Index aliases are one of the most underappreciated features in ES. In general, when building an app that uses ES I’d recommend to always hide the actual index behind an alias. There’s a minor error in the post: you can write to an alias, but only if it points to exactly one index. By using an alias to read and write, the actual index is hidden from the app. This allows tweaking indices and doing test runs on two indices with different mappings/settings by modifying the alias. Especially when doing performance or scoring optimizations, this can massively improve your agility when testing such a change.