/usr/share/tomcat6-docs/docs/tribes/introduction.html is in tomcat6-docs 6.0.39-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 | <html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Apache Tribes - The Tomcat Cluster Communication Module (6.0.39) - Apache Tribes - Introduction</title><meta name="author" content="Filip Hanik"><style type="text/css" media="print">
.noPrint {display: none;}
td#mainBody {width: 100%;}
</style></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img src="../images/tomcat.gif" align="right" alt="Apache Tomcat" border="0"></a></td><td><h1><font face="arial,helvetica,sanserif">Apache Tomcat 6.0</font></h1><font face="arial,helvetica,sanserif">Version 6.0.39, Feb 24 2014</font></td><td><!--APACHE LOGO--><a href="http://www.apache.org/"><img src="../images/asf-logo.gif" align="right" alt="Apache Logo" border="0"></a></td></tr></table><table border="0" width="100%" cellspacing="4"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr noshade size="1"></td></tr><tr><!--LEFT SIDE NAVIGATION--><td width="20%" valign="top" nowrap class="noPrint"><p><strong>Links</strong></p><ul><li><a href="../index.html">Docs Home</a></li><li><a href="http://wiki.apache.org/tomcat/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="../api/org/apache/catalina/tribes/package-summary.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 width="80%" valign="top" align="left" id="mainBody"><h1>Apache Tribes - The Tomcat Cluster Communication Module</h1><h2>Apache Tribes - Introduction</h2><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Table of Contents"><!--()--></a><a name="Table_of_Contents"><strong>Table of Contents</strong></a></font></td></tr><tr><td><blockquote>
<ul><li><a href="#Quick_Start">Quick Start</a></li><li><a href="#What_is_Tribes">What is Tribes</a></li><li><a href="#Why_another_messaging_framework">Why another messaging framework</a></li><li><a href="#Feature_Overview">Feature Overview</a></li><li><a href="#Where_can_I_get_Tribes">Where can I get Tribes</a></li></ul>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Quick Start"><!--()--></a><a name="Quick_Start"><strong>Quick Start</strong></a></font></td></tr><tr><td><blockquote>
<p>Apache Tribes is a group or peer-to-peer communication framework that enables you to easily connect
your remote objects to communicate with each other.
</p>
<ul>
<li>Import: <code>org.apache.catalina.tribes.Channel</code></li>
<li>Import: <code>org.apache.catalina.tribes.Member</code></li>
<li>Import: <code>org.apache.catalina.tribes.MembershipListener</code></li>
<li>Import: <code>org.apache.catalina.tribes.ChannelListener</code></li>
<li>Import: <code>org.apache.catalina.tribes.group.GroupChannel</code></li>
<li>Create a class that implements: <code>org.apache.catalina.tribes.ChannelListener</code></li>
<li>Create a class that implements: <code>org.apache.catalina.tribes.MembershipListener</code></li>
<li>Simple class to demonstrate how to send a message:
<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
//create a channel
Channel myChannel = new GroupChannel();
//create my listeners
ChannelListener msgListener = new MyMessageListener();
MembershipListener mbrListener = new MyMemberListener();
//attach the listeners to the channel
myChannel.addMembershipListener(mbrListener);
myChannel.addChannelListener(msgListener);
//start the channel
myChannel.start(Channel.DEFAULT);
//create a message to be sent, message must implement java.io.Serializable
//for performance reasons you probably want them to implement java.io.Externalizable
Serializable myMsg = new MyMessage();
//retrieve my current members
Member[] group = myChannel.getMembers();
//send the message
channel.send(group,myMsg,Channel.SEND_OPTIONS_DEFAULT);
</pre></td><td bgcolor="#023264" width="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
</li>
</ul>
<p>
Simple yeah? There is a lot more to Tribes than we have shown, hopefully the docs will be able
to explain more to you. Remember, that we are always interested in suggestions, improvements, bug fixes
and anything that you think would help this project.
</p>
<p>
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.
</p>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="What is Tribes"><!--()--></a><a name="What_is_Tribes"><strong>What is Tribes</strong></a></font></td></tr><tr><td><blockquote>
<p>
Tribes is a messaging framework with group communication abilities. Tribes allows you to send and receive
messages over a network, it also allows for dynamic discovery of other nodes in the network.<br>
And that is the short story, it really is as simple as that. What makes Tribes useful and unique will be
described in the section below.<br>
</p>
<p>
The Tribes module was started early 2006 and a small part of the code base comes from the clustering module
that has been existing since 2003 or 2004.
