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HA functionality when DNS is lost?

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HA functionality when DNS is lost? - 14.Sep.2010 8:09:42 AM   
JustinC71

 

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HA relies heavily on DNS, but how long will it continue to function when DNS goes offline? I assume it will function until the host needs to refresh it's DNS cache, at which point it will be unable to resolve it's peers and HA functionality will be broken...but I don't have a lab set up to properly test that at the moment. Anyone have any insight into this particular issue?

I know Scott has blogged about HA in regard to isolation response and DNS importance, but I can't find anything related to DNS failure...
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RE: HA functionality when DNS is lost? - 14.Sep.2010 10:19:53 AM   
`ariel

 

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 Good point, a few days ago i was setting up a lab at work and HA cant be enable without proper DNS functionality... i will try deleting the record A that i create for the lab and post back with result.

Justin you want the time that HA keep working without DNS ?

< Message edited by `ariel -- 14.Sep.2010 10:21:36 AM >


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RE: HA functionality when DNS is lost? - 15.Sep.2010 8:57:51 AM   
JustinC71

 

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quote:

ORIGINAL: `ariel

Good point, a few days ago i was setting up a lab at work and HA cant be enable without proper DNS functionality... i will try deleting the record A that i create for the lab and post back with result.

Justin you want the time that HA keep working without DNS ?


Hey ariel, thanks for your reply!  Yes, I'm trying to determine exactly what will happen to HA when DNS goes offline...as in will it break right away, after an hour, or just keep working without any errors. 

Someone on the VMware Communities board has said that HA actually inserts it's peer addresses into the /etc/hosts file and doesn't need DNS after configuration...?  If so, that's news to me.  I've configured HA before and viewed the /etc/hosts file afterwards (well, with esx 3.5 at least) and it didn't add anything.  I have a client that wants to install DNS on the vCenter server and expects HA to function properly even if the vCenter server (and now DNS) goes offline.  Just trying to model that scenario but don't really have a lab to work with right now.

http://communities.vmware.com/thread/284475?tstart=0

EDIT: After looking through the /etc/hosts files on some of my HA nodes, it looks as if the IP for one primary HA node is added to the file.  That would indeed keep the cluster functional, but if a primary were to fail while DNS is offline the cluster would lose connectivity to more than one node.

< Message edited by JustinC71 -- 15.Sep.2010 9:13:52 AM >

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RE: HA functionality when DNS is lost? - 16.Sep.2010 10:30:45 AM   
`ariel

 

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 The entry for the 2 nodes of my test cluster was deleted and the HA keep working, i can't test if one node goes down because is only a 2 node cluster so the second node got the VMs and wait the primary node..

node1 /etc/hosts
/etc # cat hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1       localhost.localdomain localhost
::1             localhost.localdomain localhost
172.17.47.159   x1.lab.local x1
/etc #

node2 /etc/hosts
/etc # cat hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1       localhost.localdomain localhost
::1             localhost.localdomain localhost
172.17.47.161   x2.lab.local x2
172.17.47.159 x1 # Added by VMware HA
/etc #

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RE: HA functionality when DNS is lost? - 22.Sep.2010 9:08:01 AM   
JustinC71

 

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Thanks for checking it out, looks like we're pretty certain that DNS is not a huge factor once HA is configured these days.  I asked Duncan over at yellow-bricks.com about this, here's what he had to say: 

"no as of 4.1 the dependency on DNS has been completely removed. besides /etc/hosts there is also ft_hosts which holds name resolution info. When DNS is unavailable it will use the hosts file or the ft_hosts file. At least theoretically, I haven't tested this to be honest;"


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RE: HA functionality when DNS is lost? - 22.Sep.2010 10:49:00 AM   
`ariel

 

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 Great! Good info.
looks like DNS is a prerequisite just for the initial setup. 

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RE: HA functionality when DNS is lost? - 13.Oct.2011 9:02:49 PM   
shenglu

 

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I set up the laboratory work and the Hospital Authority can not make incorrect DNS feature ... I will try to delete the record I created a laboratory and results returned.

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