@Override
  public Configuration getConf(Configuration sinkConf, String replicationClusterId)
    throws IOException {
    if (sourceClustersConfs.get(replicationClusterId) == null) {
      synchronized (this.sourceClustersConfs) {
        if (sourceClustersConfs.get(replicationClusterId) == null) {
          LOG.info("Loading source cluster FS client conf for cluster " + replicationClusterId);
          // Load only user provided client configurations.
          Configuration sourceClusterConf = new Configuration(false);

          String replicationConfDir = sinkConf.get(HConstants.REPLICATION_CONF_DIR);
          if (replicationConfDir == null) {
            LOG.debug(HConstants.REPLICATION_CONF_DIR + " is not configured.");
            URL resource = HBaseConfiguration.class.getClassLoader().getResource("hbase-site.xml");
            if (resource != null) {
              String path = resource.getPath();
              replicationConfDir = path.substring(0, path.lastIndexOf("/"));
            } else {
              replicationConfDir = System.getenv("HBASE_CONF_DIR");
            }
          }

          File confDir = new File(replicationConfDir, replicationClusterId);
          LOG.info("Loading source cluster " + replicationClusterId
            + " file system configurations from xml " + "files under directory " + confDir);
          String[] listofConfFiles = FileUtil.list(confDir);
          for (String confFile : listofConfFiles) {
            if (new File(confDir, confFile).isFile() && confFile.endsWith(XML)) {
              // Add all the user provided client conf files
              sourceClusterConf.addResource(new Path(confDir.getPath(), confFile));
            }
          }
          this.sourceClustersConfs.put(replicationClusterId, sourceClusterConf);
        }
      }
    }
    return this.sourceClustersConfs.get(replicationClusterId);
  }
This will load all the xml configuration files for the source cluster replication ID from user
configured replication configuration directory.
hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/DefaultSourceFSConfigurationProvider.java