Moved samara config out of init into connect

[helenosheaa]

This is a fix for if Kafka doesn't connect it wont stop telegraf from starting up

[telegraf-tiger]

🤝 ✅ CLA has been signed. Thank you!

[telegraf-tiger]

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[Hipska]

This only fixes the case for Kafka, but what about the other plugins that have this behaviour? #3723

[helenosheaa]

Thanks @Hipska, the team will revisit that open issue next week and add thoughts/plans to the issue

[ssoroka]

If anyone reading this later is confused, the point of this change is to make it so that Telegraf will not fail to start when this single output has a problem connecting.

To @Hipska 's question, this needs to be addressed on a per-plugin basis. Plugins should use the Init() (capital letter I) function to check config and error on a configuration problem that should prevent Telegraf from starting, and the Connect()/Start() functions for actually connecting to external services; if those return errors they will not prevent Telegraf from starting. Most plugins follow this pattern but a few got it wrong and went unnoticed.

[oplehto]

To @Hipska 's question, this needs to be addressed on a per-plugin basis. Plugins should use the Init() (capital letter I) function to check config and error on a configuration problem that should prevent Telegraf from starting, and the Connect()/Start() functions for actually connecting to external services; if those return errors they will not prevent Telegraf from starting. Most plugins follow this pattern but a few got it wrong and went unnoticed.

100% this ^ Maybe the PR template should even have some checklist item of verifying what are the fatal/non-fatal failure modes and do they conform to the recommended pattern.

[Hipska]

@ssoroka That would be very nice if it is actually true, but this code proves otherwise:

telegraf/agent/agent.go

Lines 253 to 257 in 17e86ab

	err := si.Start(acc)
	if err != nil {
	stopServiceInputs(unit.inputs)
	return nil, fmt.Errorf("starting input %s: %w", input.LogName(), err)
	}

When the Start() returns an error, it will stop all other plugins and then exit..