UnsupportedProductError is raised when connecting to OSS-only Elasticsearch distributions

Elasticsearch version (bin/elasticsearch --version): Using docker.elastic.co/elasticsearch/elasticsearch-oss:7.9.1

elasticsearch-py version (elasticsearch.__versionstr__): 7.14.0a1

Description of the problem including expected versus actual behavior:

The transport _do_verify_elasticsearch function returns false, preventing the use of the elasticsearch API since the transport refuses to talk to ES.

Steps to reproduce:

Start a 7.9.1 docker container

 docker run --rm --name es -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch-oss:7.9.1

Then try connecting to it via the python connector

>>> import elasticsearch
>>> es = elasticsearch.Elasticsearch(hosts='http://localhost:9200/')
>>> es.info()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/user/.pyenv/versions/3.8.10/envs/proj/lib/python3.8/site-packages/elasticsearch/client/utils.py", line 168, in _wrapped
    return func(*args, params=params, headers=headers, **kwargs)
  File "/home/user/.pyenv/versions/3.8.10/envs/proj/lib/python3.8/site-packages/elasticsearch/client/__init__.py", line 294, in info
    return self.transport.perform_request(
  File "/home/user/.pyenv/versions/3.8.10/envs/proj/lib/python3.8/site-packages/elasticsearch/transport.py", line 413, in perform_request
    raise NotElasticsearchError(
elasticsearch.exceptions.NotElasticsearchError: The client noticed that the server is not Elasticsearch and we do not support this unknown product

Logging the args given to _verify_elasticsearch contains the following information

INFO     elasticsearch:base.py:270 GET http://localhost:9200/ [status:200 request:0.003s]
INFO     elasticsearch:transport.py:499 {'content-type': 'application/json; charset=UTF-8', 'content-length': '537'}
INFO     elasticsearch:transport.py:500 {'name': 'df9e379eabf8', 'cluster_name': 'docker-cluster', 'cluster_uuid': 'NMWmEyckTqK2UMKgVM_zCA', 'version': {'number': '7.9.1', 'build_flavor': 'oss', 'build_type': 'docker', 'build_hash': '083627f112ba94dffc1232e8b42b73492789ef91', 'build_date': '2020-09-01T21:22:21.964974Z', 'build_snapshot': False, 'lucene_version': '8.6.2', 'minimum_wire_compatibility_version': '6.8.0', 'minimum_index_compatibility_version': '6.0.0-beta1'}, 'tagline': 'You Know, for Search'}

[philkra]

Thank you for the feedback about the compatibility of the README. We are addressing the wording to mitigate confusion.

Elastic’s recommendation is to upgrade the server first, then the client. Which entails a forward compatible of the language clients. The following paragraph is defined in docs of the HLRC:

The High Level Client is guaranteed to be able to communicate with any Elasticsearch node running on the same major version and greater or equal minor version. It doesn’t need to be in the same minor version as the Elasticsearch nodes it communicates with, as it is forward compatible meaning that it supports communicating with later versions of Elasticsearch than the one it was developed for.

[lnielsen]

We also see the same error when using containers:

~$ curl http://127.0.0.1:9200
{
  "name" : "60865ffac484",
  "cluster_name" : "docker-cluster",
  "cluster_uuid" : "eCYk6HMBSOu9jznjKXipzw",
  "version" : {
    "number" : "7.10.2",
    "build_flavor" : "oss",
    "build_type" : "docker",
    "build_hash" : "747e1cc71def077253878a59143c1f785afa92b9",
    "build_date" : "2021-01-13T00:42:12.435326Z",
    "build_snapshot" : false,
    "lucene_version" : "8.7.0",
    "minimum_wire_compatibility_version" : "6.8.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
  },
  "tagline" : "You Know, for Search"
}