In AWS OpenSearch, externally hosted models cannot have private IP addresses

[jaxondk]

What is the bug?
In AWS OpenSearch, externally hosted models cannot have private IP addresses. In other (non-AWS) deployments of OS they can (see PR #2534)

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Go to the dev tools on the dashboard of an instance of AWS OpenSearch
2. Run the PUT command for enabling private ip (see here).
3. See error: Your request: '/_cluster/settings' payload is not allowed." flash briefly on the output side of dev tools. Then the screen reloads. No settings are updated.

What is the expected behavior?
I expected to have the settings updated to allow private IP addresses for externally hosted models.

What is your host/environment?
AWS OpenSearch cluster running on 2.15 (also confirmed on 2.19)

Do you have any screenshots?
N/A

Do you have any additional context?
Some context from the original issue for private IP addresses:

@holdenma , sorry that this setting not supported on AWS. Suggest to deploy your model somewhere else like Sagemaker, EC2 etc. You can create load balancer and use that URL in connector.

However, I believe this would cause us to ultimately arrive at the same issue, as @brycecf observed:

@ylwu-amzn Could you elaborate a bit on this? As written, it seems to either arrive at the same issue, if the load balancer also has a private IP, or forces you to introduce a load balancer that has a public IP.

Overall, this issue is a blocker for us to use OpenSearch in our environment.

[ylwu-amzn]

@jaxondk , can we have quick call to understand your requirement details? You can join OpenSearch Slack https://join.slack.com/t/opensearch/shared_invite/zt-378nf6r44-TDOk55qP1mXkpZ_TDEw27A, You can find me in #ml slack channel

[jaxondk]

Sounds good; some other tasking has come up but I'll be circling back to this in about 2 week's time.