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https://github.com/emqx/emqx-bridge-mqtt

Bridge of MQTT (deprecated since EMQX v5)
https://github.com/emqx/emqx-bridge-mqtt

bridge-emq emqx mqtt-bridge mqtt-broker

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Bridge of MQTT (deprecated since EMQX v5)

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# EMQ Bridge MQTT



NOTE: Since EMQX v5, this repo has been moved to the monorepo: https://github.com/emqx/emqx/tree/master/apps/emqx_bridge_mqtt



The concept of **Bridge** means that EMQ X supports forwarding messages

of one of its own topics to another MQTT Broker in some way.



**Bridge** differs from **Cluster** in that the bridge does not

replicate the topic trie and routing tables and only forwards MQTT

messages based on bridging rules.



At present, the bridging methods supported by EMQ X are as follows:



-   RPC bridge: RPC Bridge only supports message forwarding and does not

    support subscribing to the topic of remote nodes to synchronize

    data;

-   MQTT Bridge: MQTT Bridge supports both forwarding and data

    synchronization through subscription topic.



These concepts are shown below:



![bridge](docs/images/bridge.png)



In addition, the EMQ X message broker supports multi-node bridge mode interconnection



```

              ---------                     ---------                     ---------

Publisher --> | Node1 | --Bridge Forward--> | Node2 | --Bridge Forward--> | Node3 | --> Subscriber

              ---------                     ---------                     ---------

```



In EMQ X, bridge is configured by modifying `etc/emqx.conf`. EMQ X distinguishes between different bridges based on different names. E.g



```

## Bridge address: node name for local bridge, host:port for remote.

bridge.mqtt.aws.address = 127.0.0.1:1883

```



This configuration declares a bridge named `aws` and specifies that it is bridged to the MQTT broker of 127.0.0.1:1883 by MQTT mode.



In case of creating multiple bridges, it is convenient to replicate all configuration items of the first bridge, and modify the bridge name and other configuration items if necessary (such as bridge.$name.address, where $name refers to the name of bridge)



The next two sections describe how to create a bridge in RPC and MQTT mode respectively and create a forwarding rule that forwards the messages from sensors. Assuming that two EMQ X nodes are running on two hosts:



| Name | Node              | MQTT Port |

|------|-------------------|-----------|

| emqx1| [email protected].| 1883      |

| emqx2| [email protected] | 1883      |



## EMQ X RPC Bridge Configuration



The following is the basic configuration of RPC bridging. A simplest RPC bridging only requires the following three items



```

## Bridge Address: Use node name (nodename@host) for rpc bridging, and host:port for mqtt connection

bridge.mqtt.emqx2.address = [email protected]



## Forwarding topics of the message

bridge.mqtt.emqx2.forwards = sensor1/#,sensor2/#



## bridged mountpoint

bridge.mqtt.emqx2.mountpoint = bridge/emqx2/${node}/

```



If the messages received by the local node emqx1 matches the topic `sersor1/#` or `sensor2/#`, these messages will be forwarded to the `sensor1/#` or `sensor2/#` topic of the remote node emqx2.



`forwards` is used to specify topics. Messages of the in `forwards` specified topics on local node are forwarded to the remote node.



`mountpoint` is used to add a topic prefix when forwarding a message. To use `mountpoint`, the `forwards` directive must be set. In the above example, a message with the topic `sensor1/hello` received by the local node will be forwarded to the remote node with the topic `bridge/emqx2/[email protected]/sensor1/hello`.



Limitations of RPC bridging:



1. The RPC bridge of emqx can only forward local messages to the remote node, and cannot synchronize the messages of the remote node to the local node;



2. RPC bridge can only bridge two EMQ X broker together and cannot bridge EMQ X broker to other MQTT brokers.



## EMQ X MQTT Bridge Configuration



EMQ X 3.0 officially introduced MQTT bridge, so that EMQ X can bridge any MQTT broker. Because of the characteristics of the MQTT protocol, EMQ X can subscribe to the remote mqtt broker's topic through MQTT bridge, and then synchronize the remote MQTT broker's message to the local.



