| <!DOCTYPE html> |
| <html lang="en"> |
| <head> |
| |
| <meta charset="UTF-8"> |
| <title>EJB Client/Server Failover</title> |
| <meta name="description" content="Apache TomEE"> |
| <meta name="author" content="Apache TomEE"> |
| <meta name="google-translate-customization" content="f36a520c08f4c9-0a04e86a9c075ce9-g265f3196f697cf8f-10"> |
| <meta http-equiv="Pragma" content="no-cache"> |
| <meta http-equiv="Expires" content="0"> |
| <meta http-equiv="Cache-Control" content="no-store, no-cache, must-revalidate, max-age=0"> |
| |
| <!-- Le HTML5 shim, for IE6-8 support of HTML elements --> |
| <!--[if lt IE 9]> |
| <script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script> |
| <![endif]--> |
| |
| <!-- Le styles --> |
| <link href="./resources/css/bootstrap.css" rel="stylesheet"> |
| <link href="./resources/css/prettify.css" rel="stylesheet"> |
| <!--link href="./resources/css/bootstrap-mods.css" rel="stylesheet"--> |
| <link href="./resources/css/main.css" rel="stylesheet"> |
| <link href="./resources/font-awesome-4.6.3/css/font-awesome.min.css" rel="stylesheet"> |
| |
| <script type="text/javascript"> |
| var t = encodeURIComponent(document.title.replace(/^\s+|\s+$/g,"")); |
| var u = encodeURIComponent(""+document.URL); |
| |
| function fbshare () { |
| window.open( |
| "http://www.facebook.com/sharer/sharer.php?u="+u, |
| 'Share on Facebook', |
| 'width=640,height=426'); |
| }; |
| function gpshare () { |
| window.open( |
| "https://plus.google.com/share?url="+u, |
| 'Share on Google+', |
| 'width=584,height=385'); |
| }; |
| function twshare () { |
| window.open( |
| "https://twitter.com/intent/tweet?url="+u+"&text="+t, |
| 'Share on Twitter', |
| 'width=800,height=526'); |
| }; |
| function pinshare () { |
| window.open("//www.pinterest.com/pin/create/button/?url="+u+"&media=http%3A%2F%2Ftomee.apache.org%2Fresources%2Fimages%2Ffeather-logo.png&description="+t, |
| 'Share on Pinterest', |
| 'width=800,height=526'); |
| }; |
| </script> |
| |
| <!-- Le fav and touch icons --> |
| <link rel="shortcut icon" href="./favicon.ico"> |
| <link rel="apple-touch-icon" href="./resources/images/apple-touch-icon.png"> |
| <link rel="apple-touch-icon" sizes="72x72" href="./resources/images/apple-touch-icon-72x72.png"> |
| <link rel="apple-touch-icon" sizes="114x114" href="./resources/images/apple-touch-icon-114x114.png"> |
| |
| <script src="./resources/js/prettify.js" type="text/javascript"></script> |
| <script src="./resources/js/jquery-latest.js"></script> |
| <script src="http://platform.twitter.com/widgets.js" type="text/javascript"></script> |
| <script src="./resources/js/common.js"></script> |
| <script src="./resources/js/prettyprint.js"></script> |
| <!--script src="//assets.pinterest.com/js/pinit.js" type="text/javascript" async></script//--> |
| |
| <script type="text/javascript"> |
| |
| var _gaq = _gaq || []; |
| _gaq.push(['_setAccount', 'UA-2717626-1']); |
| _gaq.push(['_setDomainName', 'apache.org']); |
| _gaq.push(['_trackPageview']); |
| |
| (function() { |
| var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; |
| ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; |
| var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); |
| })(); |
| |
| </script> |
| </head> |
| |
| <body> |
| |
| <div class="topbar" data-dropdown="dropdown"> |
| <div class="fill"> |
| <div class="container"> |
| <a class="brand" href="./index.html">Apache TomEE</a> |
| <ul class="nav"> |
| <li class="dropdown"> |
| <a class="dropdown-toggle" data-toggle="dropdown" href="#"> |
| Apache |
| <b class="caret"></b> |
| </a> |
| <ul class="dropdown-menu"> |
| <!-- <li><a href="./misc/whoweare.html">Who we are?</a></li> --> |
| <!-- <li><a href="./misc/heritage.html">Heritage</a></li> --> |
| <li><a href="http://www.apache.org">Apache Home</a></li> |
| <!-- <li><a href="./misc/resources.html">Resources</a></li> --> |
| <li><a href="./misc/contact.html">Contact</a></li> |
| <li><a href="./misc/legal.html">Legal</a></li> |
| <li><a href="http://www.apache.org/foundation/sponsorship.html">Sponsorship</a></li> |
| <li><a href="http://www.apache.org/foundation/thanks.html">Thanks</a></li> |
| <li class="divider"/> |
| <li><a href="http://www.apache.org/security">Security</a></li> |
| </ul> |
| </li> |
| <li><a href="./index.html">Home</a></li> |
