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[66]1<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tribes - The Tomcat Cluster Communication Module - Apache Tribes - Introduction</title><meta value="Filip Hanik" name="author"><meta value="fhanik@apache.org" name="email"></head><body vlink="#525D76" alink="#525D76" link="#525D76" text="#000000" bgcolor="#ffffff"><table cellspacing="0" width="100%" border="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img border="0" alt="Apache Tomcat" align="right" src="../images/tomcat.gif"></a></td><td><font face="arial,helvetica,sanserif"><h1>Apache Tomcat 6.0</h1></font></td><td><!--APACHE LOGO--><a href="http://www.apache.org/"><img border="0" alt="Apache Logo" align="right" src="../images/asf-logo.gif"></a></td></tr></table><table cellspacing="4" width="100%" border="0"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr size="1" noshade></td></tr><tr><!--LEFT SIDE NAVIGATION--><td nowrap="true" valign="top" width="20%"><p><strong>Links</strong></p><ul><li><a href="../index.html">Docs Home</a></li><li><a href="http://tomcat.apache.org/faq">FAQ</a></li></ul><p><strong>User Guide</strong></p><ul><li><a href="introduction.html">1) Introduction</a></li><li><a href="setup.html">2) Setup</a></li><li><a href="faq.html">3) FAQ</a></li></ul><p><strong>Reference</strong></p><ul><li><a href="RELEASE-NOTES.txt">Release Notes</a></li><li><a href="/api/index.html">JavaDoc</a></li></ul><p><strong>Apache Tribes Development</strong></p><ul><li><a href="membership.html">Membership</a></li><li><a href="transport.html">Transport</a></li><li><a href="interceptors.html">Interceptors</a></li><li><a href="status.html">Status</a></li><li><a href="developers.html">Developers</a></li></ul></td><!--RIGHT SIDE MAIN BODY--><td align="left" valign="top" width="80%"><table cellspacing="4" width="100%" border="0"><tr><td valign="top" align="left"><h1>Apache Tribes - The Tomcat Cluster Communication Module</h1><h2>Apache Tribes - Introduction</h2></td><td nowrap="true" valign="top" align="right"><small><a href="printer/tribes.html"><img alt="Printer Friendly Version" border="0" src="../images/printer.gif"><br>print-friendly<br>version
2                    </a></small></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Quick Start"><strong>Quick Start</strong></a></font></td></tr><tr><td><blockquote>
3
4  <p>Apache Tribes is a group or peer-to-peer communcation framework that enables you to easily connect
5     your remote objects to communicate with each other.
6  </p>
7  <ul>
8    <li>Import: <code>org.apache.catalina.tribes.Channel</code></li>
9    <li>Import: <code>org.apache.catalina.tribes.Member</code></li>
10    <li>Import: <code>org.apache.catalina.tribes.MembershipListener</code></li>
11    <li>Import: <code>org.apache.catalina.tribes.ChannelListener</code></li>
12    <li>Import: <code>org.apache.catalina.tribes.group.GroupChannel</code></li>
13    <li>Create a class that implements: <code>org.apache.catalina.tribes.ChannelListener</code></li>
14    <li>Create a class that implements: <code>org.apache.catalina.tribes.MembershipListener</code></li>
15    <li>Simple class to demonstrate how to send a message:
16      <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
17        //create a channel
18        Channel myChannel = new GroupChannel();
19
20        //create my listeners
21        ChannelListener msgListener = new MyMessageListener();
22        MembershipListener mbrListener = new MyMemberListener();
23
24        //attach the listeners to the channel
25        myChannel.addMembershipListener(mbrListener);
26        myChannel.addChannelListener(msgListener);
27
28        //start the channel
29        myChannel.start(Channel.DEFAULT);
30
31        //create a message to be sent, message must implement java.io.Serializable
32        //for performance reasons you probably want them to implement java.io.Externalizable
33        Serializable myMsg = new MyMessage();
34
35        //retrieve my current members
36        Member[] group = myChannel.getMembers();
37
38        //send the message
39        channel.send(group,myMsg,Channel.SEND_OPTIONS_DEFAULT);
40      </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td></tr></table></div>
41    </li>
42  </ul>
43  <p>
44      Simple yeah? There is a lot more to Tribes than we have shown, hopefully the docs will be able
45      to explain more to you. Remember, that we are always interested in suggestions, improvements, bug fixes
46      and anything that you think would help this project.
47  </p>
48  <p>
49      Note: Tribes is currently built for JDK1.5, you can run on JDK1.4 by a small modifications to locks used from the <code>java.util.concurrent</code> package.
50  </p>
51</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="What is Tribes"><strong>What is Tribes</strong></a></font></td></tr><tr><td><blockquote>
52  <p>
53    Tribes is a messaging framework with group communication abilities. Tribes allows you to send and receive
54    messages over a network, it also allows for dynamic discovery of other nodes in the network.<br>
55    And that is the short story, it really is as simple as that. What makes Tribes useful and unique will be
56    described in the section below.<br>
57  </p>
58  <p>
59    The Tribes module was started early 2006 and a small part of the code base comes from the clustering module
60    that has been existing since 2003 or 2004.
