metricq-combinator

This tool is a MetricQ transformer that produces new, user-defined metrics (called combined metrics) as arithmetic combinations of existing metrics (called input metrics).

Building

Build using cmake:

$ mkdir build && cd build
$ cmake ..
$ make

Usage

Basic setup (MetricQ management server, token etc) is configured via command line; for more information, issue:

$ metricq-combinator --help

The actual information on how to combine new metrics is provided as a JSON object by the management server, mapping the names of metrics-to-be-combined to their configuration:

{
   "metrics": {
      <name of combined metric>: {
         "expression": <expression>,
         "metadata": { ... }
      },
      ...
   }
}

For each combined metric, the key "expression" is mandatory and describes this metric as a tree of operations and input metrics/constants:

<expression> ::= "<input metric>"
<expression> ::= <constant value (float/integer)>
<expression> ::= {
                     "operation": ("+" | "-" | "*" | "/"),
                     "left": <expression>,
                     "right": <expression>
                 }
<expression> ::= {
                     "operation": ("min" | "max" | "sum"),
                     "inputs": [<expression>, ...]
                 }
<expression> ::= {
                     "operation": "throttle",
                     "cooldown_period": "<duration>",
                     "input": <expression>
                 }

where <duration> is of the form <value><unit>, e.g. 2s or 500 milliseconds.

The key "metadata" is optional and maps to a JSON object containing arbitrary metadata for this combined metric. These are sent to the manager when declaring the new metric. Commonly used metadata-keys are:

"unit"

A string containing the SI unit symbol in which this metric reports values.

"description"

A string containing the human-readable description of what this metric reports.

"display_expression"

A string containing a human-readable version of this metrics "expression"-key, i.e. a short description on how this metric is derived from its inputs, in infix-notation.

"rate"

A number describing the rate (in Hz) at which this metric is expected to produce values. For example, a metric with "rate": 0.2 should report a new value every ~5 seconds, i.e. at a rate of 1/5 Hz.

Examples

• Report the total power consumption of two systems foo and bar as a new metric foobar.power:

  "foobar.power": {
     "expression": {
        "left":      "foo.power",
        "operation": "+"
        "right":     "bar.power",
     },
     "metadata": {
        "unit": "W",
        "description": "Total power consumption of foo and bar",
        "display_expression": "foo.power + bar.power",
     }
  }
  

• Provide a temperature reading in a different unit:

  "RoomA15.temperature.imperial": {
    "expression": {
      "left": {
         "left": "RoomA15.temperature",
         "right": 1.8,
         "operation": "*"
      },
      "right": 32,
      "operation": "+"
    },
    "metadata": {
      "unit": "°F",
      "description": "Room A15 temperature reading, in degrees Fahrenheit"
      "display_expression": "(RoomA15.temperature * 9/5) + 32"
    }
  }
  

License

Combine new MetricQ metrics in a flexible way
Copyright (C) 2019  Technische Universität Dresden

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.