src/Index/AliasProcessor.php
private function getAliasedIndex(Client $client, $aliasName)
    {
        $aliasesInfo = $client->request('_aliases', 'GET')->getData();
        $aliasedIndexes = [];

        foreach ($aliasesInfo as $indexName => $indexInfo) {
            if ($indexName === $aliasName) {
                throw new AliasIsIndexException($indexName);
            }
            if (!isset($indexInfo['aliases'])) {
                continue;
            }

            $aliases = array_keys($indexInfo['aliases']);
            if (in_array($aliasName, $aliases)) {
                $aliasedIndexes[] = $indexName;
            }
        }

        if (count($aliasedIndexes) > 1) {
            throw new \RuntimeException(sprintf(
                'Alias %s is used for multiple indexes: [%s]. Make sure it\'s'.
                'either not used or is assigned to one index only',
                $aliasName,
                implode(', ', $aliasedIndexes)
            ));
        }

        return array_shift($aliasedIndexes);
    }
private function getAliasedIndex(Client $client, $aliasName)
    {
        $aliasesInfo = $client->request('_aliases', 'GET')->getData();
        $aliasedIndexes = [];

        foreach ($aliasesInfo as $indexName => $indexInfo) {
            if ($indexName === $aliasName) {
                throw new AliasIsIndexException($indexName);
            }
            if (!isset($indexInfo['aliases'])) {
                continue;
            }

            $aliases = array_keys($indexInfo['aliases']);
            if (in_array($aliasName, $aliases)) {
                $aliasedIndexes[] = $indexName;
            }
        }

        if (count($aliasedIndexes) > 1) {
            throw new \RuntimeException(sprintf(
                'Alias %s is used for multiple indexes: [%s]. Make sure it\'s'.
                'either not used or is assigned to one index only',
                $aliasName,
                implode(', ', $aliasedIndexes)
            ));
        }

        return array_shift($aliasedIndexes);
    }
Returns the name of a single index that an alias points to or throws
an exception if there is more than one.

@param Client $client
@param string $aliasName Alias name

@return string|null

@throws AliasIsIndexException