error-handling.md

Error Handling

In general eulabeia sends an info.Failure:

{
  "id": "f704d1e0-768d-4a86-ab6a-dd28e3f45776",
  "created": 443397956,
  "message_type": "failure.modify.target",
  "message_id": "363cde52-e07f-11eb-99c4-6b7f958f017",
  "group_id": "12",
  "error": "Insufficient space",
}

when an error occured while retrieving / already executing a cmd.

Error happening without wrongful usage

This error occurs even when the usage is correct.

For this case most of the modules return the error, so that the cmd can handle the case explicitly.

E.g.: If a director cannot store a target, because there is insufficient space on the device it should:

1. send an info.Failure response so that the client knows that storing failed
2. log the error message
3. exit director with an error code so that it is escalated to the infrastructure (e.g. restart systemd, container)

Response on wrongful usage

This error occurs when a cmd event is containing either:

• wrong values on cmd.Modify
• wrong ID on cmd.Start, cmd.Get, cmd.Stop, ...

In this case eulabeia will not return an error to the module user but rather

1. send an info.Failure response to that the client can resend a correct cmd

eulabeia does not handle unknown messages as errors, but is returning a info.Failure when the topic is correct and the message contains correct eulabeia meta-data. Otherwise a unknown message will be ignored.

This allows to run different version of eulabeia in parallel without having to concern about new cmds and it allows deployment methods like blue/green on a large network of sensors, without having to deal with restart spam but still having the chance to monitor weird behaviour, e.g. when a sensor wasn't updated but should be.