How to issue POST requests to opensearch cluster in VPC?

Question

I've deployed an opensearch cluster into a VPC. I have a VPC endpoint and can successfully issue GET requests to "VPC endpoint URL"/_cluster/settings to get the cluster config, but issuing POST requests to the same URL does not work. Should issuing POST requests to "VPC endpoint URL"/_cluster/settings work?

Looking at the documentation - https://docs.aws.amazon.com/opensearch-service/latest/developerguide/configuration-api.html#configuration-api-actions-describedomainconfig - it says to -

POST https://es.us-east-1.amazonaws.com/2021-01-01/opensearch/domain/domain-name/config
"SnapshotOptions": {
    "AutomatedSnapshotStartHour": 3
  }

Since that is a public URL, I can't do that with my cluster. I also tried a POST request to "VPC endpoint URL"/config without any luck.

My working GET request -

def lambda_handler(event, context):
    x = requests.get('https://vpc-<private endpoint>.us-east-1.es.amazonaws.com/_cluster/settings')

Successful output from GET request -

Function Logs
:"5s","max_index_buffer_size":"-1","shard_inactive_time":"5m",...

My failing POST request -

def lambda_handler(event, context):
    url = 'https://vpc-<private endpoint>.us-east-1.es.amazonaws.com/_cluster/settings'
    myobj = {"SnapshotOptions": {
    "AutomatedSnapshotStartHour": 3
  } }
    x = requests.post(url, json = myobj)

Error Message -

Function Logs
START RequestId: b483f2ca-0051-468a-81cf-8a771a667bd2 Version: $LATEST
{"Message":"Your request: '/_cluster/settings' is not allowed for verb: POST"}

Answer 1

The resolution I discovered was signing the request. - https://docs.aws.amazon.com/opensearch-service/latest/developerguide/request-signing.html

Ex. -

from opensearchpy import OpenSearch, RequestsHttpConnection, AWSV4SignerAuth
import boto3

host = '' # cluster endpoint, for example: my-test-domain.us-east-1.es.amazonaws.com
region = '' # e.g. us-west-1

credentials = boto3.Session().get_credentials()
auth = AWSV4SignerAuth(credentials, region)
index_name = 'movies'

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

q = 'miller'
query = {
  'size': 5,
  'query': {
    'multi_match': {
      'query': q,
      'fields': ['title^2', 'director']
    }
  }
}

response = client.search(
    body = query,
    index = index_name
)

print('\nSearch results:')
print(response)