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<div class="title">gRPC Name Resolution </div>  </div>
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<div class="textblock"><h2>Overview</h2>
<p>gRPC supports DNS as the default name-system. A number of alternative name-systems are used in various deployments. We support an API that is general enough to support a range of name-systems and the corresponding syntax for names. The gRPC client library in various languages will provide a plugin mechanism so resolvers for different name-systems can be plugged in.</p>
<h2>Detailed Design</h2>
<h3>Name Syntax</h3>
<p>A fully qualified, self contained name used for gRPC channel construction uses the syntax:</p>
<div class="fragment"><div class="line">scheme://authority/endpoint_name</div></div><!-- fragment --><p>Here, <code>scheme</code> indicates the name-system to be used. Currently, we support the following schemes:</p>
<ul>
<li><code>dns</code></li>
<li><code>ipv4</code> (IPv4 address)</li>
<li><code>ipv6</code> (IPv6 address)</li>
<li><code>unix</code> (path to unix domain socket &ndash; unix systems only)</li>
</ul>
<p>In the future, additional schemes such as <code>etcd</code> could be added.</p>
<p>The <code>authority</code> indicates some scheme-specific bootstrap information, e.g., for DNS, the authority may include the IP[:port] of the DNS server to use. Often, a DNS name may be used as the authority, since the ability to resolve DNS names is already built into all gRPC client libraries.</p>
<p>Finally, the <code>endpoint_name</code> indicates a concrete name to be looked up in a given name-system identified by the scheme and the authority. The syntax of the endpoint name is dictated by the scheme in use.</p>
<h3>Resolver Plugins</h3>
<p>The gRPC client library will use the specified scheme to pick the right resolver plugin and pass it the fully qualified name string.</p>
<p>Resolvers should be able to contact the authority and get a resolution that they return back to the gRPC client library. The returned contents include:</p>
<ul>
<li>A list of resolved addresses, each of which has three attributes:<ul>
<li>The address itself, including both IP address and port.</li>
<li>A boolean indicating whether the address is a backend address (i.e., the address to use to contact the server directly) or a balancer address (for cases where <a class="el" href="load-balancing_8md.html">external load balancing</a> is in use).</li>
<li>The name of the balancer, if the address is a balancer address. This will be used to perform peer authorization.</li>
</ul>
</li>
<li>A <a class="el" href="service__config_8md.html">service config</a>.</li>
</ul>
<p>The plugin API allows the resolvers to continuously watch an endpoint and return updated resolutions as needed. </p>
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