Have you ever wondered what happened behind the scene when you execute
yarn rmadmin -refreshNodes

https://github.com/apache/hadoop/blob/trunk/hadoop-yarn-project/hadoop-yarn/bin/yarn

The above is the shell script that runs when you call the yarn command

rmadmin)
    CLASS='org.apache.hadoop.yarn.client.cli.RMAdminCLI'
    hadoop_debug "Append YARN_CLIENT_OPTS onto HADOOP_OPTS"
    HADOOP_OPTS="${HADOOP_OPTS} ${YARN_CLIENT_OPTS}"

As you can seen above, the shell script invokes the class org.apache.hadoop.yarn.client.cli.RMAdminCLI when we issue the command yarn rmadmin -refreshNodes

Here is the refreshNodes() method in the class org.apache.hadoop.yarn.client.cli.RMAdminCLI. It uses the ClientRMProxy to make RPC call to the ResourceManager refreshNodes() method.

private int refreshNodes() throws IOException, YarnException {
    // Refresh the nodes
    ResourceManagerAdministrationProtocol adminProtocol = createAdminProtocol();
    RefreshNodesRequest request = RefreshNodesRequest
        .newInstance(DecommissionType.NORMAL);
    adminProtocol.refreshNodes(request);
    return 0;
  }



 protected ResourceManagerAdministrationProtocol createAdminProtocol()
      throws IOException {
    // Get the current configuration
    final YarnConfiguration conf = new YarnConfiguration(getConf());
    return ClientRMProxy.createRMProxy(conf,
        ResourceManagerAdministrationProtocol.class);
  }