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               <h1>Multipoint Recommendations</h1>
             </div>
           </div>
         </div>
         <div class="row">

             <div class="col-md-12">
                 <div id="preamble">
 <div class="sectionbody">
 <div class="paragraph">
 <p>As mentioned the <code>initialServers</code> is only used for bootstrapping the
 multipoint network. Once running, all servers will dynamically establish
 direct connections with each other and there is no single point of
 failure.</p>
 </div>
 <div class="paragraph">
 <p>However to ensure that the bootstrapping process can occur successfully,
 the <code>initialServers</code> property of the <code>conf/multipoint.properties</code> file
 must be set carefully and with a specific server start order in mind.
 Each server consults its <code>initialServers</code> list exactly once in the
 bootstrapping phase at startup, after that time connections are made
 dynamically.</p>
 </div>
 <div class="paragraph">
 <p>This means that at least one of the servers listed in <code>initialServers</code>
 must already be running when the server starts or the server might never
 become introduced and connected to all the other servers in the network.</p>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_failed_scenario_background">Failed scenario background</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>As an example of a failed scenario, imagine there are three servers;
 <code>server1</code>, <code>server2</code>, <code>server3</code>. They are setup only to point to the
 server in front of them making a chain:</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p>server1; <code>initialServers = server2</code></p>
 </li>
 <li>
 <p>server2; <code>initialServers = server3</code></p>
 </li>
 <li>
 <p>server3; <code>initialServers = <strong>&lt;blank&gt;</strong></code></p>
 </li>
 </ul>
 </div>
 <div class="paragraph">
 <p>Which is essentially <code>server1</code> &#8594; <code>server2</code> &#8594; <code>server3</code>. This scenario
 could work, but they servers would have to be started in exactly the
 opposite order:</p>
 </div>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p><code>server3</code> starts</p>
 </li>
 <li>
 <p><code>server2</code> starts</p>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p><em>static:</em> connect to <code>server3</code></p>
 </li>
 </ol>
 </div>
 </li>
 <li>
 <p><code>server1</code> starts</p>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p><em>static:</em> connect to <code>server2</code></p>
 </li>
 <li>
 <p><em>dynamic:</em> connect to <code>server3</code></p>
 </li>
 </ol>
 </div>
 </li>
 </ol>
 </div>
 <div class="paragraph">
 <p>At this point all servers would be fully connected. But the above setup
 is flawed and could easily fail. The first flaw is <code>server3</code> lists
 nothing in its <code>initialServers</code> list, so if it were restarted it would
 leave the multipoint network and not know how to get back in.</p>
 </div>
 <div class="paragraph">
 <p>The second flaw is if you started them in any other order, you would
 also not get a fully connected multipoint network. Say the servers were
 started in "front" order:</p>
 </div>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p><code>server1</code> starts</p>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p><em>static:</em> connect to <code>server2</code> - failed, <code>server2</code> not started.</p>
 </li>
 </ol>
 </div>
 </li>
 <li>
 <p><code>server2</code> starts</p>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p><em>static:</em> connect to <code>server3</code> - failed, <code>server3</code> not started.</p>
 </li>
 </ol>
 </div>
 </li>
 <li>
 <p><code>server3</code> starts</p>
 <div class="olist arabic">
 <ol class="arabic">
 <li>
 <p>no connection attempts, initialServers list is empty.</p>
 </li>
 </ol>
 </div>
 </li>
 </ol>
 </div>
 <div class="paragraph">
 <p>After startup completes, all servers will be completely isolated and
 failover will not work. The described setup is weaker than it needs to
 be. Listing just one server means the listed server is a potential point
 of weakness. As a matter of trivia, it is interesting to point out that
 you could bring a fourth server online temporarily that lists all three
 servers. Once it makes the introductions and all servers learn of each
 other, you could shut it down again.</p>
 </div>
 <div class="paragraph">
 <p>The above setup is easily fixable via better configuration. If <code>server3</code>
 listed both <code>server1</code> and <code>server2</code> in its initialServers list, rather
 than listing nothing at all, then all servers would fully discover each
 other regardless of startup order; assuming all three servers did
 eventually start.</p>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_bootstrapping_three_servers_or_less">Bootstrapping Three Servers or Less</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>In a three sever scenario, we recommend simply having all three servers
 list all three servers.</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p>server1/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1, server2, server3</code></p>
 </li>
 </ul>
 </div>
 </li>
 <li>
 <p>server2/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1, server2, server3</code></p>
 </li>
 </ul>
 </div>
 </li>
 <li>
 <p>server3/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1, server2, server3</code></p>
 </li>
 </ul>
 </div>
 </li>
 </ul>
 </div>
 <div class="paragraph">
 <p>There&#8217;s no harm to a server listing itself. It gives you one clean list
 to maintain and it will work even if you decide not to start one of the
 three servers.</p>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_bootstrapping_four_servers_or_more">Bootstrapping Four Servers or More</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>In a scenario of four or more, we recommend picking at least to servers
 and focus on always keeping at least one of them running. Lets refer to
 them as "root" servers for simplicity sake.</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p>server1/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server2</code></p>
 </li>
 </ul>
 </div>
 </li>
 <li>
 <p>server2/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1</code></p>
 </li>
 </ul>
 </div>
 </li>
 </ul>
 </div>
 <div class="paragraph">
 <p>Root <code>server1</code> would list root <code>server2</code> so they would always be linked
 to each other regardless of start order or if one of them went down.
 <code>Server1</code> could be shutdown and reconnect on startup to the full
 multipoint network through <code>server2</code>, and vice versa.</p>
 </div>
 <div class="paragraph">
 <p>All other servers would simply list the root servers (<code>server1</code>,
 <code>server2</code>) in their initialServers list.</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p>server3/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1, server2</code></p>
 </li>
 </ul>
 </div>
 </li>
 <li>
 <p>server4/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1, server2</code></p>
 </li>
 </ul>
 </div>
 </li>
 <li>
 <p>serverN/conf/multipoint.properties</p>
 <div class="ulist">
 <ul>
 <li>
 <p><code>initialServers = server1, server2</code></p>
 </li>
 </ul>
 </div>
 </li>
 </ul>
 </div>
 <div class="paragraph">
 <p>As long as at least one root server (<code>server1</code> or <code>server2</code>) was
 running, you can bring other servers on and offline at will and always
 have a fully connected graph.</p>
 </div>
 <div class="paragraph">
 <p>Of course all servers once running and connected will have a full list
 of all other servers in the network, so if at any time the "root"
 servers weren&#8217;t around to make initial introductions to new servers it
 would be no trouble. It&#8217;s possible to reconfigure new servers to point
 at any other server in the network as all servers will have the full
 list. So these "root" servers are no real point of failure in function,
 but only of convenience.</p>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_setting_initialservers_overrides">Setting initialServers overrides</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>Always remember that any property in a
 <code>conf/&lt;server-service&gt;.properties</code> file can be overridden on the command
 line or via system properties. So it is possible easily set the
 <code>initialServers</code> list in startup scripts.</p>
 </div>
 <div class="paragraph">
 <p>A bash example might look something like:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">!/bin/bash

