public synchronized MockServer getMockServer(String host, int port) {
    DataNodeId dataNodeId = clustermap.getDataNodeId(host, port);
    return mockServers.get(dataNodeId);
  }
Get the {@link MockServer} associated with the given host and port. Creates one if there is not any.
@param host the host
@param port the port
@return the {@link MockServer} associated with this host and port.
ambry-router/src/test/java/com/github/ambry/router/MockServerLayout.java