我不明白为什么人们会给他反对票，问题很简单，弹性搜索的文档也不容易理解！

不管怎样，这是解决办法：

class SomeClass
{
    /** @var \Elasticsearch\Client */
    private $client;

    /**
     * @param \Elasticsearch\Client $client
     */
    public function __construct(\Elasticsearch\Client $client)
    {
        $this->client = $client;
    }

    /**
     * @param string $aliasName
     *
     * @return null|string
     */
    public function findIndexNameByAlias($aliasName)
    {
        $aliases = $this->client->indices()->getAliases();
        foreach ($aliases as $index => $aliasMapping) {
            if (array_key_exists($aliasName, $aliasMapping['aliases'])) {
                return $index;
            }
        }

        return null;
    }
}

$someClass = new SomeClass(new \Elasticsearch\Client());
echo "Index associated with 'MyAlias': " . $someClass->findIndexNameByAlias('MyAlias');