# InfluxDB Backend

TIP

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

## Wether to add timestamp automatically
backend.influxdb.pool1.set_timestamp = true

backend.influxdb.hook.message.publish.1 = {"topic": "#", "action": {"function": "on_message_publish"}, "pool": "pool1"}
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Parameters in hook rule:

OptionDescription
topicConfigure which topics need to execute hooks
actionConfigure specific action for hook, function is a built-in function provided as Backend for general functions
poolPool 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"}
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# Description of InfluxDB Persistence Hooks

hooktopicactionDescription
message.publish#on_message_publishStore 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>
}
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Template format:

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

PlaceholderDescription
$idMQTT Message UUID, assigned by EMQX
$clientidClient ID used by the Client
$usernameUsername used by the Client
$peerhostIP of Client
$qosQoS of MQTT Message
$topicTopic of MQTT Message
$payloadPayload of MQTT Message, must be valid Json data
$<Number>It must be used with $paylaod to retrieve data from Json Array
$timestampThe 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"
    }
}
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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"
        }
    ]
}
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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"
    }
]
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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"
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# Enable InfluxDB Backend

./bin/emqx_ctl plugins load emqx_backend_influxdb
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