Rules

Rules are defined by JSON, below is an example.

{
  "id": "rule1",
  "sql": "SELECT demo.temperature, demo1.temp FROM demo left join demo1 on demo.timestamp = demo1.timestamp where demo.temperature > demo1.temp GROUP BY demo.temperature, HOPPINGWINDOW(ss, 20, 10)",
  "actions": [
    {
      "log": {}
    },
    {
      "mqtt": {
        "server": "tcp://47.52.67.87:1883",
        "topic": "demoSink"
      }
    }
  ]
}

The following 3 parameters are required for creating a rule.

Parameters

id

The identification of the rule. The rule name cannot be duplicated in the same eKuiper instance.

sql

The sql query to run for the rule.

Options

The current options includes:

For detail about qos and checkpointInterval, please check state and fault tolerance.

The rule options can be defined globally in etc/kuiper.yaml under the rules section. The options defined in the rule json will override the global setting.

Sources

• eKuiper provides embeded following 3 sources,
  • MQTT source, see MQTT source stream for more detailed info.
  • EdgeX source by default is shipped in docker images, but NOT included in single download binary files, you use make pkg_with_edgex command to build a binary package that supports EdgeX source. Please see EdgeX source stream for more detailed info.
  • HTTP pull source, regularly pull the contents at user’s specified interval time, see here for more detailed info.
• See SQL for more info of eKuiper SQL.
• Sources can be customized, see extension for more detailed info.

Sinks/Actions

Currently, below kinds of sinks/actions are supported:

• log: Send the result to log file.
• mqtt: Send the result to an MQTT broker.
• edgex: Send the result to EdgeX message bus.
• rest: Send the result to a Rest HTTP server.
• nop: Send the result to a nop operation.

Each action can define its own properties. There are several common properties:

Data Template

User can refer to Use Golang template to customize analaysis result in eKuiper for more detailed scenarios. If sendSingle is true, the data template will execute against a record; Otherwise, it will execute against the whole array of records. Typical data templates are:

For example, we have the sink input as

[]map[string]interface{}{{
    "ab" : "hello1",
},{
    "ab" : "hello2",
}}

In sendSingle=true mode:

• Print out the whole record

"dataTemplate": "{\"content\":{{json .}}}",

• Print out the ab field

"dataTemplate": "{\"content\":{{.ab}}}",

if the ab field is a string, add the quotes

"dataTemplate": "{\"content\":\"{{.ab}}\"}",

In sendSingle=false mode:

• Print out the whole record array

"dataTemplate": "{\"content\":{{json .}}}",

• Print out the first record

"dataTemplate": "{\"content\":{{json (index . 0)}}}",

• Print out the field ab of the first record

"dataTemplate": "{\"content\":{{index . 0 \"ab\"}}}",

• Print out field ab of each record in the array to html format

"dataTemplate": "<div>results</div><ul>{{range .}}<li>{{.ab}}</li>{{end}}</ul>",

Actions could be customized to support different kinds of outputs, see extension for more detailed info.

Functions supported in template

With the help of template functions, users can do a lot of transformation including formation, simple mathematics, encoding etc. The supported functions in eKuiper template includes:

1. Go built-in template functions.
2. An abundant extended function set from sprig library.
3. eKuiper extended functions.

eKuiper extends several functions that can be used in data template.

• (deprecated)json para1: The json function is used for convert the map content to a JSON string. UsetoJson from sprig instead.
• (deprecated)base64 para1: The base64 function is used for encoding parameter value to a base64 string. Convert the pramater to string type and use b64enc from sprig instead.

Dynamic properties

In the sink, it is common to fetch a property value from the result data to achieve dynamic output. For example, to write data into a dynamic topic of mqtt. The dynamic properties will be parsed as a data template. In below example, the sink topic is gotten from the selected topic using data template.

{
  "id": "rule1",
  "sql": "SELECT topic FROM demo",
  "actions": [{
    "mqtt": {
      "sendSingle": true,
      "topic": "prefix/{{.topic}}"
    }
  }]
}

In the above example, sendSingle property is used, so the sink data is a map by default. If not using sendSingle, you can get the topic by index with data template {{index . 0 “topic”}}.