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操作步骤如下：
1. k8s环境下，consumer端开启mesh模式
2. consumer端需要调用多个provider
3. provider有应用级注册和接口级注册，并且需要的provider不再同一个namespace下
4. 原有项目存在dubbo2.6与3.1多版本间的相互调用，在开启消费端mesh（dubbo3.1）后，无法调用到2.6的服务提供者

**问题：**

1. 如何实现在一个consumer下，调用多个namespace下的provider，并且provider有应用级注册和接口级注册
2. dubbo3.1消费端在开启mesh后，如何调用版本是2.6的服务提供者
*/
    String SUBSCRIBED_SERVICE_NAMES_KEY = "subscribed-services";
    String PROVIDED_BY = "provided-by";
    /**
     * The provider tri port
     *
     * @since 3.1.0
     */
    String PROVIDER_PORT = "provider-port";
    /**
     * The request size of service instances
     *
     * @since 2.7.5
     */
    String INSTANCES_REQUEST_SIZE_KEY = "instances-request-size";
    /**
     * The default request size of service instances
     */
    int DEFAULT_INSTANCES_REQUEST_SIZE = 100;
    String ACCEPTS_KEY = "accepts";
    String REGISTRY_ZONE = "registry_zone";
    String REGISTRY_ZONE_FORCE = "registry_zone_force";
    String ZONE_KEY = "zone";
    String REGISTRY_SERVICE_REFERENCE_PATH = "org.apache.dubbo.registry.RegistryService";
    String INIT = "INIT";
    float DEFAULT_HASHMAP_LOAD_FACTOR = 0.75f;
    String ENABLE_EMPTY_PROTECTION_KEY = "enable-empty-protection";
    String REGISTER_CONSUMER_URL_KEY = "register-consumer-url";
}