Error when --es.use-ilm is set without --es.use-aliases

[albertteoh]

Requirement - what kind of business use case are you trying to solve?

--es.use-ilm must always be used in conjunction with --es.use-aliases to ensure ES writers and readers refer to the single index mapping. Otherwise, ILM will not work as it does not have a rollover alias to work on.

As such, we should provide a useful error to users who mistakenly set --es.use-ilm without enabling --es.use-aliases.

This is a follow-up task to this PR review comment.

Proposal - what do you suggest to solve the problem or improve the existing situation?

The proposal is to add validation at the top of each ES reader and writer constructor with the following logic:

if cfg.GetUseILM() && !cfg.GetUseReadWriteAliases() {
	return nil, fmt.Errorf("the error message")
}

[bhiravabhatla]

Will pick this up

[bhiravabhatla]

Error message could be (from description) - "--es.use-ilm must always be used in conjunction with --es.use-aliases to ensure ES writers and readers refer to the single index mapping"?

[yurishkuro]

+1