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What happens if a Domino ICM server is down?

Posted on 2012-03-13
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Last Modified: 2013-11-16
Problem. I`ve got 2 Lotus Domino servers in a cluster. Regardless how good ICM is developed, how in the world is a browser able to find out on its own, how to use another IP adress if one Domino server goes down? Yes a mail server is handled by MX records, but there is none MX like records for "a-records or cnames" in a DNS server that I am aware of. In linux we have a cache server in front. Cache servers can determine an alternate server back end.

As far I can see this may only work if we use an ICM serverice installed in front of a Domino cluster. Am I right about this folks?

Best regards Tor Bruheim
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Question by:tbruheim1967
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Expert Comment

by:doninja
ID: 37718437
The ICM server is doing the same job as the Linux cache server in determining which domino server is available or busy etc. Both ICM and Linux cache have same issue if the box is down so you need to ensure it is on the most reliable system possible.

To provide best high availability you need total network access so you can have machines fail-over to the public IP address or have them use some IP level load balancing.

If you don't have that level of network access then you could be able to modify the DNS record for the ICM server and have it on a very low TTL so that clients will contact the DNS server frequently.  
The ICM service can be placed on multiple clustered servers and the DNS points at the current ICM. a monitoring system would change the DNS entry if primary ICM is unavailable.
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Author Comment

by:tbruheim1967
ID: 37719234
Thank you very much. You verified very important topics for me. The thing that got me confused was the Lotus Domino manual. It seems that the Domino Administrator help suggest the possibility to use 2 ICP servers. I have attached 2 help sections from the Domino Help database regarding ICM to describe this topic:
Example of multiple ICMs inside the clusterExample of multiple ICMs outside the cluster
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Author Comment

by:tbruheim1967
ID: 37720013
I've requested that this question be closed as follows:

Accepted answer: 0 points for tbruheim1967's comment #37719234

for the following reason:

According to the manual the solution from experts-exchange is not complete, but only partial. The manual from Lotus Domino must be taken into consideration before we end this thread.
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LVL 10

Accepted Solution

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doninja earned 2000 total points
ID: 37721527
Given a chance I can explain the idea behind the help manual images.
The use of two two ICM's either in a cluster or externally are in case the ICM server should go down. It is commonly used with DNS Round Robin record entries for random load balancing and in the event of a failure of an ICM then a refresh of a browser would get the alternate DNS address eventually and contact an operational ICM.

This does work but is not as complete as having some DNS entry change in case an ICM server is down for an extended period to stop not found errors for clients.

Once an ICM has been contacted connected the user should not connect to ICM again if they stay on the URL of the server redirected to.

If my comments where helpful then please points would be appreciated
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Author Closing Comment

by:tbruheim1967
ID: 37722295
Thank you very much. This was very useful. This was the exact answer I was looking for. It has dawn on me that an Ip sprayer will be a better solution in my case. I cannot rely 100 percent on this solution because it has weaknesses. Your answer put me on the right track. Thank you very much. Your solution was 100 percent correct to my questions.
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