ActiveSync - CAS

ferrarista
ferrarista used Ask the Experts™
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I'm not quite sure how ActiveSync works when working with two load balanced CAS servers.
Do they use the same CAS server for a certain lenght of time ? Or do they costantly talk to either server ?

I was doing a test like refreshing my inbox on the mobile device and I can actually see IIS traffic on both CAS servers. So how does it actually work ? I cannot find any material to explain this. Would love to get an insight.

Thanks so much.
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AkhaterSolutions Architect

Commented:
Depends on your load balancing technology
Solutions Architect
Commented:
If you have a dedicated load balancer it is usually configured to use cookie insert for sticky sessions so one client will connect to one cas server until the cookie expires or the server goes down

If you are using Windows load balancing it is typically random / round robin

Author

Commented:
We are actually using round robin.
What puzzles me is that I find transactions on both servers at basically the same time, so that got me thinking....

I'm actually trying to resolve a problem where EAS performance has suddenly decreased.
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AkhaterSolutions Architect

Commented:
No a connection will happen only to one of the servers at a time
Most Valuable Expert 2014

Commented:
Round Robin isn't load balancing.
If you are seeing problems, then take it out. Ensure all traffic goes to one server.
If you want HA for CAS, then you need a load balancer. Kemp or JetNexus are the most common ones I deploy.

Author

Commented:
Hi, we use NLB,,,very simple load balancer. But I doubt that is the problem.
AkhaterSolutions Architect

Commented:
I'm sorry Simon but Round Robin is load balancing

All load balancers have a RR mode and even DNS round Robin provides Load Balancing. Maybe not HA in the case of 2010 but definitely load balancing in its most basic form
Most Valuable Expert 2014
Commented:
No, round robin is not load balancing.
Round robin has no concept of the load.
DNS round robin has no concept of service availability. If a server goes down then DNS keeps sending traffic to that place.

Windows NLB is not recommended by the Exchange product team for use with Exchange. Get a proper load balancer.

Even so, if any kind of load balancer is involved it has to be bypassed to confirm it is not the cause of the problems. Never presume it is not the cause, because in my experience they usually are, or you cannot do anything until you have shown they are not.
AkhaterSolutions Architect

Commented:
I am aware of all that but since users will be randomly distributed around the servers it is safe to assume that the load will be balanced even though it is a random distribution and not a smart one

The fact that it is not service aware makes it not suitable for high availability (which I said in my previous post)
AkhaterSolutions Architect

Commented:
Btw I'm not arguing with idea to bypass it or that it might be the source of the issue just debating the sentence that round robin is not load balancing

Author

Commented:
OK....since we use an alias that points to the virtual node of the nlb cluster, is it acceptable to simply change the alias to point to one of the two physical nodes rather than the virtual one ? This way the change is very straight-through.
AkhaterSolutions Architect
Commented:
Yes off course this is the way to do it
AkhaterSolutions Architect

Commented:
Should have enough info to answer the request

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