System Topic

EMQX periodically publishes its running status, message statistics, client online and offline events to the system topic starting with $SYS/.

The $SYS topic path begins with $SYS/brokers/{node}/, where {node} is the name of the node where the event/message is generated, for example:

$SYS/brokers/emqx@127.0.0.1/version
$SYS/brokers/emqx@127.0.0.1/uptime

$SYS system message publish interval is configured via Dashboard‘s Management/MQTT Setting/System Topic.

TIP

By default, only MQTT clients on localhost are allowed to subscribe to the $SYS topic. Please refer to File Authorization to modify the ACL rules for publish and subscribe.

Most of the data of the $SYS topic in EMQX can be obtained through other methods with lower Couplings. The device online and offline status can be captured and processed in the Rule Engine.

Cluster Status Information

Client Online and Offline Events

Those events is enabled by default, please refer to sys_topics.sys_event_messages to turn it off.

$SYS topic prefix: $SYS/brokers/${node}/clients/

The Payload of the connected event message can be parsed into JSON format:

{
    "username": "foo",
    "ts": 1625572213873,
    "sockport": 1883,
    "proto_ver": 4,
    "proto_name": "MQTT",
    "keepalive": 60,
    "ipaddress": "127.0.0.1",
    "expiry_interval": 0,
    "connected_at": 1625572213873,
    "connack": 0,
    "clientid": "emqtt-8348fe27a87976ad4db3",
    "clean_start": true
}

The Payload of the disconnected event message can be parsed into JSON format:

{
    "username": "foo",
    "ts": 1625572213873,
    "sockport": 1883,
    "reason": "tcp_closed",
    "proto_ver": 4,
    "proto_name": "MQTT",
    "ipaddress": "127.0.0.1",
    "disconnected_at": 1625572213873,
    "clientid": "emqtt-8348fe27a87976ad4db3"
}

Client Subscribed and Unsubscribed Events

Those events is disenabled by default, please refer to sys_topics.sys_event_messages to turn it on.

$SYS topic prefix: $SYS/brokers/${node}/clients/

The Payload of the subscribed event message can be parsed into JSON format:

{
    "username":"foo",
    "ts":1625572213878,
    "topic":"/the/best/mqtt/broker/is/emqx",
    "subopts":{
        "sub_props":{},
        "rh":0,
        "rap":0,
        "qos":0,
        "nl":0,
        "is_new":true
    },
    "protocol":"mqtt",
    "clientid":"emqtt-8348fe27a87976ad4db3"
}

The Payload of the unsubscribed event message can be parsed into JSON format:

{
    "username":"foo",
    "ts":1625572213899,
    "topic":"/the/best/mqtt/broker/is/emqx",
    "protocol":"mqtt",
    "clientid":"emqtt-8348fe27a87976ad4db3"
}

Statistics

System topic prefix : $SYS/brokers/${node}/stats/

Client Statistics

Subscription Statistics

Topic Statistics

Routes Statistics

The topics/count and topics/max are numerically equal to routes/count and routes/max.

Throughput (Bytes/Packets/Message) Statistics

System Topic Prefix : $SYS/brokers/${node}/metrics/

Sent and Received Bytes Statistics

Sent and Received MQTT Packets Statistics

MQTT Sent and Received Messages Statistics

Alarms - System Alarms

System Topic Prefix: $SYS/brokers/${node}/alarms/

Sysmon - System Monitoring

System Topic Prefix: $SYS/brokers/${node}/sysmon/