no address for xxxxx (Resolv::ResolvError)

Hello,

When we are trying to use basic authentication parameters (host/port/user/password) to connect to oss we get connection issue:
2022-02-15 13:41:35 +0000 [debug]: #0 'host_placeholder es_node' is tested built-in placeholder(s) but there is no valid placeholder(s). error: Parameter 'host_placeholder: es_node' doesn't have tag placeholder
2022-02-15 13:41:37 +0000 [warn]: #0 Could not communicate to OpenSearch, resetting connection and trying again. no address for es_node (Resolv::ResolvError)

#### Steps to replicate

1. In OpenSearch we use HTTP Basic Auth Policy which includes:
- Domain access policy is set to "Allow Open Access to the domain"
- fine-grain control enabled and master user is set from internal user database, special user (admin) for fluentd-plugin-opensearch is created with proper OpenSearch role.
2. Open-search plugin settings

@type opensearch
@log_level debug
host "es_node"
port 9200
user "admin"
password xxxxxx
scheme http
logstash_format true
include_tag_key true
request_timeout 20s

@type file
path /opt/bitnami/fluentd/logs/buffers/logs.buffer
flush_interval 5s
flush_thread_count 8
chunk_limit_size 2M
queue_limit_length 32
retry_max_interval 30
retry_forever true

#### Expected Behavior or What you need to ask
successful connection to OSS.

Is there any way (except: log_level debug) to debug the connection parameters?
'curl' command works fine from the fluentd pod with the same parameters (curl -u 'admin:xxxxxx' http://es_node/)

#### Using Fluentd and OpenSearch plugin versions
env: AWS EKS, in k8s pod
Fluentd version 1.14.4
Opensearch version: OpenDistro oss 7.10.2
'fluent-plugin-opensearch' version '1.0.1'