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| <div class='page-header'> |
| |
| <h1>MultiPulse (UDP) Discovery</h1> |
| </div> |
| </div> |
| </div> |
| <div class="row"> |
| |
| <div class="col-md-12"> |
| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>MultiPulse is an alternative multicast lookup that does not use a |
| regular heartbeat. Instead, servers listen for a multicast request |
| packet (a pulse) to which a response is then sent. Multicast network |
| traffic is effectively reduced to an absolute minimum.</p> |
| </div> |
| <div class="paragraph"> |
| <p>MultiPulse is only useful in network scenarios where both client and |
| server can be configured to send multicast UDP packets.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_server_configuration">Server Configuration</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>After you boot the server for the first time the default configuration |
| will create the file <code>conf/conf.d/multipulse.properties</code> containing:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-properties" data-lang="properties">server = org.apache.openejb.server.discovery.MulticastPulseAgent |
| bind = 239.255.2.3 |
| port = 6142 |
| disabled = true |
| group = default</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>You just need to enable the agent by setting <code>disabled = false</code>. It is |
| advisable to disable multicast in the <code>multicast.properties file</code>, or at |
| least to use a different bind address or port should you wish to use |
| both.</p> |
| </div> |
| <div class="paragraph"> |
| <p>All of the above settings except <code>server</code> can be modified as required. |
| The <code>port</code> and <code>bind</code> must be valid for general multicast/udp network |
| communication.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>group</code> setting can be changed to further group/cluster servers that |
| may use the same multicast channel. As shown below the client also has |
| an optional <code>group</code> setting which can be used to select an appropriate |
| server cluster from the multicast channel (See MultiPulse Client).</p> |
| </div> |
| <div class="paragraph"> |
| <p>The next step is to ensure that the advertised services are configured |
| for discovery. Edit the <code>ejbd.properties</code> file (and any other enabled |
| services such as http, etc.) and ensure that the <code>discovery</code> option is |
| set to a value that remote clients will be able to resolve.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-properties" data-lang="properties">server = org.apache.openejb.server.ejbd.EjbServer |
| bind = 0.0.0.0 |
| port = 4201 |
| disabled = false |
| threads = 20 |
| discovery = ejb:ejbd://{bind}:{port}</code></pre> |
| </div> |
| </div> |
| <div class="admonitionblock note"> |
| <table> |
| <tr> |
| <td class="icon"> |
| <i class="fa icon-note" title="Note"></i> |
| </td> |
| <td class="content"> |
| If either <code>0.0.0.0</code> (IPv4) or <code>[::]</code> (IPv6) wildcard bind |
| addresses are used then the server will actually broadcast all of it’s |
| known public hosts to clients. Clients will then cycle though and |
| attempt to connect to the provided hosts until successful. |
| </td> |
| </tr> |
| </table> |
| </div> |
| <div class="paragraph"> |
| <p>If <code>localhost</code> is used then only clients on the same physical machine |
| will actually 'see' the server response.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_multipulse_client">MultiPulse Client</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>The multipulse functionality is not just for servers to find each other |
| in a cluster, it can also be used for EJB clients to discover a server. |
| A special <code>multipulse://</code> URL can be used in the <code>InitialContext</code> |
| properties to signify that multipulse should be used to seed the |
| connection process. Such as:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">Properties p = new Properties(); |
| p.put(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.RemoteInitialContextFactory"); |
| p.put(Context.PROVIDER_URL, "multipulse://239.255.2.3:6142?group=default&timeout=250"); |
| InitialContext remoteContext = new InitialContext(p);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The URL has optional query parameters such as <code>schemes</code> and <code>group</code> and |
| <code>timeout</code> which allow you to zero in on a particular type of service of |
| a particular cluster group as well as set how long you are willing to |
| wait in the discovery process till finally giving up. The first matching |
| service that it sees "flowing" around on the UDP stream is the one it |
| picks and sticks to for that and subsequent requests, ensuring UDP is |
| only used when there are no other servers to talk to.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Note that EJB clients do not need to use multipulse to find a server. If |
| the client knows the URL of a server in the cluster, it may use it and |
| connect directly to that server, at which point that server will share |
| the full list of its peers.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_multicast_servers_with_tcp_clients">Multicast Servers with TCP Clients</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Note that clients do not need to use multipulse to communicate with |
| servers. Servers can use multicast to discover each other, but clients |
| are still free to connect to servers in the network using the server’s |
| TCP address.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">Properties p = new Properties(); |
| p.put(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.RemoteInitialContextFactory"); |
| p.put(Context.PROVIDER_URL, "ejbd://192.168.1.30:4201"); |
| InitialContext remoteContext = new InitialContext(p);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>When the client connects, the server will send the URLs of all the |
| servers in the group and failover will take place normally.</p> |
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