Handle empty event response

[sarita-maersk]

Currently when there are no events scheduled for a node, the endpoint
curl -H Metadata:true http://169.254.169.254/metadata/scheduledevents?api-version=2020-07-01

• either returns a valid object with empty events array as shown in Scenario-1
• or returns empty response as shown in Scenario-2

Scenario-1

Scenarioa-2

In our Azure nodes, the termination handler has been exclusively logging json unmarshal errors as the node's scheduled events response is empty.

{
  "error": "error in json.Unmarshal: unexpected end of JSON input",
  "level": "error",
  "msg": "",
  "time": "2024-01-30T15:27:06Z"
}

Receiving empty response from the scheduled events endpoint is a valid scenario, we should not treat this as an error. In this PR we are logging the required message at info level and returns no error if the response body is empty.

[maksim-paskal]

@sarita-maersk thanks for your contribution, I never see that behavior in our clusters, in documentation that also never been mention. But if you see that errors in real life - agree, seems that we needed that changed.

How frequently you see that error in your clusters? What about raise log level to WARN?

There are some linter issue, please fix that.

[sarita-maersk]

Thank you @maksim-paskal for the quick review. Please find my response inline.

How frequently you see that error in your clusters?

We run ~350 spot nodes in our telemetry cluster and the frequency of this error ranges from 1000 to 10,000 in a span of 24hrs.

---

What about raise log level to WARN?

Since Azure document doesn't mention anything about empty response, I am in favour of making this log level to WARN.

There are some linter issue, please fix that.

Fixed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2a91db7) 98.53% compared to head (ac09ac8) 98.53%.

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Additional details and impacted files

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##             main      #70   +/-   ##
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  Coverage   98.53%   98.53%           
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  Files           6        6           
  Lines         205      205           
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  Hits          202      202           
  Misses          2        2           
  Partials        1        1           

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[maksim-paskal]

@sarita-maersk, your changes were released. I also added debug logs for requests in the new release. This can help us debug other responses that aren't well-documented in the future.

Thank for your contribution!