对同一服务器的卷曲请求间歇性地超时

I have developed a proxy service in php which uses php-curl to request another url on the same server. Some times it works great but other times it takes a really long time and a lot of the time it times out.

This application does not make use of sessions so it can't be a locked session issue. I tried session_write_close() as a test before calling curl_exec and it made no difference.

What is the cause of this inconsistent behavior? I expect it to respond immediately since the only work it is doing is serving up 302 redirects. I have pasted my proxy function below.

protected function proxy( $pURL,  $opts = array() ){

    $defaults = array(
        'headers' => array(),
        'follow' => true,
        'return' => false,
        'return_headers' => false,
        'referer' => fp_get_config( 'referer_override' ),
        'user_agent' => $_SERVER['HTTP_USER_AGENT'],
        'timeout' => 30,
        'connect_timeout' => 10,
        'fresh_connect' => false
    );

    $options = array_merge( $defaults, $opts );

    extract( $options );

    $c = curl_init( $pURL );

    curl_setopt_array( $c, array(
        CURLOPT_HEADER => $return_headers,
        CURLOPT_USERAGENT => $user_agent,
        CURLOPT_REFERER => $referer,
        CURLOPT_CONNECTTIMEOUT => $connect_timeout,
        CURLOPT_TIMEOUT => $timeout,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_FOLLOWLOCATION => $follow,
        CURLOPT_HTTPHEADER => $headers,
        CURLOPT_FRESH_CONNECT => $fresh_connect,
        CURLOPT_AUTOREFERER => true
    ));

    //session_write_close();

    $response = curl_exec( $c );

    if ( $response === false )
        die("Proxy Error: " . curl_error( $c ) );


    curl_close( $c );

    if ( $return )
        return $response;
    else {

        if ( $return_headers ){

            list( $headerblock, $body ) = explode("

", $response, 2);
            $headers = explode("
", $headerblock );

            foreach( $headers as $header )
                header( $header );

            echo $body;

        } else
            echo $response;
    }

    exit;

}

Turns out what was happening was this: We have two load balancers configured for high availability. Whenever one lb made a curl request to the other lb it was getting blocked by the firewall which caused the connection to timeout. Fixing the firewall rules resolved this issue.