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Add High Avaliablity for the Exchange 2010 Web Services ( AutoDiscover, EWS,Active-Sync)

Posted on 2013-10-22
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Last Modified: 2013-11-06
Hello,

We have Exchange 2010 Sp2 with 3 Exchange 2010 Multi-Role Servers. All three servers are part of the DAG.  
Currently they use DNS Load balancing for the CAS availability . Server names are SRv1, SRV2, SRV3.

DNS host name for Load balancing is Mail.contoso.com ( with 3 Ip address of exchange servers )

They pointed all the Internal and External URLs in to the SRV2. If SRV 2 goes down, all the web services will be unavailable.

Can we point all the URLs to the CAS DNS Load Balancing Host name ? (mail.contoso.com)
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Question by:Kanchana_Silva
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Expert Comment

by:PraveenBalan
ID: 39593211
Preferred Option:
Ideally you will need a Loadbalancer when you have multi-role exchange server,  and added all into DAG (only if you have interested to invest more on messaging infra).

Second option:
I would need the outlook auto discovery information of one of the users to check the web URL details.

- alternately,

you can keep external URL as your registered external OWA url for all web services, so that you will need to modify only the firewall NAT to take care of internet client access.

Internal URLs for all these are having SRV records, and the failover would automatically happen.

without a load balancing, you will not be achieve fully automated redundancy in client access, some level of manual intervention is necessary to manage the operations in case of primary web service server goes down.

-Praveen
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Author Comment

by:Kanchana_Silva
ID: 39593375
let me know how  OWA / Active-Sync / EWS having SRv records ?

I know auto discover has SRV, but how will it do the automatic Failover ?

regards
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Expert Comment

by:PraveenBalan
ID: 39593389
autodiscover will find the available internal URLs for the necessary internal URLs for outlook, for e.g. the OOF, OAB  etc.

With respect to ActiveSync, do you use internal URL ? it will be the internet registered URL I hope, which is set as External URL properties of ActiveSync website. The shifting of ActSync will happen when you do the changes at firewall NATing.

How do you access the OWA, do you have 2 seperate URLs (internet and intranet) ? If you have single registered URL, it can be taken care on public NATing, and DNS entries. Or if you use one of the server FQDNs, you will have issues (you may use the same URLs internally and externally for OWA to avoid confusions).
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Author Comment

by:Kanchana_Silva
ID: 39593439
You did not take my point.

I am not asking how AutoDiscover works. Autodiscover is taking the urls what we configured in the Virtual Directores.

I am asking give failover part for those Urls.
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Expert Comment

by:PraveenBalan
ID: 39593604
I hope you have configured the internal URL of web services as below,

" serverfqdn/ews "

think that one of the exchange server which gives the web services is down, and you are trying to open the outlook. The outlook will try to reach this server and on failure it will look for another available server through active directory.

the details are little in dept, as it in turns query different sources in active directory like srv, scp (service connection point), .. and so on.

look at the white paper from MS,
http://technet.microsoft.com/en-us/library/jj591328(v=exchg.141).aspx#BKMK_OutlookAndAutodiscover

section - "How the Autodiscover service works with clients".

the article exhibits,

When a new Outlook profile is configured or updated
When a client periodically checks for changes to the Web Services URLs
When underlying network connection changes occur in your messaging environment

hope this will give you an idea how it changes.
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Author Comment

by:Kanchana_Silva
ID: 39593668
Nope, this talking about modifying the Web service Urls then effect that on Outlook client so on
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Accepted Solution

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PraveenBalan earned 250 total points
ID: 39593703
I was trying to explain you about the possibility of managing the infra without a use a LB cluster/appliance. From your response, I assume/understand that you need a complete fail over solution including the client access.

As I pen down previously, the load balancer is required for a fully functional failover. without which you will not be able to accomplish the Client Access Failover.

Since you added the server into DAG(failover cluster), you will not be able to create a Windows LB cluster. You will need to go for a LB solution like kemp, f5, Cisco etc.

look at http://technet.microsoft.com/en-us/library/ff625247.aspx#recommendations


With regards to your question "Can we point all the URLs to the CAS DNS Load Balancing Host name"
Personally I do not recommend because few request will still go to unavailable server, as the DNS will not verify for the availability of services when responding to the client requests.
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Assisted Solution

by:Simon Butler (Sembee)
Simon Butler (Sembee) earned 250 total points
ID: 39596795
If you configure a split dns system, your external host name will resolve internally. You will need to adjust Exchange to use the external host name internally.

http://semb.ee/hostnames

How are you doing this:

"Currently they use DNS Load balancing for the CAS availability "

DNS has no load balancing capability, so either you are doing round robin or you have a load balancer.

Simon.
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