It appears that when mod_proxy_balancer is retrying to sent a request to the same worker it drops the POST data and adds itself again to the relevant x-forwarded headers: first request (has been modified for security reasons): [18 Nov 2009 12:16:30,683] POST /integration-server/terminals/2/103/transactions HTTP/1.0 Host: a.tyro.com User-Agent: changed Accept: */* Content-Type: application/x-www-form-urlencoded Expect: 100-continue X-Forwarded-For: A.B.C.D X-Forwarded-Host: a.tyro.com X-Forwarded-Server: a.tyro.com Content-Length: 154 second request (has been modified for security reasons): [18 Nov 2009 12:16:30,690] POST /integration-server/terminals/2/103/transactions HTTP/1.0 Host: a.tyro.com User-Agent: changed Accept: */* Content-Type: application/x-www-form-urlencoded Expect: 100-continue X-Forwarded-For: 59.167.235.179, 59.167.235.179 X-Forwarded-Host: a.tyro.com, a.tyro.com X-Forwarded-Server: a.tyro.com, a.tyro.com Content-Length: 0 This is a reproducible behaviour. Does that make sense to anyone who knows the code? Also just to confuse me a little bit more: Our application servers responded with a 503 and it looked like the balancer is retrying the connection instead of passing this on to the client? I did some reading and thought that the balancer only considers a connection problem to the worker a failover reason? Our configuration is: [...] SetEnv force-proxy-request-1.0 1 SetEnv proxy-nokeepalive 1 <Proxy balancer://integrationwebapp> BalancerMember http://webapp-1:8008 retry=60 BalancerMember http://webapp-2:8008 status=+H ProxySet lbmethod=bytraffic </Proxy> [...] //sascha
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