IIS 7 and Above
Application Request Routing (ARR)
ARR 3.0 removed some load Balancing algorithms
Last post Sep 27, 2017 07:46 AM by Jozef Woo
Aug 03, 2017 07:33 AM|Jozef Woo|LINK
As some of you might now, with ARR 3.0 some algorithms have been removed (compared to ARR 2.0).
I was interested in the "least current request" algorithm of ARR 2.0 which seems to be the "smartest" option, smarter than the current default round robin at least.
Does anyone have an idea why some of the algorithms have been removed? And which is the best alternative in combination with Exchange (2016) ? I would prefer something more intelligent than round robin. For round robin I could use DNS as well or is there
still a difference?
Many thanks for the help!
Aug 03, 2017 08:09 AM|Yuk Ding|LINK
Hi Jozef Woo,
The least current request has been removed with unsure reason. I assume the reason for this issue is if an IIS server broken, the arr will keep routing the request tot he broken server while ARR itself doesn't have the failover cluster function and the broken
server should have least concurrent request.
In addition, I think the weight round robin should be the smartest algorithm, you could customize the weight to change the load of different servers. I think both least current request and weight round robin could achieve the same load performance.
I think the DNS loadbalance is quite different from ARR load balance. Especially when you need to direct expose the backend server to client. ARR could be used as reverse proxy to prevent user from access the server directly.
Sep 13, 2017 08:22 AM|jccopp1|LINK
What about least response time? Can you please suggest an alternative solution? Some requests take longer to compute (data dependent) so it makes sense to route to another host that might be more responsive.
Removing a feature without explanation (except for saying "removed) or providing an alternative solution is kind of a miss with the new version of ARR.
Sep 14, 2017 03:59 AM|mahamr|LINK
Based on an internal thread from a while back, here's the reason from the Product Group:
"The algorithms were removed because they were confusing to customers, and we no longer wished to support those code paths. We recommend round robin
as a replacement."
Decisions like this aren't made lightly, and the Product Group knows best, so your best bet is to use round robin.
Sep 14, 2017 07:08 AM|Jozef Woo|LINK
Hi Mahamr, thank you for that information. I must say that for me personally, they removed the algorithms that were not confusing and left the ones that are confusing :-P
In any case, I picked round robin for my setup so that's the good one then.
Btw, would you happen to have any information about using ARR for ADFS? Because it was suggested as a solution by the Exchange team from Microsoft but I can't find any information about that. Do you have any internal information about that or are you able
to point me in a direction?
Sep 27, 2017 06:50 AM|Yuk Ding|LINK
All the official document should be public. This link provide the steps to use ARR with ADFS:
Sep 27, 2017 07:46 AM|Jozef Woo|LINK
Hi Yuk Ding, thanks but that (rather old) article doesn't seem to apply anymore. We are now having ADFS 2016 and ARR 3.0 and no documentation about that combination seems to exist. When trying it in multiple scenarios, we have found it not to work.