# MQTT over TCP Bridge

Bridging is a way to connect multiple MQTT broker. Unlike swarms, topic trees and routing tables are not replicated between nodes operating in bridge mode.

Forward the message to the bridge node according to the rules;
Subscribe to the topic from the bridge node, and forward the message in this node/group after collecting the message.

# Configuring

For specific configuration parameters, please refer to configuration the following configuration example is in Hocon format.

Key configuration parameters:

Enable bridge mode: bridges.mqtt.nodes[].enable
Remote broker address: bridges.mqtt.nodes[].connector.server
Forward topic array: bridges.mqtt.nodes[].forwards
Subscribe topic arrary: bridges.mqtt.nodes[].subscription

The bridge configuration part of nanomq.conf:

bridges.mqtt {
	nodes = [ 
		{
			## Bridging Node Name
			name = emqx
			## Enable bridging
			enable = true
			connector {
				## TCP URL format:  mqtt-tcp://host:port
				## TLS URL format:  tls+mqtt-tcp://host:port
				## QUIC URL format: mqtt-quic://host:port
				server = "mqtt-tcp://broker.emqx.io:1883"
				## MQTT protocol version（4 ｜ 5）
				proto_ver = 4
				# username = admin
				# password = public
				clean_start = true
				keepalive = 60s
				ssl {
					enable = false
					keyfile = "/etc/certs/key.pem"
					certfile = "/etc/certs/cert.pem"
					cacertfile = "/etc/certs/cacert.pem"
				}
			}
			forwards = ["forward1/#","forward2/#"]
			subscription = [
				{
					topic = "recv/topic1"
					qos = 1
				},
				{
					topic = "recv/topic2"
					qos = 2
				}
			]
			congestion_control = cubic
			parallel = 2
			max_send_queue_len = 1024
			max_recv_queue_len = 1024
		}
	]
}

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It's available to print more log by setting log.level in the configuration file if needed.

# Running

Start NanoMQ with --conf to specify the configuration file path (if the configuration file is placed in the system path /etc/nanomq.conf, no need to specify on the command line)

$ nanomq start --conf nanomq.conf

# Test bridging

To verify that bridging has succeeded, simply send data to the bridging's upstream and downstream topics, or use mqtt client included in nanomq_cli to verify communication with EMQX 5.0.

# Forwarding messge

1.Subscribe topic from EMQX broker：

Subscribe forward topic forward1/# from EMQX, then will be received the messages from NanoMQ;

Subscribe in the 1st terminal:

$ nanomq_cli sub --url "mqtt-tcp://broker.emqx.io:1883" -t  "forward1/#"
forward1/msg: forward_msg

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Publish message to the topic of local nanomq broker:
Publish message to NanoMQ broker with topic forward1/msg :
Publish in the 2nd terminal:
```
$ nanomq_cli pub -t  "forward1/msg"  -m "forward_msg"
```
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# Subscribing message

Subscribe local topic from NanoMQ broker:
Subscribe topic cmd/topic1 from NanoMQ, then it will be received message from EMQX.
Subscribe in the 3rd terminal:
```
$ nanomq_cli sub -t "recv/topic1"
recv/topic1: cmd_msg
```
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Publish message to remote EMQX broker with topic cmd/topic1:

Publish in the 4th terminal:

$ nanomq_cli pub --url "mqtt-tcp://broker.emqx.io:1883" -t  "recv/topic1" -m "cmd_msg"

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