in elasticsearch/src/http/transport.rs [998:1005]
fn try_next(&self, connections: &[Connection]) -> Result<Connection, Error> {
if connections.is_empty() {
Err(crate::error::lib("Connection list empty"))
} else {
let i = self.index.fetch_add(1, Ordering::Relaxed) % connections.len();
Ok(connections[i].clone())
}
}