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AOS Load Balancing

I've been questioned several times recently about AOS load balancing in Dynamics AX, and there seems to be quite a bit of confusion about how to properly configure AX for AOS load balancing, as well as high availability. Here are a few clarifications that apply to Dynamics AX version 4.0, AX 2009 and AX 2012:


  • The AX client configuration determines which AOS instance that client will connect to.
  • If multiple AOS instances are listed, it will simply go down the list until it establishes contact.
  • If the contacted AOS instance is part of a load balanced cluster, that AOS will act as the load balancer. If not, the contacted AOS is used.
  • The load balancing logic is based on a count of current user sessions, and also takes into consideration the max concurrent sessions defined for the instance on the cluster.
  • If you have only one AOS instance listed in the client configuration, you have created a single point of failure. If no connection is established with that AOS, the client connection will fail, even if that AOS instance belongs to a cluster that has other AOS instances available for connection.

Recommended Configurations:

  • Every client configuration should point to all AOS instances in the cluster, thus eliminating the single point of failure.
  • Those AOS instances listed in the client configuration should belong to the load balanced cluster
  • A dedicated load balancer should only be used in high volume scenarios

Comments (3)
  1. Hi Jonathan,

    The most common implementation I've seen is to have a single copy of the application folder hosted on one of the AOS instances or a separate file server.

    The problem with having multiple application folders is maintenance and the risk of having them out of sync. I am not aware of any replication or sync mechanism, as you mention, but I'm sure if you do your due diligence you could pull it off. YOu would just have to ask yourself if it is worth the trouble/risk.

    Hosting the files on a clustered file server may have a limited benefit since the AOS service would not support automatic failover. You'd have to restart the AOS and client sessions would be lost. It might help you reduce downtime, though.

    In AX 2012, the application files are in the database, so it is a moot point.

  2. CustomerX says:

    I think might be good idear to make it clear about AX client now talks also directly to SSRS and WCF.

    AOS 2012 LB no longer covers reports, and customer must LB SSRS.

  3. Cody, I wonder if you could comment on the options, pros/cons and best strategy for locating the application files that the AOS must access. When you have multiple AOS instances it seems the most obvious options are :

    • hosting a single copy of the application files on one of the AOS instances;
    • having multiple copes on >1 AOS server with some sort or replication / sync mechanism;

    • putting the applciation files on a seperate high availability file share.

    Jonathan Howe

Comments are closed.

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