src/Index/AliasProcessor.php
public function setRootName(IndexConfig $indexConfig, Index $index)
    {
        $index->overrideName(
            sprintf('%s_%s',
                $indexConfig->getElasticSearchName(),
                date('Y-m-d-His')
            )
        );
    }
public function setRootName(IndexConfig $indexConfig, Index $index)
    {
        $index->overrideName(
            sprintf('%s_%s',
                $indexConfig->getElasticSearchName(),
                date('Y-m-d-His')
            )
        );
    }
Sets the randomised root name for an index.

@param IndexConfig $indexConfig
@param Index       $index