InfluxDB Backend

InfluxDB Backend

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After EMQX version 3.1, a powerful rule engine is introduced to replace plug-ins. It is recommended that you use it. See Save data to InfluxDB to setup Save data to InfluxDB in rule engine.

Configure InfluxDB Server

Config file: etc/plugins/emqx_backend_influxdb.conf:

## InfluxDB UDP Server
backend.influxdb.pool1.server = 127.0.0.1:8089
## InfluxDB Pool Size
backend.influxdb.pool1.pool_size = 5
## Whether to add timestamp automatically
backend.influxdb.pool1.set_timestamp = true
backend.influxdb.hook.message.publish.1 = {"topic": "#", "action": {"function": "on_message_publish"}, "pool": "pool1"}

Parameters in hook rule:

Option	Description
topic	Configure which topics need to execute hooks
action	Configure specific action for hook, `function` is a built-in function provided as Backend for general functions
pool	Pool Name, used to connect multiple InfluxDB servers

Example:

## Store PUBLISH message whose topic is "sensor/#"
backend.influxdb.hook.message.publish.1 = {"topic": "sensor/#", "action": {"function": "on_message_publish"}, "pool": "pool1"}
## Store PUBLISH message whose topic is "stat/#"
backend.influxdb.hook.message.publish.2 = {"topic": "stat/#", "action": {"function": "on_message_publish"}, "pool": "pool1"}

Description of InfluxDB Persistence Hooks

hook	topic	action	Description
message.publish	#	on_message_publish	Store published messages

Since MQTT Message cannot be written directly to InfluxDB, InfluxDB Backend provides an emqx_backend_influxdb.tmpl template file to convert MQTT Message to DataPoint that can be written to InfluxDB.

Template file use Json format:

key - MQTT Topic, Json String, support wildcard characters
value - Template, Json Object, used to convert MQTT Message into measurement,tag_key=tag_value,... field_key=field_value,... timestamp and write to InfluxDB。

You can define different templates for different topics or multiple templates for the same topic, likes:

{
    <Topic 1>: <Template 1>,
    <Topic 2>: <Template 2>
}

Template format:

{
    "measurement": <Measurement>,
    "tags": {
        <Tag Key>: <Tag Value>
    },
    "fields": {
        <Field Key>: <Field Value>
    },
    "timestamp": <Timestamp>
}

measurement and fields are required options, tags and timestamp are optional.

All values (such as <Measurement>) can be configured directly in the template as a fixed value that data types supported depending on the table you define. More realistically, of course, you can access the data in the MQTT message through the placeholder we provide.

Currently, we support placeholders as follows:

Placeholder	Description
$id	MQTT Message UUID, assigned by EMQX
$clientid	Client ID used by the Client
$username	Username used by the Client
$peerhost	IP of Client
$qos	QoS of MQTT Message
$topic	Topic of MQTT Message
$payload	Payload of MQTT Message, must be valid Json data
$<Number>	It must be used with $paylaod to retrieve data from Json Array
$timestamp	The timestamp EMQX sets when preparing to forward messages, precision: Nanoseconds

$payload and $<Number>:

You can directly use $content to obtain the complete message payload, you can use ["$payload", <Key>, ...] to get the data inside the message payload.

For example payload is {"data": {"temperature": 23.9}}, you can via ["$payload", "data", "temperature"] to get 23.9.

In the case of array data type in Json, we introduced $0 and $<pos_integer>, $0 means to get all elements in the array, and $<pos_integer> means to get the <pos_integer>th element in the array.

A simple example, ["$payload", "$0", "temp"] will get [20, 21] from [{"temp": 20}, {"temp": 21}], and ["$payload", "$1", "temp"] will only get 20.

It is worth noting that when you use $0, we expect the number of data you get is same. Because we need to convert these arrays into multiple records and write it into InfluxDB, and when you have three pieces of data in one field and two in another, we won’t know how to combine the data for you.

Example

data/templates directory provides a sample template (emqx_backend_influxdb_example.tmpl, please remove the “_example” suffix from the filename when using it formally) for the user’s reference:

{
    "sample": {
        "measurement": "$topic",
        "tags": {
            "host": ["$payload", "data", "$0", "host"],
            "region": ["$payload", "data", "$0", "region"],
            "qos": "$qos",
            "clientid": "$clientid"
        },
        "fields": {
            "temperature": ["$payload", "data", "$0", "temp"]
        },
        "timestamp": "$timestamp"
    }
}

When an MQTT Message whose Topic is “sample” has the following Payload:

{
    "data": [
        {
            "temp": 1,
            "host": "serverA",
            "region": "hangzhou"
        },
        {
            "temp": 2,
            "host": "serverB",
            "region": "ningbo"
        }
    ]
}

Backend converts MQTT messages to:

[
    {
        "measurement": "sample",
        "tags": {
            "clientid": "mqttjs_ebcc36079a",
            "host": "serverA",
            "qos": "0",
            "region": "hangzhou",
        },
        "fields": {
            "temperature": "1"
        },
        "timestamp": "1560743513626681000"
    },
    {
        "measurement": "sample",
        "tags": {
            "clientid": "mqttjs_ebcc36079a",
            "host": "serverB",
            "qos": "0",
            "region": "ningbo",
        },
        "fields": {
            "temperature": "2"
        },
        "timestamp": "1560743513626681000"
    }
]

The data was finally encoded and written to InfluxDB as follows:

"sample,clientid=mqttjs_6990f0e886,host=serverA,qos=0,region=hangzhou temperature=\"1\" 1560745505429670000\nsample,clientid=mqttjs_6990f0e886,host=serverB,qos=0,region=ningbo temperature=\"2\" 1560745505429670000\n"

Enable InfluxDB Backend

./bin/emqx_ctl plugins load emqx_backend_influxdb