I am looking for some guidance on using HTTPD as a proxy and load balancer
to a backend Tomcat application.  Specifically, I'm interested in how to
best handle the balancing of requests.  The configuration would be very
much like the 'typical implementation' shown in this Reverse Proxy Guide:  (I'm using
version 2.4.6):

+---------------------  +
|     Firewall Public |
+---------------------  +
|      +------+   +-------+  +-------+      |
|      | httpd|   | httpd  |   | httpd |      |
|      |    1   |   |   2      |   |   3     |      |
|      +------+   +-------+  +-------+      |
+----------------------  +
|     Firewall Private |
+----------------------  +
|    +--------+  +---------+  +--------+      |
|    | tomcat|  |tomcat |   |tomcat |       |
|    |   1       |  |    2      |   |   3       |      |
|    +--------+  +---------+  +--------+      |

We have this working fine with a vanity URL to a VIP on our public firewall
--> to the 3 httpd proxy load balancer pool --> to one of the 3 backend
Tomcat server pool.  We want everything to run over SSL and the currently
working config on the httpd servers is basic:

<VirtualHost _default_:443>


        SSLEngine on
        SSLProtocol all -SSLv2 -SSLv3
        SSLCipherSuite HIGH:MEDIUM:!aNULL:!MD5:!SEED:!IDEA

        SSLCertificateFile /etc/pki/tls/certs/ssl.crt

# ------------------------------------------------
# Proxy Load Balancer
# ------------------------------------------------

<Proxy balancer://mycluster>



SSLProxyEngine on
SSLProxyVerify none
SSLProxyCheckPeerCN off
SSLProxyCheckPeerName off
SSLProxyCheckPeerExpire off

ProxyPass / balancer://mycluster/
ProxyPassReverse / balancer://mycluster/


As mentioned, this works fine.  But now we need to dig into the request
management.  I read here:
2.4/mod/mod_proxy_balancer.html that the scheduler algorithm is provided by
'at least one of':



1. Am I correct in reading 'at least one of' that multiple of these
algorithms can be used together?  If so, is there a hierarchy between them?

2. Does it make sense to use multiple algorithms?

- It sounds like each could be desirable:
mod_lbmethod_byrequests -> We do want to have an even distribution of

mod_lbmethod_bytraffic -> Some requests/sessions could be more intensive
than others.

mod_lbmethod_bybusyness -> Sounds similar to byrequests?

mod_lbmethod_heartbeat -> Definately need to backend to be listening but
would be nice to distribute or overlook a server based upon response time.
Is that part of how this works?

3. Is using HTTPD mod_proxy_balancer the best way to handle what we are
looking to do?  Or are there better options?

4. On the backend we plan on using Tomcat session clustering for high
availability.  That being the case, would that mean that we would NOT want
to use sticky sessions at the HTTPD level in case a backend Tomcat node
goes offline and the session is picked up on one of the other nodes?

Sorry if I've confused anything here, any guidance is greatly appreciated.
I'm happy to read any documentation directed to..

Thanks in advance,


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