| <li><a href="./downloads.html">Downloads</a></li> |
| <li><a href="./documentation.html">Documentation</a></li> |
| <li><a href="./examples-trunk/index.html">Examples</a></li> |
| <li><a href="./support.html">Support</a></li> |
| <li><a href="./contribute.html">Contribute</a></li> |
| <li><a href="./security/index.html">Security</a></li> |
| </ul> |
| |
| <!-- Google CSE Search Box Begins --> |
| <FORM class="pull-right" id="searchbox_010475492895890475512:_t4iqjrgx90" action="http://www.google.com/cse"> |
| <INPUT type="hidden" name="cx" value="010475492895890475512:_t4iqjrgx90"> |
| <INPUT type="hidden" name="cof" value="FORID:0"> |
| <INPUT size="18" width="130" style="width:130px" name="q" type="text" placeholder="Search"> |
| </FORM> |
| <!--<SCRIPT type="text/javascript" src="http://www.google.com/coop/cse/brand?form=searchbox_010475492895890475512:_t4iqjrgx90"></SCRIPT>--> |
| <!-- Google CSE Search Box Ends --> |
| </div> |
| </div> |
| </div> |
| |
| <div class="container"> |
| |
| |
| <div class="page-header"> |
| <small><a href="./index.html">Home</a></small><br> |
| <h1>EJB Client/Server Failover |
| |
| <div style="float: right; position: relative; bottom: -10px; "> |
| <a onclick="javascript:gpshare()" class="gp-share sprite" title="Share on Google+">share [gp]</a> |
| <a onclick="javascript:fbshare()" class="fb-share sprite" title="Share on Facebook">share [fb]</a> |
| <a onclick="javascript:twshare()" class="tw-share sprite" title="Share on Twitter">share [tw]</a> |
| <a onclick="javascript:pinshare()" class="pin-share sprite" title="Share on Pinterest">share [pin]</a> |
| <a data-toggle="modal" href="#edit" class="edit-page" title="Contribute to this Page">contribute</a> |
| </div> |
| </h1> |
| </div> |
| |
| <p>OpenEJB supports stateless failover. Specifically, the ability for an EJB |
| client to failover from one server to the next if a request cannot be |
| completed. No application state information is communicated between the |
| servers, so this functionality should be used only with applications that |
| are inherently stateless. A common term for this sort of setup is a server |
| farm.</p> |
| |
| <p>The basic design assumption is that all servers in the same group have the |
| same applications deployed and are capable of doing the same job. Servers |
| can be brought online and offline while clients are running. As members |
| join/leave this information is sent to the client as part of normal EJB |
| request/response communication so active clients always have the most |
| current information on servers that can process their request should |
| communication with a particular server fail.</p> |
| |
| <h1>Client Behavior</h1> |
| |
| <p>On each request to the server, the client will send the version number |
| associated with the list of servers in the cluster it is aware of. |
| Initially this version will be zero and the list will be empty. Only when |
| the server sees the client has an old list will the server send the updated |
| list. This is an important distinction as the list is not transmitted back |
| and forth on every request, only on change. If the membership of the |
| cluster is stable there is essentially no clustering overhead to the |
| protocol -- 8 byte overhead to each request and 1 byte on each response -- |
| so you will <em>not</em> see an exponential slowdown in response times the more |
| members are added to the cluster. This new list takes affect for all |
| proxies that share the same connection.</p> |
| |
| <p>When a server shuts down, more connections are refused, existing |
| connections not in mid-request are closed, any remaining connections are |
| closed immediately after completion of the request in progress and clients |
| can failover gracefully to the next server in the list. If a server |
| crashes requests are retried on the next server in the list (or depending |
| on the <code>ConnectionStrategy</code>). This failover pattern is followed until there |
| are no more servers in the list at which point the client attempts a final |
| multicast search (if it was created with a <code>PROVIDER_URL</code> starting with |
| <code>multicast://</code>) before abandoning the request and throwing an exception to |
| the caller.</p> |
| |
| <p>By default, the failover is ordered but random selection is supported. The |
