使用PHP Couchbase客户端打开存储桶错误

I have a couchbase 3.0.1 installtion on my 64bit Centos vps. I have installed a nginx server with php-fpm. I already have installed C sdk and php sdk. When i want to open a bucket, it return a 'Generic network failure' error.

my code is:

<?php
$myCluster = new CouchbaseCluster('couchbase://localhost');
$myBucket = $myCluster->openBucket('Messenger','password');
?>

Stack trace:

0 [CouchbaseNative]/CouchbaseBucket.class.php(74):
  _CouchbaseBucket->__construct('couchbase://loc...', 'Messenger', 'password') 
1 [CouchbaseNative]/CouchbaseCluster.class.php(61):
  CouchbaseBucket->__construct('couchbase://loc...', 'Messenger', 'password')
2 /usr/share/nginx/html/cb.php(5):
  CouchbaseCluster->openBucket('Messenger', 'password') 
3 {main} thrown in [CouchbaseNative]/CouchbaseBucket.class.php on line 74