使用 ProxyPass 的 Apache httpd 錯誤“代理：ap_get_scoreboard_lb”

我設置了 apache 來代理 tomcat，但是當我定位頁面時出現以下錯誤。我有時會得​​到一個空白頁或 503：

$$ Error $$

[Mon Dec 03 04:58:16 2012] [error] proxy: ap_get_scoreboard_lb(2) failed in child 29611 for worker proxy:reverse
[Mon Dec 03 04:58:16 2012] [error] proxy: ap_get_scoreboard_lb(1) failed in child 29611 for worker https://localhost:8443/
[Mon Dec 03 04:58:16 2012] [error] proxy: ap_get_scoreboard_lb(0) failed in child 29611 for worker http://localhost:8080/

我在 vm 上配置了兩個虛擬主機，如下所示：

$$ http host $$

<VirtualHost *:80>
 ServerName www.mysite.net
 ServerAlias mysite.net

 ProxyRequests Off
 ProxyPreserveHost On

 <Proxy *>
   Order deny,allow
   Allow from all
 </Proxy>

 ProxyPass / http://localhost:8080/ retry=0
 ProxyPassReverse / http://localhost:8080/ retry=0
</VirtualHost>

$$ ssl vhost $$

<VirtualHost *:443>
       ServerName www.mysite.net
       ServerAlias mysite.net

       ErrorLog /var/log/apache2/error.log

       LogLevel warn

       CustomLog /var/log/apache2/access.log combined
       ServerSignature On

       SSLEngine on
       SSLProxyEngine on
       SSLCertificateFile /etc/apache2/ssl/server.crt
       SSLCertificateKeyFile /etc/apache2/ssl/server.key

       ProxyRequests Off
       ProxyPreserveHost On
       ProxyPass / https://localhost:8443/ retry=0
       ProxyPassReverse / https://localhost:8443/ retry=0

</VirtualHost>

我的系統詳細資訊是：Apache/2.2.22 (Ubuntu) mod_jk/1.2.32 mod_ssl/2.2.22 OpenSSL/1.0.1 mod proxy_http 也已啟用。

似乎在停止然後啟動 apache 和apachectl graceful重新啟動（即實際停止和啟動而不是apachectl restart）之間存在差異，如在此站點上找到的：

This is a bit of a guess, and probably wrong, but does stopping and 
starting the server rather than restarting (they're different, 
restarting (including gracefully) doesn't kill the master process) 
help? As I understand it, there are issues in mod_proxy regarding the 
scoreboard size when changes to the config are made between restarts.

引用自：https://serverfault.com/questions/454421