EMQ X MQTT bridging principle: Create an MQTT client on the EMQ X broker, and connect this MQTT client to the remote MQTT broker. Therefore, in the MQTT bridge configuration, following fields may be set for the EMQ X to connect to the remote broker as an mqtt client



```

## Bridge Address: Use node name for rpc bridging, use host:port for mqtt connection

bridge.mqtt.emqx2.address = 192.168.1.2:1883



## Bridged Protocol Version

## Enumeration value: mqttv3 | mqttv4 | mqttv5

bridge.mqtt.emqx2.proto_ver = mqttv4



## mqtt client's clientid

bridge.mqtt.emqx2.clientid = bridge_emq



## mqtt client's clean_start field

## Note: Some MQTT Brokers need to set the clean_start value as `true`

bridge.mqtt.emqx2.clean_start = true



##  mqtt client's username field

bridge.mqtt.emqx2.username = user



## mqtt client's password field

bridge.mqtt.emqx2.password = passwd



## Whether the mqtt client uses ssl to connect to a remote serve or not

bridge.mqtt.emqx2.ssl = off



## CA Certificate of Client SSL Connection (PEM format)

bridge.mqtt.emqx2.cacertfile = etc/certs/cacert.pem



## SSL certificate of Client SSL connection 

bridge.mqtt.emqx2.certfile = etc/certs/client-cert.pem



## Key file of Client SSL connection 

bridge.mqtt.emqx2.keyfile = etc/certs/client-key.pem



## SSL encryption

bridge.mqtt.emqx2.ciphers = ECDHE-ECDSA-AES256-GCM-SHA384,ECDHE-RSA-AES256-GCM-SHA384



## TTLS PSK password

## Note 'listener.ssl.external.ciphers' and 'listener.ssl.external.psk_ciphers' cannot be configured at the same time

##

## See 'https://tools.ietf.org/html/rfc4279#section-2'.

## bridge.mqtt.emqx2.psk_ciphers = PSK-AES128-CBC-SHA,PSK-AES256-CBC-SHA,PSK-3DES-EDE-CBC-SHA,PSK-RC4-SHA



## Client's heartbeat interval

bridge.mqtt.emqx2.keepalive = 60s



## Supported TLS version

bridge.mqtt.emqx2.tls_versions = tlsv1.2,tlsv1.1,tlsv1



## Forwarding topics of the message

bridge.mqtt.emqx2.forwards = sensor1/#,sensor2/#



## Bridged mountpoint

bridge.mqtt.emqx2.mountpoint = bridge/emqx2/${node}/



## Subscription topic for bridging

bridge.mqtt.emqx2.subscription.1.topic = cmd/topic1



## Subscription qos for bridging

bridge.mqtt.emqx2.subscription.1.qos = 1



## Subscription topic for bridging

bridge.mqtt.emqx2.subscription.2.topic = cmd/topic2



## Subscription qos for bridging

bridge.mqtt.emqx2.subscription.2.qos = 1



## Bridging reconnection interval

## Default: 30s

bridge.mqtt.emqx2.reconnect_interval = 30s



## QoS1 message retransmission interval

bridge.mqtt.emqx2.retry_interval = 20s



## Inflight Size.

bridge.mqtt.emqx2.max_inflight_batches = 32

```



## Bridge Cache Configuration



The bridge of EMQ X has a message caching mechanism. The caching mechanism is applicable to both RPC bridging and MQTT bridging. When the bridge is disconnected (such as when the network connection is unstable), the messages with a topic specified in `forwards` can be cached to the local message queue. Until the bridge is restored, these messages are re-forwarded to the remote node. The configuration of the cache queue is as follows



```

## emqx_bridge internal number of messages used for batch

bridge.mqtt.emqx2.queue.batch_count_limit = 32



##  emqx_bridge internal number of message bytes used for batch

bridge.mqtt.emqx2.queue.batch_bytes_limit = 1000MB



## The path for placing replayq queue. If it is not specified, then replayq will run in `mem-only` mode and messages will not be cached on disk.

bridge.mqtt.emqx2.queue.replayq_dir = data/emqx_emqx2_bridge/

    

## Replayq data segment size

bridge.mqtt.emqx2.queue.replayq_seg_bytes = 10MB

```



`bridge.mqtt.emqx2.queue.replayq_dir` is a configuration parameter for specifying the path of the bridge storage queue.



`bridge.mqtt.emqx2.queue.replayq_seg_bytes` is used to specify the size of the largest single file of the message queue that is cached on disk. If the message queue size exceeds the specified value, a new file is created to store the message queue.



## CLI for EMQ X Bridge MQTT



CLI for EMQ X Bridge MQTT:



``` bash

$ cd emqx1/ && ./bin/emqx_ctl bridges

bridges list                                  # List bridges

bridges start                           # Start a bridge

bridges stop                            # Stop a bridge

bridges forwards                        # Show a bridge forward topic

bridges add-forward              # Add bridge forward topic

bridges del-forward              # Delete bridge forward topic

bridges subscriptions                   # Show a bridge subscriptions topic

bridges add-subscription    # Add bridge subscriptions topic

```



List all bridge states



``` bash

$ ./bin/emqx_ctl bridges list

name: emqx     status: Stopped    $ ./bin/emqx_ctl bridges list

name: emqx     status: Stopped

```



Start the specified bridge



``` bash

$ ./bin/emqx_ctl bridges start emqx

Start bridge successfully.

```



Stop the specified bridge



``` bash

$ ./bin/emqx_ctl bridges stop emqx

Stop bridge successfully.

```

List the forwarding topics for the specified bridge



``` bash

$ ./bin/emqx_ctl bridges forwards emqx

topic:   topic1/#

topic:   topic2/#

```



Add a forwarding topic for the specified bridge



``` bash

$ ./bin/emqx_ctl bridges add-forwards emqx topic3/#

Add-forward topic successfully.

```



Delete the forwarding topic for the specified bridge



``` bash

$ ./bin/emqx_ctl bridges del-forwards emqx topic3/#

Del-forward topic successfully.

```



List subscriptions for the specified bridge



``` bash

$ ./bin/emqx_ctl bridges subscriptions emqx

topic: cmd/topic1, qos: 1

topic: cmd/topic2, qos: 1

```



Add a subscription topic for the specified bridge



``` bash

$ ./bin/emqx_ctl bridges add-subscription emqx cmd/topic3 1

Add-subscription topic successfully.

```



Delete the subscription topic for the specified bridge



``` bash

$ ./bin/emqx_ctl bridges del-subscription emqx cmd/topic3

Del-subscription topic successfully.

```



Note: In case of creating multiple bridges, it is convenient to replicate all configuration items of the first bridge, and modify the bridge name and other configuration items if necessary.