The proxy server received an invalid response from an upstream server

Question

We have an application deployed on tomcat  To access application we are using apache which sends requests to tomcat  At random browser gives following response   Proxy Error The proxy server received an invalid response from an upstream server  The proxy server could not handle the request GET  sampleapp  lt http   samplehost com 8080 sampleapp  gt   Reason  Error reading from remote server                                  Apache 2 2 21  Unix  Server at samplehost com Port 8080   This error is not coming always and so far we are getting this in a client machine with IE only  On the same client machine with Firefox it works well   Following is the error trace from Apache logs for a failed request   Thu Mar 22 02 51 08 2012   error   client 10 36 64 137   20014 Internal error  proxy  error reading status line from remote server localhost 8081  referer  http   samplehost com 8080 sampleapp opp showSearchHome htm  Thu Mar 22 02 51 08 2012   error   client 10 36 64 137  proxy  Error reading from remote server returned by  sampleapp opp searchResult htm  referer  http   samplehost com 8080 sampleapp opp showSearchHome htm   Nothing is getting printed on tomcat logs when a request is failing   Following is the information related installed version of apache  -bash-3 00    httpd -v Server version  Apache 2 2 21  Unix  Server built    Sep 21 2011 20 00 58   When trying to find out modules loaded I get following error  -bash-3 00   usr local apache2 bin apachectl -t -D DUMP MODULES httpd  Syntax error on line 64 of  usr local apache2 conf httpd conf  Cannot load  usr local apache2 modules mod authnz ldap so into server  ld so 1  httpd  fatal  libldap-2 4 so 2  open failed  No such file or directory

User · Accepted Answer

This is not mentioned in you post but I suspect you are initiating an SSL connection from the browser to Apache, where VirtualHosts are configured, and Apache does a revese proxy to your Tomcat.

There is a serious bug in (some versions ?) of IE that sends the 'wrong' host information in an SSL connection (see EDIT below) and confuses the Apache VirtualHosts. In short the server name presented is the one of the reverse DNS resolution of the IP, not the one in the URL.

The workaround is to have one IP address per SSL virtual hosts/server name. Is short, you must end up with something like

1 server name == 1 IP address == 1 certificate == 1 Apache Virtual Host

EDIT

Though the conclusion is correct, the identification of the problem is better described here http://en.wikipedia.org/wiki/Server_Name_Indication

[apache] The proxy server received an invalid response from an upstream server

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