-----Original Message-----
From: Christopher Schultz [mailto:ch...@christopherschultz.net]
Sent: Thursday, May 05, 2016 4:26 PM
To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: BackupManager Heterogeneous Environment / Functionality?
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Richard,
On 5/5/16 3:29 PM, Decker, Richard M wrote:
> I'm trying to configure & demo an Apache Tomcat [v8] cluster env, that
> supports different apps functioning on different systems.
>
> Basically, I'm trying to setup an environment where an app can be on
> only 1 or 2 (deployed or running) out of the 3 Tomcat systems in the
> cluster. However, this does not seem to work for me, as I can't get
> away from the 404s when Apache HTTPD goes to a random (round robin)
> Tomcat system, that does not have the application (running or
> deployed) on it.
The one thing you forgot to post was your JkMounts from httpd.conf (or
similar). Can you post those? I believe this can be entirely solved with a
slightly more complicated configuration.
Chris,
Thanks for the quick reply. The info you requested is below. The config is
identical (minus machine names) on the 2 apache httpd systems.
[httpd.conf] equivalent - All JkUn/Mounts
<virtualhost *XXX>
# All requests go to tomcattest by default
JkMount /* acttomcattest
# examples:
# Static files in the examples webapp are served by apache
#Alias /examples /tomcat/webapps/examples
# here we serve the generic default page via apache instead of tomcat
JkUnMount / tomcattest
JkUnMount /index.html tomcattest
JkUnMount /logo.gif tomcattest
# Serve gif using httpd
#JkUnMount /*.gif tomcattest
<virtualhost *XXX>
JkMount /status statustest
> This happens with both new & cached sessions. I can bring an entire
> Tomcat system down, and it works as designed, but not for (stopped or
> undeployed) single applications. I'm really not sure how Tomcat and
> Apache are supposed to communicate with each other in this regard; so
> they know what apps are deployed/running on each system. Is this even
> possible?
Yep. You just need to tell your load-balancer about which applications can be
found where.
So you're suggesting that I list every app in the apache/httpd config, or just
those that won't be deployed across the whole (3 system) env? Sound promising
, but problematic of having to restart the Apache service, whenever a change is
made.
> According to the link below, it should work...
>
> http://tomcat.apache.org/tomcat-8.0-doc/config/cluster-manager.html
>
>
>
>
The org.apache.catalina.ha.session.BackupManager also replicates
> deltas but only to one backup node. The location of the backup node is
> known to all nodes in the cluster. It also supports heterogeneous
> deployments, so the manager knows at what locations the web
> application is deployed.
>
> -------------------- Env - Top Down --------------------
>
> [Load Balancer] - (Sticky Sessions) | [HTTPD1] - [HTTPD2] - (Load
> Balanced, Sticky Sessions) | [Tomcat1] - [Tomcat2] - [Tomcat3] -
> (BackupManager)
Okay.
> -------- Config --------
>
> [HTTPD] worker.list=tomcattest, statustest
>
> worker.tomcat1.type=ajp13 worker.tomcat1.host=tomcat1
> worker.tomcat1.port=XXXX #worker.tomcat1.lbfactor=5
>
> worker.tomcat2.type=ajp13 worker.tomcat2.host=tomcat2
> worker.tomcat2.port=XXXX #worker.tomcat2.lbfactor=5
>
> worker.tomcat3.type=ajp13 worker.tomcat3.host=tomcat3
> worker.tomcat3.port=XXXX #worker.tomcat3.lbfactor=5
>
> worker.tomcattest.type=lb
> worker.tomcattest.balance_workers=tomcat1,tomcat2,tomcat3
> worker.tomcattest.sticky_session=True # lb methods: [R]equest,
> [S]ession, [T]raffic, [B]usiness worker.tomcattest.method=R
> worker.statustest.type=status
If you define more than one lb worker, you can do this in a more nuanced way.
For example:
worker.tomcat1.host=tomcat1
worker.tomcat1.port=XXXX
worker.tomcat2.host=tomcat2
worker.tomcat2.port=XXXX
worker.tomcat3.host=tomcat3
worker.tomcat3.port=XXXX
worker.app-a.type=lb
worker.app-a.balance_workers=tomcat1,tomcat2
worker.app-a.sticky_session=True
worker.app-a.type=lb
worker.app-a.balance_workers=tomcat2,tomcat3
worker.app-a.sticky_session=True
Then, in httpd.conf:
JkMount /app-a/* app-a
JkMount /app-b/* app-b
I think I follow you here.
You can just deploy the applications wherever you want them.
Now, how do you deploy them everywhere but then allow one of them to be taken
out of service without taking-down the whole Tomcat instance?
Tomcat app manager - stopping the application. Or removing/deleting/
undeploying the application itself while Tomcat is (hot) running. This will
most likely break the config for Apache <-> Tomcat though?
There are several ways of doing that which I'll summarize, here. Let's start a
new thread if you want to ask about how to do this in further detail.
1. Deploy a ROOT application on each Tomcat node that will return a "failure"
status whenever you request /app-a/* or /app-b/* (etc.).
Maybe the ROOT web application ALWAYS returns an error status.
2. Use the mod_jk status worker to set the activation status of one of the
Tomcat nodes to "DIS" (disabled). This will send requests without a session
identifier to other nodes in the balancer. Set it to "STO"
and it will cause *all* requests to be sent to other nodes.
The first method is more fault-tolerant and lazy, since you don't have to tell
mod_jk when nodes will be going down. The second method is a little more work,
but it also means that you can drain nodes before scheduled maintenance, which
is nice.
Interesting, I will need to research both of those suggestions a bit more, to
understand them better.
Hope that helps,
- -chris
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