php - SSH 连接在重负载下失败

Question

$con = ssh2_connect($host, 22);
ssh2_auth_password($con, $rem_acc, $pass);
ssh2_scp_send($con,$rand.".gz","./".$rand.".gz");
$stream = ssh2_exec($con, "./exeonserv.sh ".$rand);

只要我将 PHP 脚本的负载保持在每秒 2 个请求以下(脚本中有 2 个 SSH 连接，因此每秒有 4 个连接)，就可以正常工作

但是当它每秒超过 2 个请求时，连接开始失败，日志中出现以下错误:

[Sat Apr 21 11:51:40 2012] [error] [client 172.16.57.97] PHP Warning: ssh2_connect(): Error starting up SSH connection(-1): Failed getting banner in /var/www/fsproj/result.php on line 105
[Sat Apr 21 11:51:40 2012] [error] [client 172.16.57.97] PHP Warning: ssh2_connect(): Unable to connect to localhost in /var/www/fsproj/result.php on line 105

我使用以下代码尝试解决问题，但如果持续负载大于 2req/sec。它只是最终增加了响应时间

$con=false;    
while(!$con)
{
    $con = ssh2_connect($host, 22);
}

可以打开 SSH 连接的最大速率是否有上限？如果是这样，我在哪里可以更改该值？ (或任何其他解决方案？)

我在 Ubuntu 上使用 Apache

Answer 1

看看man sshd_config ，以下部分似乎控制了一次可以打开的最大 SSH 连接数以及最大并发连接尝试数。您需要修改 /etc/ssh/sshd_config与您想要的设置。

     MaxSessions
             Specifies the maximum number of open sessions permitted per net-
             work connection.  The default is 10.

     MaxStartups
             Specifies the maximum number of concurrent unauthenticated con-
             nections to the SSH daemon.  Additional connections will be
             dropped until authentication succeeds or the LoginGraceTime
             expires for a connection.  The default is 10.

             Alternatively, random early drop can be enabled by specifying the
             three colon separated values ``start:rate:full'' (e.g.
             "10:30:60").  sshd(8) will refuse connection attempts with a
             probability of ``rate/100'' (30%) if there are currently
             ``start'' (10) unauthenticated connections.  The probability
             increases linearly and all connection attempts are refused if the
             number of unauthenticated connections reaches ``full'' (60).

此外，对于您尝试连接到服务器的示例，您可能需要添加 sleep 连接尝试失败后。如果没有此退避并且服务器被淹没，您的脚本可能会通过尝试通过连接尝试更多地淹没服务器而使事情变得更糟。