mod_proxy与mod_rewrite结合时报"DNS lookup failure"错误

通过mod_rewrite修改url，并将url传给后台的多个应用服务器，利用mod_proxy做负载均衡。下面是配置：

<VirtualHost *:1380>
    ServerName www.mysite.com
   
    AddOutputFilterByType DEFLATE text/html text/css application/x-javascript

    ProxyPass /balancer-manager !
    ProxyPass /yui !
    ProxyPass /img !
    ProxyPass /js !
    ProxyPass /css !
    ProxyPass / balancer://jycluster/
    ProxyPassReverse / balancer://jycluster/
    <roxy balancer://jycluster>
        BalancerMember http://127.0.0.1:8080 min=10 smax=15 max=20
        BalancerMember http://127.0.0.1:8081 min=10 smax=15 max=20
    </Proxy>

    RewriteEngine On
    RewriteRule ^/balancer-manager$ /balancer-manager [P,L]
</VirtualHost>

当访问http://www.mysite.com/balancer-manager时，mod_proxy报502错误：
Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /balancer-manager.

Reason: DNS lookup failure for: www.mysite.com

但是如果将配置最后一行"RewriteRule ...”注释掉之后，则可以成功访问http://www.mysite.com/balancer-manager

下面是rewrite的log:
(2) init rewrite engine with requested uri /balancer-manager
(3) applying pattern '^/balancer-manager$' to uri '/balancer-manager'
(2) rewrite '/balancer-manager' -> '/balancer-manager'
(2) forcing proxy-throughput with http://www.mysite.com:1380/balancer-manager
(1) go-ahead with proxy request proxy:http://www.mysite.com:1380/balancer-manager [OK]

平台信息：
Linux 2.6.9
Apache 2.2.8

那位兄台能解释一下为什么会出现DNS lookup的错误呢？我还需要做些什么才能使Apache能顺利运行？

我也是用apache做的反向代理，也出现了你这样的错误，后来我发现是配置错误：
<VirtualHost 10.5.160.174:80>
ServerName 100.15.60.14:80
ProxyPass / http://100.15.20.12:80/   
ProxyPassReverse / http://100.15.20.12:80/
CacheMaxExpire 0.1
CacheLastModifiedFactor 0.1
CacheDefaultExpire 1
</VirtualHost>

ProxyPass / http://100.15.20.12:80/    后面忘了加“/”了，变成了ProxyPass / http://100.15.20.12:80 ，所以引起错误，加上“/”之后就没事了。