The current cluster implementation has several short comings and many workarounds were created due
to the complexity in group communication. Long story short, what should have been two modules a long time
ago, will be now. Tribes takes out the complexity of messaging from the replication module and becomes
a fully independent and highly flexible group communication module.<br>
</p>
<p>
In Tomcat the old <code>modules/cluster</code> has now become <code>modules/groupcom</code>(Tribes) and
<code>modules/ha</code> (replication). This will allow development to proceed and let the developers
focus on the issues they are actually working on rather than getting boggled down in details of a module
they are not interested in. The understanding is that both communication and replication are complex enough,
and when trying to develop them in the same module, well you know, it becomes a cluster :)<br>
</p>
<p>
Tribes allows for guaranteed messaging, and can be customized in many ways. Why is this important?<br>
Well, you as a developer want to know that the messages you are sending are reaching their destination.
More than that, if a message doesn't reach its destination, the application on top of Tribes will be notified
that the message was never sent, and what node it failed.
</p>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Why another messaging framework"><!--()--></a><a name="Why_another_messaging_framework"><strong>Why another messaging framework</strong></a></font></td></tr><tr><td><blockquote>
<p>
I am a big fan of reusing code and would never dream of developing something if someone else has already
done it and it was available to me and the community I try to serve.<br>
When I did my research to improve the clustering module I was constantly faced with a few obstacles:<br>
1. The framework wasn't flexible enough<br>
2. The framework was licensed in a way that neither I nor the community could use it<br>
3. Several features that I needed were missing<br>
4. Messaging was guaranteed, but no feedback was reported to me<br>
5. The semantics of my message delivery had to be configured before runtime<br>
And the list continues...
</p>
<p>
So I came up with Tribes, to address these issues and other issues that came along.
When designing Tribes I wanted to make sure I didn't lose any of the flexibility and
delivery semantics that the existing frameworks already delivered. The goal was to create a framework
that could do everything that the others already did, but to provide more flexibility for the application
developer. In the next section will give you the high level overview of what features tribes offers or will offer.
</p>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Feature Overview"><!--()--></a><a name="Feature_Overview"><strong>Feature Overview</strong></a></font></td></tr><tr><td><blockquote>
<p>
To give you an idea of the feature set I will list it out here.
Some of the features are not yet completed, if that is the case they are marked accordingly.
</p>
<p>
<b>Pluggable modules</b><br>
Tribes is built using interfaces. Any of the modules or components that are part of Tribes can be swapped out
to customize your own Tribes implementation.
</p>
<p>
<b>Guaranteed Messaging</b><br>
In the default implementation of Tribes uses TCP for messaging. TCP already has guaranteed message delivery
and flow control built in. I believe that the performance of Java TCP, will outperform an implementation of
Java/UDP/flow-control/message guarantee since the logic happens further down the stack.<br>
Tribes supports both non-blocking and blocking IO operations. The recommended setting is to use non blocking
as it promotes better parallelism when sending and receiving messages. The blocking implementation is available
for those platforms where NIO is still a trouble child.
</p>
<p>
<b>Different Guarantee Levels</b><br>
There are three different levels of delivery guarantee when a message is sent.<br>
<ol>
<li>IO Based send guarantee. - fastest, least reliable<br>
This means that Tribes considers the message transfer to be successful
if the message was sent to the socket send buffer and accepted.<br>
On blocking IO, this would be <code>socket.getOutputStream().write(msg)</code><br>
On non blocking IO, this would be <code>socketChannel.write()</code>, and the buffer byte buffer gets emptied
followed by a <code>socketChannel.read()</code> to ensure the channel still open.
The <code>read()</code> has been added since <code>write()</code> will succeed if the connection has been "closed"
when using NIO.
</li>
<li>ACK based. - recommended, guaranteed delivery<br>
When the message has been received on a remote node, an ACK is sent back to the sender,
indicating that the message was received successfully.
</li>
<li>SYNC_ACK based. - guaranteed delivery, guaranteed processed, slowest<br>
When the message has been received on a remote node, the node will process
the message and if the message was processed successfully, an ACK is sent back to the sender
indicating that the message was received and processed successfully.
If the message was received, but processing it failed, an ACK_FAIL will be sent back
to the sender. This is a unique feature that adds an incredible amount value to the application
developer. Most frameworks here will tell you that the message was delivered, and the application
developer has to build in logic on whether the message was actually processed properly by the application
on the remote node. If configured, Tribes will throw an exception when it receives an ACK_FAIL
and associate that exception with the member that didn't process the message.