 OPENEJB_HOME=/opt/openejb-3.1.3
 INITIAL_LIST=$(cat /some/shared/directory/our_initial_servers.txt)

 $OPENEJB_HOME/bin/openejb start -Dmultipoint.initialServers=$INITIAL_LIST</code></pre>
 </div>
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	<h1>Multipoint Recommendations</h1>
	</div>
	</div>
	</div>
	<div class="row">

	<div class="col-md-12">
	<div id="preamble">
	<div class="sectionbody">
	<div class="paragraph">
	<p>As mentioned the <code>initialServers</code> is only used for bootstrapping the
	multipoint network. Once running, all servers will dynamically establish
	direct connections with each other and there is no single point of
	failure.</p>
	</div>
	<div class="paragraph">
	<p>However to ensure that the bootstrapping process can occur successfully,
	the <code>initialServers</code> property of the <code>conf/multipoint.properties</code> file
	must be set carefully and with a specific server start order in mind.
	Each server consults its <code>initialServers</code> list exactly once in the
	bootstrapping phase at startup, after that time connections are made
	dynamically.</p>
	</div>
	<div class="paragraph">
	<p>This means that at least one of the servers listed in <code>initialServers</code>
	must already be running when the server starts or the server might never
	become introduced and connected to all the other servers in the network.</p>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_failed_scenario_background">Failed scenario background</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>As an example of a failed scenario, imagine there are three servers;
	<code>server1</code>, <code>server2</code>, <code>server3</code>. They are setup only to point to the
	server in front of them making a chain:</p>
	</div>
	<div class="ulist">
	<ul>
	<li>
	<p>server1; <code>initialServers = server2</code></p>
	</li>
	<li>
	<p>server2; <code>initialServers = server3</code></p>
	</li>
	<li>
	<p>server3; <code>initialServers = <strong><blank></strong></code></p>
	</li>
	</ul>
	</div>
	<div class="paragraph">
	<p>Which is essentially <code>server1</code> → <code>server2</code> → <code>server3</code>. This scenario
	could work, but they servers would have to be started in exactly the
	opposite order:</p>
	</div>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p><code>server3</code> starts</p>
	</li>
	<li>
	<p><code>server2</code> starts</p>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p><em>static:</em> connect to <code>server3</code></p>
	</li>
	</ol>
	</div>
	</li>
	<li>
	<p><code>server1</code> starts</p>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p><em>static:</em> connect to <code>server2</code></p>
	</li>
	<li>
	<p><em>dynamic:</em> connect to <code>server3</code></p>
	</li>
	</ol>
	</div>
	</li>
	</ol>
	</div>
	<div class="paragraph">
	<p>At this point all servers would be fully connected. But the above setup
	is flawed and could easily fail. The first flaw is <code>server3</code> lists
	nothing in its <code>initialServers</code> list, so if it were restarted it would
	leave the multipoint network and not know how to get back in.</p>
	</div>
	<div class="paragraph">
	<p>The second flaw is if you started them in any other order, you would
	also not get a fully connected multipoint network. Say the servers were
	started in "front" order:</p>
	</div>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p><code>server1</code> starts</p>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p><em>static:</em> connect to <code>server2</code> - failed, <code>server2</code> not started.</p>
	</li>
	</ol>
	</div>
	</li>
	<li>
	<p><code>server2</code> starts</p>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p><em>static:</em> connect to <code>server3</code> - failed, <code>server3</code> not started.</p>
	</li>
	</ol>
	</div>
	</li>
	<li>
	<p><code>server3</code> starts</p>
	<div class="olist arabic">
	<ol class="arabic">
	<li>
	<p>no connection attempts, initialServers list is empty.</p>
	</li>
	</ol>
	</div>
	</li>
	</ol>
	</div>
	<div class="paragraph">
	<p>After startup completes, all servers will be completely isolated and
	failover will not work. The described setup is weaker than it needs to
	be. Listing just one server means the listed server is a potential point
	of weakness. As a matter of trivia, it is interesting to point out that
	you could bring a fourth server online temporarily that lists all three
	servers. Once it makes the introductions and all servers learn of each
