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List:       apache-httpd-bugs
Subject:    [Bug 60948] New: Large TCP timeout delays hcheck disabling a node
From:       bugzilla () apache ! org
Date:       2017-03-31 14:59:41
Message-ID: bug-60948-7868 () https ! bz ! apache ! org/bugzilla/
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https://bz.apache.org/bugzilla/show_bug.cgi?id=60948

            Bug ID: 60948
           Summary: Large TCP timeout delays hcheck disabling a node
           Product: Apache httpd-2
           Version: 2.4.25
          Hardware: Sun
                OS: Solaris
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: mod_proxy_hcheck
          Assignee: bugs@httpd.apache.org
          Reporter: michael.renz@kordoba.de
  Target Milestone: ---

Created attachment 34892
  --> https://bz.apache.org/bugzilla/attachment.cgi?id=34892&action=edit
added new hcconnectiontimeout parameter

Using latest patched mod_proxy_hcheck (with patch from bug 60071) I encountered
a problematic situation. 
If a node goes down due to a complete failure and is not reachable via tcp/ip
anymore, the long solaris tcp/ip timeout causes mod_proxy_hcheck to DISABLE the
node very late. 
mod_proxy_hcheck does not provide a connection-timeout parameter to shorten
this.
On top, the threadpool defined via ProxyHCTPsize quickly fills up and uses all
available threads waiting for the timeout. The workaround is to increase
ProxyHCTPsize to e.g. 500. But the problem remains, that once the node goes
down it is not DISABLED until the first timeout has been reached. Solaris has a
timeout of about 120s, therefore the problematic node will still get requests
during this time. These requests will run into the "connectiontimeout", but
this is still not a good situation as it slows down many requests.

I have patched (well, more copy/paste) the mod_proxy_hcheck.c and added a new
parameter called "hcconnectiontimeout". With this new parameter my tests look
good now.
Example configuration would look like this:

   SSLProxyEngine On
   SSLProxyVerify none
   SSLProxyCheckPeerCN off
   SSLProxyCheckPeerName off
   SSLProxyCheckPeerExpire off

   ProxyHCTPsize 400
   ProxyHCExpr get {hc('body') =~ /OK/}
   ProxyHCTemplate server hcmethod=GET hcexpr=get hcfails=1 hcinterval=2
hcpasses=1 hcuri=/tester
   <Proxy balancer://group>
      BalancerMember https://192.168.0.2:8080 connectiontimeout=1
hcconnectiontimeout=1 hctemplate=server
      BalancerMember https://192.168.0.3:8080 connectiontimeout=1
hcconnectiontimeout=1 hctemplate=server
   </Proxy>
<VirtualHost *:80>

   ProxyPass "/" "balancer://group/" failontimeout=On timeout=2
   ProxyPassReverse "/" "balancer://group/"

</VirtualHost>

I hope this helps anyone.

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