</li>
</ol>
You can of course write even more sophisticated guarantee levels, and some of them will be mentioned later on
in the documentation. One mentionable level would be a 2-Phase-Commit, where the remote applications don't receive
the message until all nodes have received the message. Sort of like a all-or-nothing protocol.
</p>
<p>
<b>Per Message Delivery Attributes</b><br>
Perhaps the feature that makes Tribes stand out from the crowd of group communication frameworks.
Tribes enables you to send to decide what delivery semantics a message transfer should have on a per
message basis. Meaning, that your messages are not delivered based on some static configuration
that remains fixed after the message framework has been started.<br>
To give you an example of how powerful this feature is, I'll try to illustrate it with a simple example.
Imagine you need to send 10 different messages, you could send the the following way:
<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
Message_1 - asynchronous and fast, no guarantee required, fire and forget
Message_2 - all-or-nothing, either all receivers get it, or none.
Message_3 - encrypted and SYNC_ACK based
Message_4 - asynchronous, SYNC_ACK and call back when the message is processed on the remote nodes
Message_5 - totally ordered, this message should be received in the same order on all nodes that have been
send totally ordered
Message_6 - asynchronous and totally ordered
Message_7 - RPC message, send a message, wait for all remote nodes to reply before returning
Message_8 - RPC message, wait for the first reply
Message_9 - RPC message, asynchronous, don't wait for a reply, collect them via a callback
Message_10- sent to a member that is not part of this group
</pre></td><td bgcolor="#023264" width="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="../images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
As you can imagine by now, these are just examples. The number of different semantics you can apply on a
per-message-basis is almost limitless. Tribes allows you to set up to 28 different on a message
and then configure Tribes to what flag results in what action on the message.<br>
Imagine a shared transactional cache, probably >90% are reads, and the dirty reads should be completely
unordered and delivered as fast as possible. But transactional writes on the other hand, have to
be ordered so that no cache gets corrupted. With tribes you would send the write messages totally ordered,
while the read messages you simple fire to achieve highest throughput.<br>
There are probably better examples on how this powerful feature can be used, so use your imagination and
your experience to think of how this could benefit you in your application.
</p>
<p>
<b>Interceptor based message processing</b><br>
Tribes uses a customizable interceptor stack to process messages that are sent and received.<br>
<i>So what, all frameworks have this!</i><br>
Yes, but in Tribes interceptors can react to a message based on the per-message-attributes
that are sent runtime. Meaning, that if you add a encryption interceptor that encrypts message
you can decide if this interceptor will encrypt all messages, or only certain messages that are decided
by the applications running on top of Tribes.<br>
This is how Tribes is able to send some messages totally ordered and others fire and forget style
like the example above.<br>
The number of interceptors that are available will keep growing, and we would appreciate any contributions
that you might have.
</p>
<p>
<b>Threadless Interceptor stack</b>
The interceptor don't require any separate threads to perform their message manipulation.<br>
Messages that are sent will piggy back on the thread that is sending them all the way through transmission.
The exception is the <code>MessageDispatchInterceptor</code> that will queue up the message
and send it on a separate thread for asynchronous message delivery.
Messages received are controlled by a thread pool in the <code>receiver</code> component.<br>
The channel object can send a <code>heartbeat()</code> through the interceptor stack to allow
for timeouts, cleanup and other events.<br>
The <code>MessageDispatchInterceptor</code> is the only interceptor that is configured by default.
</p>
<p>
<b>Parallel Delivery</b><br>
Tribes support parallel delivery of messages. Meaning that node_A could send three messages to node_B in
parallel. This feature becomes useful when sending messages with different delivery semantics.
Otherwise if Message_1 was sent totally ordered, Message_2 would have to wait for that message to complete.<br>
Through NIO, Tribes is also able to send a message to several receivers at the same time on the same thread.
</p>
<p>
<b>Silent Member Messaging</b><br>
With Tribes you are able to send messages to members that are not in your group.
So by default, you can already send messages over a wide area network, even though the dynamic discover
module today is limited to local area networks by using multicast for dynamic node discovery.
Of course, the membership component will be expanded to support WAN memberships in the future.
But this is very useful, when you want to hide members from the rest of the group and only communicate with them
</p>
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Where can I get Tribes"><!--()--></a><a name="Where_can_I_get_Tribes"><strong>Where can I get Tribes</strong></a></font></td></tr><tr><td><blockquote>
<p>
Tribes ships as a module with Tomcat, and is released as part of the Apache Tomcat release.
</p>
</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr noshade size="1"></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font color="#525D76" size="-1"><em>
Copyright © 1999-2014, Apache Software Foundation
</em></font></div></td></tr></table></body></html>
|