Beats silently fails to start any input if there is an error when parsing the units sent by Elastic-Agent

[belimawr]

When running under Elastic-Agent, if at least one unit has got an invalid configuration the Beat will silently fail without starting any input or producing any error log. During policy changes, it will log the received units, however they will never be started.

generateBeatConfig returns an error that reloadInputs correctly wraps, however it is not correctly handled by reload

When reload receives an error from reloadInputs, it will check if it is a list of errors, if it is, it correctly handles them, if it is not, then no error is handled and the code proceeds as if reloadInputs had succeeded.

beats/x-pack/libbeat/management/managerV2.go

Lines 683 to 703 in acce29c

	if err := cm.reloadInputs(inputUnits); err != nil { // HERE
	// cm.reloadInputs will use fmt.Errorf and join an error slice
	// using errors.Join, so we need to unwrap the fmt wrapped error,
	// then we can iterate over the errors list.
	err = errors.Unwrap(err)
	type unwrapList interface {
	Unwrap() []error
	}
	//nolint:errorlint // That's a custom logic based on how reloadInputs builds the error
	errList, isErrList := err.(unwrapList)
	if isErrList {
	for _, err := range errList.Unwrap() {
	unitErr := cfgfile.UnitError{}
	if errors.As(err, &unitErr) {
	unitErrors[unitErr.UnitID] = append(unitErrors[unitErr.UnitID], unitErr.Err)
	delete(healthyInputs, unitErr.UnitID)
	}
	}
	}
	}

This can be easily reproduced by adding the following (invalid) input configuration to an Elastic-Agent policy:

  - id: logfile-sample-2a176a73-63a4-448a-b208-bea77259a9ba
    name: threat_map-1
    revision: 1
    type: logfile
    use_output: default
    meta:
      package:
        name: threat_map
        version: 0.2.0
    data_stream:
      namespace: default
    package_policy_id: 2a176a73-63a4-448a-b208-bea77259a9ba

The Threat Map integration is currently generating this input, there is an open issue about it: elastic/integrations#13017

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)