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Subject [Bug 56151] New: mod_proxy sometimes returns 503 errors
Date Tue, 18 Feb 2014 12:11:02 GMT

            Bug ID: 56151
           Summary: mod_proxy sometimes returns 503 errors
           Product: Apache httpd-2
           Version: 2.2.15
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: mod_proxy

Hi there, 

We are running a high volume web application that uses Apache 2.2.15 mod_proxy 
to reverse proxy content from apache to JBoss 6. 

We found 503 errors which happen sporadically throughout the day on random
requests (perhaps 1/2% of daily requests).

Proxy config:

    <IfModule mod_ssl.c>
       <IfModule mod_proxy_http.c>
          ProxyTimeout     600
          SetEnv force-proxy-request-1.0 1
          SetEnv proxy-nokeepalive 1
          ProxyPass        /unproxied/ !
          ProxyPass        /error/ !
          ProxyPass        / retry=0 ttl=600
          ProxyPassReverse /

JBoss config: 

            address              = "${jboss.bind.address}"
            port                 = "8080"
            maxThreads           = "200"
            acceptCount          = "100"
            scheme               = "https"
            secure               = "true"
            proxyName            = "xxx"
            proxyPort            = "443"
            xpoweredBy           = "true"
            connectionTimeout    = "1200000"
            enableLookups        = "false"
            maxKeepAliveRequests = "-1"
            maxHttpHeaderSize    = "50000"
            compression          = "force"
            compressionMinSize   = "512"
            compressableMimeType =

What we can see in the error log:

[Tue Feb 18 10:11:05 2014] [error] (110)Connection timed out: proxy: HTTP:
attempt to connect to ( failed
[Tue Feb 18 10:11:05 2014] [error] ap_proxy_connect_backend disabling worker
for (

What se can see in the access log: 

[18/Feb/2014:10:11:07 +0100] "HEAD /xxx HTTP/1.1" 503 - "https://xxx"
"Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko"

Nothing appears in the JBoss log. 

In the kernel log, we see that every error coincide with an invalid tcp packet: 

kernel: invalid:IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00
SRC= DST= LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=33082 DF
PROTO=TCP SPT=48340 DPT=8080 WINDOW=32792 RES=0x00 SYN URGP=0

After some investigations, this SYN packet is not acknowledged by JBoss in
order to perform the TCP 3-Way Handshake.

I don't know if this is related.

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