_RABBITMQ_ROOT/bin/setup-cluster.sh localhost:2199 
+</tt></p></div><div class="section"><h2>Add consumers<a
name="Add_consumers"></a></h2><p>Start 2 consumers in 2 different terminals.
Each consumer is given a unique id. ``` //start-consumer.sh zookeeperAddress (e.g. localhost:2181)
consumerId , rabbitmqServer (e.g. localhost) $HELIX_RABBITMQ_ROOT/bin/start-consumer.sh localhost:2199
0 localhost $HELIX_RABBITMQ_ROOT/bin/start-consumer.sh localhost:2199 1 localhost </p>
+<div class="source"><pre class="prettyprint">Start HelixController
+--------------------
+Now start a Helix controller that starts managing the &quot;rabbitmq-consumer-group&quot;
cluster.
+</pre></div><p>$HELIX_RABBITMQ_ROOT/bin/start-cluster-manager.sh localhost:2199
```</p></div><div class="section"><h2>Send messages to the Topic<a
name="Send_messages_to_the_Topic"></a></h2><p>Start sending messages
to the topic. This script randomly selects a routing key (1-6) and sends the message to topic.
Based on the key, messages gets routed to the appropriate queue.</p>
+<div class="source"><pre class="prettyprint">$HELIX_RABBITMQ_ROOT/bin/send-message.sh
localhost 20
+</pre></div><p>After running this, you should see all 20 messages being
processed by 2 consumers. </p></div><div class="section"><h2>Add another
consumer<a name="Add_another_consumer"></a></h2><p>Once a new consumer
is started, helix detects it. In order to balance the load between 3 consumers, it deallocates
1 partition from the existing consumers and allocates it to the new consumer. We see that
each consumer is now processing only 2 queues. Helix makes sure that old nodes are asked to
stop consuming before the new consumer is asked to start consuming for a given partition.
But the transitions for each partition can happen in parallel. <tt>
+$HELIX_RABBITMQ_ROOT/bin/start-consumer.sh localhost:2199 2 localhost
+</tt></p><p>Send messages again to the topic. <tt>
+$HELIX_RABBITMQ_ROOT/bin/send-message.sh localhost 100
+</tt> You should see that messages are now received by all 3 consumers.</p></div><div
class="section"><h2>Stop a consumer<a name="Stop_a_consumer"></a></h2><p>In
any terminal press CTRL^C and notice that Helix detects the consumer failure and distributes
the 2 partitions that were processed by failed consumer to the remaining 2 active consumers.</p><h1>How
does it work</h1><p>Find the entire code <a class="externalLink" href="https://github.com/linkedin/helix/tree/master/recipes/rabbitmq-consumer-group/src/main/java/com/linkedin/helix/recipes/rabbitmq">here</a>.
</p></div><div class="section"><h2>Cluster setup<a name="Cluster_setup"></a></h2><p>This
step creates znode on zookeeper for the cluster and adds the state model. We use online offline
state model since there is no need for other states. The consumer is either processing a queue
or it is not.</p><p>It creates a resource called rabbitmq-consumer-group with
6 partitions. The execution mode is set to AUTO_REBALANCE. Thi
 s means that the Helix controls the assignment of partition to consumers and automatically
distributes the partitions evenly among the active consumers. When a consumer is added or
removed, it ensures that a minimum number of partitions are shuffled.</p>
+<div class="source"><pre class="prettyprint">      zkclient = new ZkClient(zkAddr,
ZkClient.DEFAULT_SESSION_TIMEOUT,
+          ZkClient.DEFAULT_CONNECTION_TIMEOUT, new ZNRecordSerializer());
+      ZKHelixAdmin admin = new ZKHelixAdmin(zkclient);
+      
+      // add cluster
+      admin.addCluster(clusterName, true);
+
+      // add state model definition
+      StateModelConfigGenerator generator = new StateModelConfigGenerator();
+      admin.addStateModelDef(clusterName, &quot;OnlineOffline&quot;,
+          new StateModelDefinition(generator.generateConfigForOnlineOffline()));
+
+      // add resource &quot;topic&quot; which has 6 partitions
+      String resourceName = &quot;rabbitmq-consumer-group&quot;;
+      admin.addResource(clusterName, resourceName, 6, &quot;OnlineOffline&quot;,
&quot;AUTO_REBALANCE&quot;);
+</pre></div></div><div class="section"><h2>Starting the consumers<a
name="Starting_the_consumers"></a></h2><p>The only thing consumers need
to know is the zkaddress, cluster name and consumer id. It does not need to know anything
else.</p>
+<div class="source"><pre class="prettyprint">   _manager =
+          HelixManagerFactory.getZKHelixManager(_clusterName,
+                                                _consumerId,
+                                                InstanceType.PARTICIPANT,
+                                                _zkAddr);
+
+      StateMachineEngine stateMach = _manager.getStateMachineEngine();
+      ConsumerStateModelFactory modelFactory =
+          new ConsumerStateModelFactory(_consumerId, _mqServer);
+      stateMach.registerStateModelFactory(&quot;OnlineOffline&quot;, modelFactory);
+
+      _manager.connect();
+
+</pre></div><p>Once the consumer has registered the statemodel and the
controller is started, the consumer starts getting callbacks (onBecomeOnlineFromOffline) for
the partition it needs to host. All it needs to do as part of the callback is to start consuming
messages from the appropriate queue. Similarly, when the controller deallocates a partitions
from a consumer, it fires onBecomeOfflineFromOnline for the same partition. As a part of this
transition, the consumer will stop consuming from a that queue.</p>
+<div class="source"><pre class="prettyprint"> @Transition(to = &quot;ONLINE&quot;,
from = &quot;OFFLINE&quot;)
+  public void onBecomeOnlineFromOffline(Message message, NotificationContext context)
+  {
+    LOG.debug(_consumerId + &quot; becomes ONLINE from OFFLINE for &quot; + _partition);
+
+    if (_thread == null)
+    {
+      LOG.debug(&quot;Starting ConsumerThread for &quot; + _partition + &quot;...&quot;);
+      _thread = new ConsumerThread(_partition, _mqServer, _consumerId);
+      _thread.start();
+      LOG.debug(&quot;Starting ConsumerThread for &quot; + _partition + &quot;
done&quot;);
+
+    }
+  }
+
+  @Transition(to = &quot;OFFLINE&quot;, from = &quot;ONLINE&quot;)
+  public void onBecomeOfflineFromOnline(Message message, NotificationContext context)
+      throws InterruptedException
+  {
+    LOG.debug(_consumerId + &quot; becomes OFFLINE from ONLINE for &quot; + _partition);
+
+    if (_thread != null)
+    {
+      LOG.debug(&quot;Stopping &quot; + _consumerId + &quot; for &quot; +
_partition + &quot;...&quot;);
+
+      _thread.interrupt();
+      _thread.join(2000);
+      _thread = null;
+      LOG.debug(&quot;Stopping &quot; +  _consumerId + &quot; for &quot;
+ _partition + &quot; done&quot;);
+
+    }
+  }
+</pre></div></div>
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