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<!DOCTYPE html> <html lang=en> <head> <meta charset=utf-8> <meta name=viewport content="width=device-width, initial-scale=1.0"> <meta name=description content=""> <meta name=author content=""> <title>Gossip Protocol - Serf</title> <link href="/stylesheets/bootstrap.min-82fe1490.css" media=screen rel=stylesheet /><link href="/stylesheets/main-e5014f86.css" media=screen rel=stylesheet /> <!--[if lt IE 9]><script src="/javascripts/html5shiv-310dd184.js"></script> <script src="/javascripts/respond.min-88c91176.js"></script><![endif]--> <script>
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</script> </head> <body class="page-Gossip Protocol"> <div id=header> <div class=container> <a class="navbar-brand logo" href="/"> <span></span> </a> <a class="navbar-brand text rls-l" href="/">SERF</a> <ul class="buttons nav navbar-nav navbar-right rls-sb"> <li class=first><a href="/downloads.html">Download</a></li> <li><a href="https://github.com/hashicorp/serf">Github</a></li> </ul> <ul class="main-links nav navbar-nav navbar-right rls-sb"> <li><a href="/intro/index.html">Intro</a></li> <li><a href="/docs/index.html">Docs</a></li> <li><a href="/community.html">Community</a></li> </ul> </div> </div> <div class=container> <div class=col-md-4> <div class="docs-sidebar hidden-print affix-top" role=complementary> <ul class="nav docs-sidenav"> <li> <a href="/docs/index.html">Documentation Home</a> </li> <li> <a href="/docs/upgrading.html">Upgrading and Compatibility</a> <ul class=nav> <li> <a href="/docs/upgrading.html">Upgrading Serf</a> </li> <li> <a href="/docs/compatibility.html">Compatibility Promise</a> </li> </ul> </li> <li class=active> <a href="/docs/internals/index.html">Serf Internals</a> <ul class=nav> <li class=active> <a href="/docs/internals/gossip.html">Gossip Protocol</a> </li> <li> <a href="/docs/internals/security.html">Security Model</a> </li> <li> <a href="/docs/internals/simulator.html">Convergence Simulator</a> </li> </ul> </li> <li> <a href="/docs/commands/index.html">Serf Commands (CLI)</a> <ul class=nav> <li> <a href="/docs/commands/agent.html">agent</a> </li> <li> <a href="/docs/commands/event.html">event</a> </li> <li> <a href="/docs/commands/force-leave.html">force-leave</a> </li> <li> <a href="/docs/commands/join.html">join</a> </li> <li> <a href="/docs/commands/keygen.html">keygen</a> </li> <li> <a href="/docs/commands/leave.html">leave</a> </li> <li> <a href="/docs/commands/members.html">members</a> </li> <li> <a href="/docs/commands/monitor.html">monitor</a> </li> </ul> </li> <li> <a href="/docs/agent/basics.html">Serf Agent</a> <ul class=nav> <li> <a href="/docs/agent/basics.html">Running and Stopping</a> </li> <li> <a href="/docs/agent/options.html">Configuration</a> </li> <li> <a href="/docs/agent/event-handlers.html">Event Handlers</a> </li> <li> <a href="/docs/agent/encryption.html">Encryption</a> </li> <li> <a href="/docs/agent/rpc.html">RPC Protocol</a> </li> </ul> <li> <a href="/docs/roadmap.html">Roadmap</a> </li> </ul> </div> </div> <div class=col-md-8 role=main> <div class=bs-docs-section> <h1 id=toc_0>Gossip Protocol</h1> <p>Serf uses a <a href="#">gossip protocol</a> to broadcast messages to the cluster. This page documents the details of this internal protocol. The gossip protocol is based on <a href="//www.cs.cornell.edu/~asdas/research/dsn02-swim.pdf">&quot;SWIM: Scalable Weakly-consistent Infection-style Process Group Membership Protocol&quot;</a>, with a few minor adaptations, mostly to increase propagation speed and convergence rate.</p> <div class="alert alert-block alert-warning"> <strong>Advanced Topic!</strong> This page covers the technical details of the internals of Serf. You don't need to know these details to effectively operate and use Serf. These details are documented here for those who wish to learn about them without having to go spelunking through the source code. </div> <h2 id=toc_1>SWIM Protocol Overview</h2> <p>Serf begins by joining an existing cluster or starting a new cluster. If starting a new cluster, additional nodes are expected to join it. New nodes in an existing cluster must be given the address of at least one existing member in order to join the cluster. The new member does a full state sync with the existing member over TCP and begins gossiping its existence to the cluster.</p> <p>Gossip is done over UDP with a configurable but fixed fanout and interval. This ensures that network usage is constant with regards to number of nodes. Complete state exchanges with a random node are done periodically over TCP, but much less often than gossip messages. This increases the likelihood that the membership list converges properly since the full state is
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