Allow addressing by ID instead of "analog input" etc

[RichiH]

@mxinden

A default config should probably come with comments to allow people familiar with Modbus to know where to put things in the config and keep a mental map. That being said, addressing by "coil" and other such names seems cumbersome and error-prone. Addressing by ID directly seems better.

Sub-addressing could be done by id:bit, ranges could be done explicitly by id-idN or implicitly by id, float32, little endian.

Gut feeling is that we will develop stronger opinions when using it for some time.

[RichiH]

@mxinden This is not yet done, correct?

[RichiH]

Seems it's not, yet.

CC @bastischubert

[RichiH]

Disregarding that joule as an absolute would be better as we can calculate Wh as a rate() from there, I think this would be the better model. Current style:

  - name: 'dcim_power_consumption-xxx'
    protocol: 'tcp/ip'
    id: 2
    analogOut:
      - name: power_consumed_watt_hours
        help: 'Power Consumtion in WattHours'
        address: 1226
        metricType: counter
        labels:
          datacenter: 'Halma'
          room: 'xx'
          rack: 'xx'
          fuse: 'xx'
          customer: 'xx'
          billable: 'xx'
        dataType: float32

Proposed new style:

pre-amble block for the whole target, or exporter instance
  - protocol: 'tcp/ip'
    id: 2 << what is this? Is it unique? Or can it go into pre-amble?

    address: 1226 << this could either be keyed by address, or name. But given that the address is static, it should most likely be keyed by address
        name: 'power_consumed_watt_hours'
        help: 'Power Consumtion in WattHours'
        metricType: counter
        dataType: float32
        labels:
          datacenter: 'xx'
          room: 'xx'
          rack: 'xx'
          fuse: 'xx'
          customer: 'xx'
          billable: 'xx'

[mxinden]

`id: 2 << what is this? Is it unique? Or can it go into pre-amble?`

The id field or SlaveID is used whenever one talks to a gateway (e.g. TCP/IP gateway) instead of straight to a modbus device. The id is used to multiplex the request to the right device behind the gateway. See http://docs.tibbo.com/tmgm/slave-id-based-routing.htm for more details.

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In regards to the proposed changed format:

• Prometheus needs a way to address the specific module via a module http parameter in the configuration file. Thus dropping the name property of a module definition makes this addressing impossible. Is there a particular reason why you want to drop it?

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In regards to changing addressing via ID instead of analog in/out or digital in/out there is a third option: Reading more and more modbus documentations it seems like another specification is function codes see the Wikipedia article.

As of today the specification via analog in/out or digital in/out seems to work for our generated configuration. For now, given that this is not blocking any functionality, I would suggest postponing this change until we have more feedback by other users in regards to their preference.