	other, you could shut it down again.</p>
	</div>
	<div class="paragraph">
	<p>The above setup is easily fixable via better configuration. If <code>server3</code>
	listed both <code>server1</code> and <code>server2</code> in its initialServers list, rather
	than listing nothing at all, then all servers would fully discover each
	other regardless of startup order; assuming all three servers did
	eventually start.</p>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_bootstrapping_three_servers_or_less">Bootstrapping Three Servers or Less</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>In a three sever scenario, we recommend simply having all three servers
	list all three servers.</p>
	</div>
	<div class="ulist">
	<ul>
	<li>
	<p>server1/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1, server2, server3</code></p>
	</li>
	</ul>
	</div>
	</li>
	<li>
	<p>server2/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1, server2, server3</code></p>
	</li>
	</ul>
	</div>
	</li>
	<li>
	<p>server3/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1, server2, server3</code></p>
	</li>
	</ul>
	</div>
	</li>
	</ul>
	</div>
	<div class="paragraph">
	<p>There’s no harm to a server listing itself. It gives you one clean list
	to maintain and it will work even if you decide not to start one of the
	three servers.</p>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_bootstrapping_four_servers_or_more">Bootstrapping Four Servers or More</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>In a scenario of four or more, we recommend picking at least to servers
	and focus on always keeping at least one of them running. Lets refer to
	them as "root" servers for simplicity sake.</p>
	</div>
	<div class="ulist">
	<ul>
	<li>
	<p>server1/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server2</code></p>
	</li>
	</ul>
	</div>
	</li>
	<li>
	<p>server2/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1</code></p>
	</li>
	</ul>
	</div>
	</li>
	</ul>
	</div>
	<div class="paragraph">
	<p>Root <code>server1</code> would list root <code>server2</code> so they would always be linked
	to each other regardless of start order or if one of them went down.
	<code>Server1</code> could be shutdown and reconnect on startup to the full
	multipoint network through <code>server2</code>, and vice versa.</p>
	</div>
	<div class="paragraph">
	<p>All other servers would simply list the root servers (<code>server1</code>,
	<code>server2</code>) in their initialServers list.</p>
	</div>
	<div class="ulist">
	<ul>
	<li>
	<p>server3/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1, server2</code></p>
	</li>
	</ul>
	</div>
	</li>
	<li>
	<p>server4/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1, server2</code></p>
	</li>
	</ul>
	</div>
	</li>
	<li>
	<p>serverN/conf/multipoint.properties</p>
	<div class="ulist">
	<ul>
	<li>
	<p><code>initialServers = server1, server2</code></p>
	</li>
	</ul>
	</div>
	</li>
	</ul>
	</div>
	<div class="paragraph">
	<p>As long as at least one root server (<code>server1</code> or <code>server2</code>) was
	running, you can bring other servers on and offline at will and always
	have a fully connected graph.</p>
	</div>
	<div class="paragraph">
	<p>Of course all servers once running and connected will have a full list
	of all other servers in the network, so if at any time the "root"
	servers weren’t around to make initial introductions to new servers it
	would be no trouble. It’s possible to reconfigure new servers to point
	at any other server in the network as all servers will have the full
	list. So these "root" servers are no real point of failure in function,
	but only of convenience.</p>
	</div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_setting_initialservers_overrides">Setting initialServers overrides</h2>
	<div class="sectionbody">
	<div class="paragraph">
	<p>Always remember that any property in a
	<code>conf/<server-service>.properties</code> file can be overridden on the command
	line or via system properties. So it is possible easily set the
	<code>initialServers</code> list in startup scripts.</p>
	</div>
	<div class="paragraph">
	<p>A bash example might look something like:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java">!/bin/bash

	OPENEJB_HOME=/opt/openejb-3.1.3
	INITIAL_LIST=$(cat /some/shared/directory/our_initial_servers.txt)

	$OPENEJB_HOME/bin/openejb start -Dmultipoint.initialServers=$INITIAL_LIST</code></pre>
	</div>
	</div>
	</div>
	</div>
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