[FEATURE] Support HTTP/2

[arunx2]

Is your feature request related to a problem?

No

What solution would you like?

As the opensearch-java library requires Java 11, we can support HTTP/2 as it is much faster and more reliable than HTTP1. HTTP1 loads a single request for every TCP connection, while HTTP2 avoids network delay by using multiplexing. We can either leverage java HttpClient or square's OkHttp libraries

[reta]

@arunx2 see please opensearch-project/OpenSearch#4257

[dblock]

What changes do we need to do in this library after the above was merged? @arunx2 want to contribute? At the least we need to document how to enable HTTP/2.

[reta]

What changes do we need to do in this library after the above was merged?

We basically need to introduce HTTP/2 compatible client transports, there are few ways we could approach that:

• Migrate client transports to Apache HttpClient / Core 5.x - we that, we would get RestClient / RestHighLevelClient with HTTP/1.1 and HTTP/2 support out of the box
• Introduce another implementation of the OpenSearchTransport (using fe Java's standard HttpClient)

Thanks.

[dblock]

What do you think we should do @reta ?

[reta]

@dblock we could do both :-) I aimed to take on Apache HttpClient 5.x but we could also do PoC on dedicated OpenSearchTransport - those are very independent developments. From the bigger picture, I think Apache HttpClient 5.x has better value propostion since it will cover all supported OpenSearch clients, whereas OpenSearchTransport is limited to opensearch-java only

[wbeckler]

@reta what do you mean by "all supported OpenSearch clients." I would propose that opensearch-java be the only "supported" java client.

[reta]

@wbeckler apologies for confusion, there are 3 clients right now: RestClient, RestHighLevelClient and opensearch-java. I think what we want is to have OpenSearch and opensearch-java to live independent lives (no inter-dependencies in other words). That leaves us with: RestClient stays (to be used in core internally), RestHighLevelClient is deprecated (and hopefully removed), opensearch-java becomes the official way to connect to OpenSearch clusters from JVM applications.

[reta]

@dblock @wbeckler I think we could close this one: in 3.0.0 HTTP/2 is already supported (except AWS transport since it is based on Apache HttpClient 4.x).

[dblock]

How about adding in README that this client supports HTTP/2, possibly a section in USER_GUIDE that explains how to use it (does it need to be turned on? does it just work?), and then closing this?

[reta]

Documenting the HTTP/2 support with respect to opensearch-project/OpenSearch#4257