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Load balancing and DNS RR

JoePriest
Regular Member

Load balancing and DNS RR

We decided to use DNS Round Robin to "load balance" our Windchill cluster when we went live about 2 years ago. We understood the risks in that it's not supported by PTC Tech Support but management decided that it was worth it in light of the expense of true hardware based load balancers. That being said, we are experiencing an issue now with testing IE 8 that we believe is directly related to the use of DNS RR and the users' session affinity not being maintained.


How are you guys handling your load balancing for those of you who have clusters? Do you use hardware based devices or DNS RR?


Thanks.


Joe

7 REPLIES 7

Load balancing and DNS RR

DNS RR is essentially guaranteed to fail in a Windchill cluster since
Windchill /needs/ session affinity.

Load balancing and DNS RR

You may have simply not needed session data to be preserved in your
particular use cases or perhaps your DNS RR was sufficiently "sticky" in
practice with IE 7 that you ended up with some level of affinity.

In the end, DNS RR cannot be a fully robust solution because it does not
ensure session affinity, whereas the product requires it.

Load balancing and DNS RR

Which would explain IE 7 possibly being sufficiently "sticky" to avoid
issues and IE 8 possibly not being so -- right?

Load balancing and DNS RR

I could also see a terminology issue here without see a specific
configuration one saying something is possible or working when the other
says it doesn't. Session affinity as I understand is managed in Tomcat, a
system with multiple tomcats can safely handle load, not sure I see DNS RR
providing any benefit? Are we thinking multiple apache web servers with
DNS RR? The hardware can conduct the RR but something still has to listen
to that DNS address, is that Apache? Maybe I am also showing my ignorance
on this topic.



- Dave






Load balancing and DNS RR

Session affinity isn't managed by Tomcat -- it's managed by any/all
layers that distribute load between Tomcats. The requirement being that
once a session is established with a given Tomcat that all subsequent
requests within that session end up at that same Tomcat.

If you have a cluster, then the load balancer for your cluster is
responsible for this at this level, i.e. getting requests within a
particular session back to the right cluster node / web server.

If you have multiple Tomcats behind one Apache then mod_jk/mod_proxy_ajp
is responsible for ensuring session affinity at this level, i.e. getting
requests within a particular session back to the right Tomcat amongst
those behind that web server.

--
Jess Holle

Load balancing and DNS RR

Hi Joe,

Please refer below link. We have applied the below load balancer called Pen.
It is very easy to setup and maintain and takes very low resources to work.
The Primary reason we preferred it since it is very good at maintaining
sticky sesions.

Load balancing and DNS RR

Hello Joe,

In our case we are using a software load balancer :
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