With _type removal in OpenSearch 2.0+ (previously deprecated in Elasticsearch 7.x); beat still uses _type as DocType while building BulkRequest meta data; resulting in illegal_argument_exception from OpenSearch engine.
Exception to end user
400 Bad Request: {"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"Action/metadata line [1] contains an unknown parameter [_type]"}],"type":"illegal_argument_exception","reason":"Action/metadata line [1] contains an unknown parameter [_type]"},"status":400}
BulkMeta in beat
type BulkMeta struct {
Index string `json:"_index" struct:"_index"`
DocType string `json:"_type,omitempty" struct:"_type,omitempty"`
Pipeline string `json:"pipeline,omitempty" struct:"pipeline,omitempty"`
ID string `json:"_id,omitempty" struct:"_id,omitempty"`
}