18. Describe the microservice-call-order of deployment as a graph

[trkks]

Author  'juaatark'
Created 2023-03-07T11:53:05.846+02:00
Updated 2023-03-13T18:38:33.682+02:00

This would also require the backend and devices themselves to handle graphs for example as adjacency lists

[trkks]

Author 'juaatark'
Originally created at 2023-03-13T18:27:53.215+02:00

Some stuff in c2318200a2fd045e34310ac97f97802f05f92cec with the linear list of call orders as discussed sometime earlier.

[trkks]

Some thoughts about cycles in the graph:

Example of a cyclic sequence:

• Description: A camera is placed outdoors to detect wildlife from motion sensing. When it gets too dark, a lamp is turned on for getting a better picture and then turned off again. Problem is, the darkness level is calculated programmatically from the image first captured by the camera. This means that camera can be called multiple times but from different sources (first from motion sensor and if the result is too dark, from lamp). If the lamp does not help making the image bright enough, it creates an infinite loop. Also turning on and off the lamp has a similar problem.
• Modules:
  • Motion sensor, 'M'
  • Camera, 'C'
  • Darkness detection, 'D'
  • Lamp, 'L'
  • Object recognition, 'O'
• Sequence:

       - < - - - "lamp on" - - - -
      /                           \
  M -> C -> D - - - "too dark" - - -> L
           \                       / \
            - "enough light" - > -    - "lamp off" -> O

  Possible solutions:

• Have a rule on 'L' to not forward calls needing more light if the same call comes two times "in a row" (current and probably the worst option requiring confusing state management)
• Separate the cyclic calls into three different deployments (deployment creates a "namespace" which prevents described confusion about call source):
  1. pushes images to a shared storage every time the motion sensor goes off
  2. gets notification when images are pushed to the storage, and either turns on the lamp to take a new better picture or turns off the lamp (idempotent)
  3. gets notification when lamp is turned off, fetches latest image from the storage and runs object recognition on it