# MQTT source 

eKuiper provides built-in support for MQTT source stream, which can subscribe the message from MQTT broker and feed into the eKuiper processing pipeline.  The configuration file of MQTT source is at ``$ekuiper/etc/mqtt_source.yaml``. Below is the file format.

```yaml
#Global MQTT configurations
default:
  qos: 1
  servers: [tcp://127.0.0.1:1883]
  #username: user1
  #password: password
  #certificationPath: /var/kuiper/xyz-certificate.pem
  #privateKeyPath: /var/kuiper/xyz-private.pem.key
  #rootCaPath: /var/kuiper/xyz-rootca.pem
  #insecureSkipVerify: true
  #connectionSelector: mqtt.mqtt_conf1


#Override the global configurations
demo_conf: #Conf_key
  qos: 0
  servers: [tcp://10.211.55.6:1883, tcp://127.0.0.1]

```

## Global MQTT configurations

Use can specify the global MQTT settings here. The configuration items specified in ``default`` section will be taken as default settings for all MQTT connections. 

### qos

The default subscription QoS level.

### servers

The server list for MQTT message broker. Currently, only ``ONE`` server can be specified.

### username

The username for MQTT connection. 

### password

The password for MQTT connection.

### protocolVersion

MQTT protocol version. 3.1 (also refer as MQTT 3) or 3.1.1 (also refer as MQTT 4). If not specified, the default value is 3.1.

### clientid

The client id for MQTT connection. If not specified, an uuid will be used.


### certificationPath

The location of certification path. It can be an absolute path, or a relative path. If it is an relative path, then the base path is where you excuting the ``kuiperd`` command. For example, if you run ``bin/kuiperd`` from ``/var/kuiper``, then the base path is ``/var/kuiper``; If you run ``./kuiperd`` from ``/var/kuiper/bin``, then the base path is ``/var/kuiper/bin``.  Such as  ``d3807d9fa5-certificate.pem``.

### privateKeyPath

The location of private key path. It can be an absolute path, or a relative path.  For more detailed information, please refer to ``certificationPath``. Such as ``d3807d9fa5-private.pem.key``.

### rootCaPath

The location of root ca path. It can be an absolute path, or a relative path.

### insecureSkipVerify

Control if to skip the certification verification. If it is set to true, then skip certification verification; Otherwise, verify the certification

### connectionSelector

specify the stream to reuse the connection to mqtt broker. The connection profile located in ``connections/connection.yaml``.
```yaml
mqtt:
  localConnection: #connection key
    servers: [tcp://127.0.0.1:1883]
    username: ekuiper
    password: password
    #certificationPath: /var/kuiper/xyz-certificate.pem
    #privateKeyPath: /var/kuiper/xyz-private.pem.ke
    #insecureSkipVerify: false
    #protocolVersion: 3
    clientid: ekuiper
  cloudConnection: #connection key
    servers: ["tcp://broker.emqx.io:1883"]
    username: user1
    password: password
    #certificationPath: /var/kuiper/xyz-certificate.pem
    #privateKeyPath: /var/kuiper/xyz-private.pem.ke
    #insecureSkipVerify: false
    #protocolVersion: 3

```
There are two configuration groups for mqtt in the example, user need use ``mqtt.localConnection`` or ``mqtt.cloudConnection`` as the selector.
For example
```yaml
#Global MQTT configurations
default:
  qos: 1
  servers: [tcp://127.0.0.1:1883]
  #username: user1
  #password: password
  #certificationPath: /var/kuiper/xyz-certificate.pem
  #privateKeyPath: /var/kuiper/xyz-private.pem.key
  connectionSelector: mqtt.localConnection
```
*Note*: once specify the connectionSelector in specific configuration group , all connection related parameters will be ignored , in this case ``servers: [tcp://127.0.0.1:1883]``

### bufferLength

specify the maximum number of messages to be buffered in the memory. This is used to avoid the extra large memory usage that would cause out of memory error. Notice that the memory usage will be varied to the actual buffer. Increase the length here won't increase the initial memory allocation so it is safe to set a large buffer length. The default value is 102400, that is if each payload size is about 100 bytes, the maximum buffer size will be about 102400 * 100B ~= 10MB.

### kubeedgeVersion

kubeedge version number. Different version numbers correspond to different file contents.

### kubeedgeModelFile

The name of the kubeedge template file. The file is located in the specified etc/sources folder. The sample format is as follows:

```json
{
	"deviceModels": [{
		"name": "device1",
		"properties": [{
			"name": "temperature",
			"dataType": "int"
		}, {
			"name": "temperature-enable",
			"dataType": "string"
		}]
	}]
}
```

#### deviceModels.name

The device name. It matches the field in the subscription topic that is located between the third and fourth "/". For example: $ke/events/device/device1/data/update.

#### properties.name

Field name.

#### properties.dataType

Expected field type.

## Override the default settings

If you have a specific connection that need to overwrite the default settings, you can create a customized section. In the previous sample, we create a specific setting named with ``demo``.  Then you can specify the configuration with option ``CONF_KEY`` when creating the stream definition (see [stream specs](../../sqls/streams.md) for more info).

**Sample**

```
demo (
		...
	) WITH (DATASOURCE="test/", FORMAT="JSON", KEY="USERID", CONF_KEY="demo");
```

The configuration keys used for these specific settings are the same as in ``default`` settings, any values specified in specific settings will overwrite the values in ``default`` section.