通过修改配置文件即可实现。
emq v1.1.3，rel\emqttd\etc\emqttd.config
‘subscription’扩展模块支持客户端上线时，自动订阅或恢复订阅某些主题(Topic):
%% Modules {modules, [ %% Client presence management module. %% Publish messages when client connected or disconnected {presence, [{qos, 0}]}, %% Subscribe topics automatically when client connected {subscription, [ %% $c will be replaced by clientid %% {"$queue/clients/$c", 1}, {"$c/w", 1} %% Static subscriptions from backend %%backend ]} %% Rewrite rules %% {rewrite, [{file, "etc/rewrite.config"}]} ]},
emq v2.3.11，软件架构做了调整，把功能集成在了emq_modules模块，/data/loaded_plugins默认会加载emq_modules。
我们只需要改动配置文件emqx-rel-2.3.11/deps/emq_modules/etc/emq_modules.conf
##-------------------------------------------------------------------- ## Subscription Module ##-------------------------------------------------------------------- ## Enable Subscription Module. ## ## Value: on | off module.subscription = on ## Subscribe the Topics automatically when client connected. module.subscription.1.topic = %c/w ## Qos of the subscription: 0 | 1 | 2 module.subscription.1.qos = 1 把module.subscription设置为on，
把module.subscription.1.topic设置为%c/w，%c是通配符，会自动切换成clientId。注意是%c，而不是$c。
