Verify Usage of Opensearch Core System and Hidden Indices

[Rishikesh1159]

Description/Concept of System Indices and Hidden Indices on Opensearch core:

System Index - An index must extend system index plugin for a index to be called as system index.
Example: Security Plugin correctly extends and uses system Indices, more info here

Hidden index - An index must have hidden SETTING_INDEX_HIDDEN = "index.hidden" set on the index setting to call it as hidden. It doesn't matter if it starts with "." or not.
Example: Asynchronous-Search plugin correctly sets the index setting value here

Misconception:

Many plugins still misunderstand the actual definition of system and hidden indices. Usual misconception is that any index starting with . like .indexName is a system or hidden index, but this is incorrect. Any user can create an index with .indexName which is neither a system or hidden index. So users can mistakenly still create index starting with "." there is nothing stopping them from doing it.

To avoid this misconception all plugins should adopt/on-board with concept of system and hidden indices defined in opensearch core.

Goal:

The main ask of this issue is to make sure all plugins having/using system and hidden indices must on-board/adopt with concept defined in opensearch core.

Any plugin already on-board with opensearch core defined concept of system and hidden indices can ignore this issue and close the issue as completed on the plugin repo.

Additional info:

The following info provided below is not necessary for system/hidden indices, but might be useful info for plugins using system indices :

If your system indices need additonal security features/benefits provided by security plugin, follow the steps provided here. But to make sure these are additonal features provided by security plugin and it is completely decoupled from concept of system indices. It is upto the plugin owners to decide if they need these additional security benefits.

Open questions

In case of any questions or issues, please post it in core issue

[jmazanec15]

For k-NN:

1. system index: https://github.com/opensearch-project/k-NN/blob/main/src/main/java/org/opensearch/knn/plugin/KNNPlugin.java#L341
2. hidden index: https://github.com/opensearch-project/k-NN/blob/main/src/main/java/org/opensearch/knn/indices/ModelDao.java#L227

Think we are good on this. Closing