This Elastica transport class allows CirrusSearch to work with elasticsearch 6.8.23 while using ruflin/Elastica 7.1.5. It can be enabled like this:

$wgCirrusSearchClusters = [
        [
                'transport' => [
                        "type" => \CirrusSearch\Elastica\ES6CompatTransportWrapper::class,
                        'wrapped_transport' => 'Http'
                ],
                "port" => 9200,
                "host" => "elasticsearch_hostname"
        ]
];

This mainly allows writes to be properly applied. It was used on the WMF infrastucture to allow a zero-downtime upgrade migration plan. It is strongly advised to upgrade to elasticsearch 7.10.2 rather than using this compatibility layer.