[FEATURE] Add support for OpenSearch Serverless

[dblock]

Is your feature request related to a problem?

• OpenSearch serverless service identifier changes from es to aoss
• Sigv4 requires a hash

What solution would you like?

Document support for OpenSearch Serverless in the compatibility matrix, add integration tests.

Do you have any additional context?

Coming from opensearch-project/opensearch-clients#44

[wbeckler]

I modified the issue to delay addressing the API incompatibilities

[wbeckler]

This is doable today with the following invocation style:

from opensearchpy import OpenSearch, RequestsHttpConnection
from requests_aws4auth import AWS4Auth
import boto3

host = '' # The collection endpoint without https://. For example, 07tjusf2h91cunochc.us-east-1.aoss.amazonaws.com
region = '' # e.g. us-east-1

service = 'aoss'
credentials = boto3.Session().get_credentials()
awsauth = AWS4Auth(credentials.access_key, credentials.secret_key, region, service, session_token=credentials.token)

# Build the OpenSearch client
client = OpenSearch(
    hosts = [{'host': host, 'port': 443}],
    http_auth = awsauth,
    use_ssl = True,
    verify_certs = True,
    connection_class = RequestsHttpConnection
)

# Create an index
index_name = 'my-index'
index_body = {
    "mappings": {
        "properties": {
            "title": {"type": "text"},
            "director": {"type": "text"},
            "year": {"type": "integer"}
        }
    }
}
response = client.indices.create(index_name, body=index_body)
print('\nCreating index:')
print(response)

The question is, is it better to incorporate this logic into AWSV4SignerAuth? The downside is that it would make something opaque and magical that is relatively straightforward.

[wbeckler]

@dblock thoughts?

[wbeckler]

Also, what's a good strategy for doing an integration test for this?

[wbeckler]

And, is it possible that someone could make it unnecessary to specify a service name and that the client would try aoss and es and it would find one that works?

[dblock]

I think the code that a developer has to write to talk to Managed OpenSearch should be identical to OpenSearch Serverless minus the service name. This looks like a good current workaround, but I definitely think we want to expose service name in AWSV4SignerAuth. I certainly agree that we don't want anything magical like the client trying aoss vs. es, especially because it would hide failing HTTP requests - let the caller specify.