Get document API can specify an alias, but will return documents that are not part of that alias (as defined by the filter for that alias)

[ccw-morris]

Create an index and populate it with two documents. Create an aliases with a filter, such that the alias contains one document.

A search using the alias will return one result.
A get document request using the alias can retrieve both documents.

This may confuse users: "why does this document not turn up in my search results", and makes it hard to implement a security model using aliases.

The UidField.loadDocIdAndVersion() method already uses a filter to check whether the document has been deleted. It would be possible to pass in the alias filter, if defined.

[javanna]

The tricky bit here is that the GET api is realtime, as we can either get document by id from lucene or from the transaction log, before the next refresh happens and the newly indexed documents are made searchable.
Filters are part of the search capabilities of elasticsearch, using the search API, which are not applicable to the GET api. In fact we can only get docs by id from the transaction log, we cannot execute queries (or filters) on top of it.
That's why there are cases where the filter associated with an alias might be ignored. We should at least better document those cases.

[javanna]

I would like to know what people think about the following options:

1. optionally index the document taken from the transaction log in an in memory index so that we can execute the filter against it... seems very slow, default would be not do it but could be enabled via setting
2. just document this, explain clearly why it happens, and make it clear that the get api against filtered aliases is not something you want to build a security model around. Move to search api instead, giving up on the real-time aspect, but relying on the guarantee that only documents that match the filter get returned.

I am personally afraid of the complexity and slowness that would be introduced with option 1. Do comment if you have better ideas around this.

[javanna]

We discussed this, we'd rather prefer to reject get requests performed against a filtered alias, given that we cannot provide users the correct answer. If the get request has the realtime flag set to false though, meaning that the document will only be retrieved from the lucene index, we should not ignore the filter within the alias, instead apply it and do return the result. Marking as adoptme.