61    The current cluster implementation has several short comings and many work arounds were created due
62    to the complexity in group communication. Long story short, what should have been two modules a long time
63    ago, will be now. Tribes takes out the complexity of messaging from the replication module and becomes
64    a fully independent and highly flexible group communication module.<br>
65  </p>
66  <p>
67    In Tomcat the old <code>modules/cluster</code> has now become <code>modules/groupcom</code>(Tribes) and
68    <code>modules/ha</code> (replication). This will allow development to proceed and let the developers
69    focus on the issues they are actually working on rather than getting boggled down in details of a module
70    they are not interested in. The understanding is that both communication and replication are complex enough,
71    and when trying to develop them in the same module, well you know, it becomes a cluster :)<br>
72  </p>
73  <p>
74    Tribes allows for guaranteed messaging, and can be customized in many ways. Why is this important?<br>
75    Well, you as a developer want to know that the messages you are sending are reaching their destination.
76    More than that, if a message doesn't reach its destination, the application on top of Tribes will be notified
77    that the message was never sent, and what node it failed.
78  </p>
79
80</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Why another messaging framework"><strong>Why another messaging framework</strong></a></font></td></tr><tr><td><blockquote>
81  <p>
82    I am a big fan of reusing code and would never dream of developing something if someone else has already
83    done it and it was available to me and the community I try to serve.<br>
84    When I did my research to improve the clustering module I was constantly faced with a few obstacles:<br>
85    1. The framework wasn't flexible enough<br>
86    2. The framework was licensed in a way that neither I nor the community could use it<br>
87    3. Several features that I needed were missing<br>
88    4. Messaging was guaranteed, but no feedback was reported to me<br>
89    5. The semantics of my message delivery had to be configured before runtime<br>
90    And the list continues...
91  </p>
92  <p>
93    So I came up with Tribes, to address these issues and other issues that came along.
94    When designing Tribes I wanted to make sure I didn't lose any of the flexibility and
95    delivery semantics that the existing frameworks already delivered. The goal was to create a framework
96    that could do everything that the others already did, but to provide more flexibility for the application
97    developer. In the next section will give you the high level overview of what features tribes offers or will offer.
98  </p>
99</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Feature Overview"><strong>Feature Overview</strong></a></font></td></tr><tr><td><blockquote>
100  <p>
101    To give you an idea of the feature set I will list it out here.
102    Some of the features are not yet completed, if that is the case they are marked accordingly.
103  </p>
104  <p>
105    <b>Pluggable modules</b><br>
106    Tribes is built using interfaces. Any of the modules or components that are part of Tribes can be swapped out
107    to customize your own Tribes implementation.
108  </p>
109  <p>
110    <b>Guaranteed Messaging</b><br>
111    In the default implementation of Tribes uses TCP for messaging. TCP already has guaranteed message delivery
112    and flow control built in. I believe that the performance of Java TCP, will outperform an implementation of
113    Java/UDP/flow-control/message guarantee since the logic happens further down the stack.<br>
114    Tribes supports both non-blocking and blocking IO operations. The recommended setting is to use non blocking
115    as it promotes better parallelism when sending and receiving messages. The blocking implementation is available
116    for those platforms where NIO is still a trouble child.
117  </p>
118  <p>
119    <b>Different Guarantee Levels</b><br>
120    There are three different levels of delivery guarantee when a message is sent.<br>
121    <ol>
122      <li>IO Based send guarantee. - fastest, least reliable<br>
123          This means that Tribes considers the message transfer to be successful
124          if the message was sent to the socket send buffer and accepted.<br>
125          On blocking IO, this would be <code>socket.getOutputStream().write(msg)</code><br>
126          On non blocking IO, this would be <code>socketChannel.write()</code>, and the buffer byte buffer gets emptied
127          followed by a <code>socketChannel.read()</code> to ensure the channel still open.
128          The <code>read()</code> has been added since <code>write()</code> will succeed if the connection has been "closed"
129          when using NIO.
130      </li>
131      <li>ACK based. - recommended, guaranteed delivery<br>
132          When the message has been received on a remote node, an ACK is sent back to the sender,
133          indicating that the message was received successfully.
134      </li>
135      <li>SYNC_ACK based. - guaranteed delivery, guaranteed processed, slowest<br>
136          When the message has been received on a remote node, the node will process
137          the message and if the message was processed successfully, an ACK is sent back to the sender
138          indicating that the message was received and processed successfully.
139          If the message was received, but processing it failed, an ACK_FAIL will be sent back
140          to the sender. This is a unique feature that adds an incredible amount value to the application
141          developer. Most frameworks here will tell you that the message was delivered, and the application
142          developer has to build in logic on whether the message was actually processed properly by the application
143          on the remote node. If configured, Tribes will throw an exception when it receives an ACK_FAIL
144          and associate that exception with the member that didn't process the message.
