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From "Gary Feltham" <garyfelt...@gmail.com>
Subject Re: load balancing with controlled failover
Date Thu, 02 Nov 2006 01:52:38 GMT
Hi Rainer/Jim,

Many thanks, just ran a test with mod_jk 1.2.19 and works great by
setting the node to disabled through the JK status manager. From
further reading it appears to be commonly known as "session draining".

Regards,

Gary

From: Jim Jagielski <jim@jaguNET.com>
To: "Tomcat Users List" <users@tomcat.apache.org>
Date: Wed, 1 Nov 2006 11:14:14 -0500
Subject:
This is expected to be added to the proxy
module, but in a way which is more inline with
expectations for a specific proxy server (whether
serving ajp or http or anything else).

On Nov 1, 2006, at 5:39 AM, Rainer Jung wrote:

> Hi Gary,
>
> from my understanding of the code mod_proxy(_balancer) at the
> moment is
> not able to do that. There are status settings "disable" and "stopped"
> one can set, but at the moment disbled and stopped behave the same. I
> didn't really try, but I derive that from looking at the code. This
> holds true for version 2.2.3, the head of branch 2.2 and trunk as
> well.
>
> I remember some mail on httpd-dev, that this is known and will be
> corrected.
>
> The module mod_jk also has the concept of disable and stop. For mod_jk
> disable means, that requests with sessions on a disabled target still
> get routed there, but requests without a session do not get routed
> to a
> disabled target. So if your sessions are relatively short, you can
> considerably decrease the number of remaining sessions on a target by
> disabling it some time before your maintenance.
>
> I'm sure, this behaviour will come to mod_proxy too, but it looks like
> it's not there yet. Anybody: please correct me if I'm wrong.
>
> If you are going to use mod_jk, please get the latest release 1.2.19.
> It's important to know, that mod_jk can only handle ajp backends.
>
> Regards
>
> Gary Feltham schrieb:
>> Hi,
>>
>> I have a load balancing setup using Apache 2.2.2 (Win32) and 2
>> instances of Tomcat 5.5.15 and 5.5.17. So far I have been able to
>> establish a successful load balancing using sticky sessions with the
>> following config:
>>
>> ProxyPass /test balancer://testcluster stickysession=JSESSIONID
>> nofailover=On
>>
>> <Proxy balancer://testcluster>
>> BalancerMember ajp://127.0.0.1:18009/test smax=5 route=node01
>> BalancerMember ajp://127.0.0.1:28009/test smax=5 route=node02
>> </Proxy>
>>
>> I am not wanting to setup a tomcat cluster for this deployment but
>> have 2 independant instances of tomcat running independant sessions.
>> Currently this is also setup to not failover if an instance goes
>> down.
>> For instance node01 is shutdown, the status is:
>>
>> LoadBalancer Status for balancer://testcluster
>> StickySession   Timeout FailoverAttempts        Method
>> JSESSIONID      0       1       byrequests
>>
>> Worker URL      Route   RouteRedir      Factor  Status
>> ajp://127.0.0.1:18009/test      node01          1       Err
>> ajp://127.0.0.1:28009/test      node02          1       Ok
>>
>> All expected and a request to node 1 results in a 503 response.
>>
>> My question therefore is:
>>
>> Within the context of a scheduled down time such as redeployment of
>> the application or reboot of the server I would like to be able to
>> control closure of the load balancer. For example, node 1 is targeted
>> to be shutdown for maintenance, currently I have 10 user sessions on
>> that instance and say 9 on node 2. If new users join then the load
>> balancer will evenly distribute to each node per request. What I want
>> to control is that each NEW user should only go to node 2, then each
>> session on node 1 will expire eventually leaving 0 sessions on
>> node 1.
>> Node 1 can then be removed cleanly for maintenance and its status set
>> as disabled.
>>
>> Is there a current method of performing this in either mod_proxy or
>> mod_jk - I don't mind which but would like to gain that control?
>>
>> Many thanks,
>>
>> Gary Feltham
>>
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