The SimpleConnectionPool simply returns the next node as specified by the Selector; it does not perform track the "liveness" of nodes. This pool will return nodes whether they are alive or dead. It is just a simple pool of static hosts.

The SimpleConnectionPool is not recommended for routine use, but it may be a useful debugging tool.

To use the SimpleConnectionPool:

$client = ClientBuilder::create()
            ->setConnectionPool('\Elasticsearch\ConnectionPool\SimpleConnectionPool', [])
            ->build();

Note that the implementation is specified via a namespace path to the class.