| multicast discovery aspect of the client adds a nice randomness to the |
| selection of the first server.</p> |
| |
| <h1>Discovery</h1> |
| |
| <p>Each discoverable service has a URI which is broadcast as a heartbeat to |
| other servers in the cluster. This URI advertises the service's type, its |
| cluster group, and its location in the format of 'group:type:location'. |
| Say for example "cluster1:ejb:ejbd://thehost:4201". The URI is sent out |
| repeatedly in a pulse and its presence on the network indicates its |
| availability and its absence indicates the service is no longer available.</p> |
| |
| <p>The sending of this pulse (the heartbeat) can be done via UDP or TCP: |
| multicast and "multipoint" respectively. More on that in the following |
| section. The rate at which the heartbeat is pulsed to the network can be |
| specified via the 'heart_rate' property. The default is 500 milliseconds. |
| This rate is also used when listening for services on the network. If a |
| service goes missing for the duration of 'heart_rate' multiplied by |
| 'max_missed_heartbeats', then the service is considered dead.</p> |
| |
| <p>The 'group' property, cluster1 in the example, is used to dissect the |
| servers on the network into smaller logical clusters. A given server will |
| broadcast all it's services with the group prefixed in the URI, as well it |
| will ignore any services it sees broadcast if they do not share the same |
| group name.</p> |
| |
| <h1>Details</h1> |
| |
| <p>Multicast</p> |
| |
| <ul> |
| <li><a href="multicast-discovery.html">Multicast UDP Discovery</a></li> |
| <li><a href="multipulse-discovery.html">Multipulse UDP Discovery</a></li> |
| </ul> |
| |
| <p>Multipoint</p> |
| |
| <ul> |
| <li><a href="multipoint-discovery.html">Multipoint TCP Discovery</a></li> |
| <li><a href="multipoint-considerations.html">Considerations</a></li> |
| <li><a href="multipoint-recommendations.html">Recommendations</a></li> |
| </ul> |
| |
| <p>Logging</p> |
| |
| <ul> |
| <li><a href="failover-logging.html">Failover Logging Events</a></li> |
| </ul> |
| |
| |
| |
| |
| <div id="edit" class="modal hide fade in" style="display: none; "> |
| <div class="modal-header"> |
| <a class="close" data-dismiss="modal">x</a> |
| |
| <h3>Thank you for contributing to the documentation!</h3> |
| </div> |
| <div class="modal-body"> |
| <h4>Any help with the documentation is greatly appreciated.</h4> |
| <p>All edits are reviewed before going live, so feel free to do much more than fix typos or links. If you see a page that could benefit from an entire rewrite, we'd be thrilled to review it. Don't be surprised if we like it so much we ask you for help with other pages :)</p> |
| <small>NOTICE: unless indicated otherwise on the pages in question, all editable content available from apache.org is presumed to be licensed under the Apache License (AL) version 2.0 and hence all submissions to apache.org treated as formal Contributions under the license terms.</small> |
| <!--[if gt IE 6]> |
| <h4>Internet Explorer Users</h4> |
| <p>If you are not an Apache committer, click the Yes link and enter a <i>anonymous</i> for the username and leave the password empty</p> |
| <![endif]--> |
| |
| </div> |
| <div class="modal-footer"> |
| Do you have an Apache ID? |
| <a href="javascript:void(location.href='https://cms.apache.org/redirect?uri='+escape(location.href))" class="btn">Yes</a> |
| <a href="javascript:void(location.href='https://anonymous:@cms.apache.org/redirect?uri='+escape(location.href))" class="btn">No</a> |
| </div> |
| </div> |
| <script src="./resources/js/bootstrap-modal.js"></script> |
| |
| <footer> |
| <p>Copyright © 1999-2016 The Apache Software Foundation, Licensed under the Apache License, Version 2.0. |
| Apache TomEE, TomEE, Apache, the Apache feather logo, and the Apache TomEE project logo are trademarks of The Apache Software Foundation. |
| All other marks mentioned may be trademarks or registered trademarks of their respective owners.</p> |
| </footer> |
| |
| </div> <!-- /container --> |
| |
| <!-- Javascript |
| ================================================== --> |
| <!-- Placed at the end of the document so the pages load faster --> |
| <script src="./resources/js/bootstrap-dropdown.js"></script> |
| |
| </body> |
| </html> |