Auto Subscribe

With Auto Subscription enabled, after a client is successfully connected to EMQX, it may not need to send SUBSCRIBE requests to EMQX, because EMQX will complete the pre-defined subscriptions for the client.

Prior to version 5, this feature is also known as "proxy subscription".

# Configuration

# Configuration Definition

Field	Definition	Range	Default
auto_subscribe	Auto subscribe configurations	topics	topics
topics	Subscription Options	Subscription configurations list. See `Subscription Option`	[]

# Subscription Option

Field	Definition	Range	Default
topic	Required. Topic	String, placeholders supported	No default value
qos	Not Required. Subscription QoS	0 or 1 or 2. Refer to the MQTT QoS definition	0
rh	Not Required. MQTT version 5.0. Whether to send retain message when a subscription is created.	0: Not send the retain message 1: Send the retain message	0
rap	Not Required. MQTT version 5.0. When forwarding messages, Whether to send with retain flag	0: Set retain 0 1: Keep retain flag	0
nl	Not Required. MQTT version 5.0. Whether the message can be forwarded to the client when published by itself	0: Forwarded to self 1: Not forwarded to self	0

# Subscription Placeholders

Placeholder	Definition
${clientid}	Client ID
${username}	Client Username
${ip}	Client TCP connection local IP address
${port}	Client TCP connection local Port

# Quick Start

Add the following configuration items to the configuration file

auto_subscribe {
    topics = [
        {
            topic = "c/${clientid}"
        },
        {
            topic = "client/${clientid}/username/${username}/host/${host}/port/${port}"
            qos   = 1
            rh    = 0
            rap   = 0
            nl    = 0
        }
    ]
}

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+---------------------------+             +----------------+
| clientid: demo_client1    |             |  EMQX Broker   |
| username: admin           |             |                |
| local host: 192.168.1.234 |&lt;----------->|                |
| local port: 55678         |             |                |
+---------------------------+             +----------------+

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When the client uses versions lower than 5, the following subscriptions are available after connection.

topic: c/demo_client1
qos: 0

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topic: client/demo_client1/username/admin/host/192.168.1.234/port/55678
qos: 1

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When the client uses version 5, the following subscriptions are available after connection.

topic: c/demo_client1
qos: 0
rh: 0
rap: 0
nl: 0

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topic: client/demo_client1/username/admin/host/192.168.1.234/port/55678
qos: 1
rh: 0
rap: 0
nl: 0