code: public DockerRuleBuilder expose(String hostPort, String containerPort) {
          publishAllPorts = false;
          exposeBuilder.expose(hostPort, containerPort);
          return this;
      }
docs: Expose single container port to specified host port.
  By default all container port are exposed to randomly assigned free
  host ports. <b>Using manual expose disables this so user must
  expose all required ports by hand</b>.
  
  @param hostPort External host port, container internal port will be mapped to.
  @param containerPort Container port to map to host.