On 26.08.2010 11:57, michael bienstein wrote:
Hi all. I'm trying to configure a proxy_loadbalancer with sticky
session. I read around the web and in the source code and discovered
that this module expects to handle sticky session by re-using the user's
session ID provided by the origin server. This is different to BigIP
which injects its own cookie that it keeps track of. Apache also expects
the origin server to know it is being load-balanced and to change the
session ID it creates to include a "route" that identifies that origin
server.
So for example if my origin server is Tomcat then the session cookie
would be JSESSIONID=12345... and Tomcat has to be modified to make it
JSESSIONID="12345.route1". Apache mod_proxy_loadbalancer sees this and
finds the route1 and chooses the right origin server based on that. I
also read that PHP doesn't have the possibility of changing the cookie,
but since PHP runs typically on Apache, it is possible to modify the
configuration of the origin server to post-process the request to add it.
My problem is that I load balance a custom web server and/or IIS and we
have neither of these options available. I need the cookie to go through
as originally created and I can't change the way it gets created. So,
how to do it?
I have tried to add a cookie at the proxy server, but I can't get this
to only happen when the origin server sends through its cookie. In fact
if the origin server sends an error code, the environment variable I use
with SetEnvIf isn't set correctly. I can't see how to add a cookie in a
post-processing filter of some sort either. The only ways I see to add
cookies are in mod_rewrite (which seems strange to me) and via mod_headers.
Any ideas?
Have a look at the second example in
http://httpd.apache.org/docs/trunk/mod/mod_proxy_balancer.html#example
It uses the following features:
- Apache itself can also set a cookie
- the value of the cookie can be interpolated from
Apache environment variables that are being set
by the balancer
- setting the cookie can be made dependent on
whether the load balancer set a variable indicating
that the request changed nodes (or wasn't sticky)
All of the ingredients used in this example for Apache trunk (the actual
beta version 2.3) should IMHO be already available in 2.2 (except for
the nice example in the docs).
If you want to track how this works, you can add
%{Set-Cookie}o %{ROUTEID}C %{BALANCER_WORKER_ROUTE}e
%{BALANCER_ROUTE_CHANGED}e
to your LogFormat (Access-Log).
NOTE: I think the first of these config lines should use "Set-Cookie"
instead of "Set-Cookie:".
Regards,
Rainer
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