145      </li>
146    </ol>
147    You can of course write even more sophisticated guarantee levels, and some of them will be mentioned later on
148    in the documentation. One mentionable level would be a 2-Phase-Commit, where the remote applications don't receive
149    the message until all nodes have received the message. Sort of like a all-or-nothing protocol.
150  </p>
151  <p>
152    <b>Per Message Delivery Attributes</b><br>
153    Perhaps the feature that makes Tribes stand out from the crowd of group communication frameworks.
154    Tribes enables you to send to decide what delivery semantics a message transfer should have on a per
155    message basis. Meaning, that your messages are not delivered based on some static configuration
156    that remains fixed after the message framework has been started.<br>
157    To give you an example of how powerful this feature is, I'll try to illustrate it with a simple example.
158    Imagine you need to send 10 different messsages, you could send the the following way:
159    <div align="left"><table border="0" cellpadding="0" cellspacing="4"><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td></tr><tr><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" bgcolor="#ffffff"><pre>
160      Message_1 - asynchronous and fast, no guarantee required, fire and forget
161      Message_2 - all-or-nothing, either all receivers get it, or none.
162      Message_3 - encrypted and SYNC_ACK based
163      Message_4 - asynchronous, SYNC_ACK and call back when the message is processed on the remote nodes
164      Message_5 - totally ordered, this message should be received in the same order on all nodes that have been
165                  send totally ordered
166      Message_6 - asynchronous and totally ordered
167      Message_7 - RPC message, send a message, wait for all remote nodes to reply before returning
168      Message_8 - RPC message, wait for the first reply
169      Message_9 - RPC message, asynchronous, don't wait for a reply, collect them via a callback
170      Message_10- sent to a member that is not part of this group
171    </pre></td><td width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td></tr><tr><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td><td height="1" width="1" bgcolor="#023264"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../images/void.gif"></td></tr></table></div>
172    As you can imagine by now, these are just examples. The number of different semantics you can apply on a
173    per-message-basis is almost limitless. Tribes allows you to set up to 28 different on a message
174    and then configure Tribes to what flag results in what action on the message.<br>
175    Imagine a shared transactional cache, probably &gt;90% are reads, and the dirty reads should be completely
176    unordered and delivered as fast as possible. But transactional writes on the other hand, have to
177    be ordered so that no cache gets corrupted. With tribes you would send the write messages totally ordered,
178    while the read messages you simple fire to achieve highest throughput.<br>
179    There are probably better examples on how this powerful feature can be used, so use your imagination and
180    your experience to think of how this could benefit you in your application.
181  </p>
182  <p>
183    <b>Interceptor based message processing</b><br>
184    Tribes uses a customizable interceptor stack to process messages that are sent and received.<br>
185    <i>So what, all frameworks have this!</i><br>
186    Yes, but in Tribes interceptors can react to a message based on the per-message-attributes
187    that are sent runtime. Meaning, that if you add a encryption interceptor that encrypts message
188    you can decide if this interceptor will encrypt all messages, or only certain messages that are decided
189    by the applications running on top of Tribes.<br>
190    This is how Tribes is able to send some messages totally ordered and others fire and forget style
191    like the example above.<br>
192    The number of interceptors that are available will keep growing, and we would appreciate any contributions
193    that you might have.
194  </p>
195  <p>
196    <b>Threadless Interceptor stack</b>
197    The interceptor don't require any separate threads to perform their message manipulation.<br>
198    Messages that are sent will piggy back on the thread that is sending them all the way through transmission.
199    The exception is the <code>MessageDispatchInterceptor</code> that will queue up the message
200    and send it on a separate thread for asynchronous message delivery.
201    Messages received are controlled by a thread pool in the <code>receiver</code> component.<br>
202    The channel object can send a <code>heartbeat()</code> through the interceptor stack to allow
203    for timeouts, cleanup and other events.<br>
204    The <code>MessageDispatchInterceptor</code> is the only interceptor that is configured by default.
205  </p>
206  <p>
207    <b>Parallel Delivery</b><br>
208    Tribes support parallel delivery of messages. Meaning that node_A could send three messages to node_B in
209    parallel. This feature becomes useful when sending messages with different delivery semantics.
210    Otherwise if Message_1 was sent totally ordered, Message_2 would have to wait for that message to complete.<br>
211    Through NIO, Tribes is also able to send a message to several receivers at the same time on the same thread.
212  </p>
213  <p>
214    <b>Silent Member Messaging</b><br>
215    With Tribes you are able to send messages to members that are not in your group.
216    So by default, you can already send messages over a wide area network, even though the dynamic discover
217    module today is limited to local area networks by using multicast for dynamic node discovery.
218    Of course, the membership component will be expanded to support WAN memberships in the future.
219    But this is very useful, when you want to hide members from the rest of the group and only communicate with them
220  </p>
221</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Where can I get Tribes"><strong>Where can I get Tribes</strong></a></font></td></tr><tr><td><blockquote>
222  <p>
223   
224  </p>
225
226
227</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr size="1" noshade></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font size="-1" color="#525D76"><em>
228        Copyright &copy; 1999-2008, Apache Software Foundation
229        </em></font></div></td></tr></table></body></html>
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