DNS MP – Noisy resolution time alerts, and how to deal with them
This is a problem in the 6.0.6480.0 version of the DNS MP.
You will likely see a lot of DNS Resolution Time alerts popping into your console – then disappearing.
This is because these alerts are generated by a monitor, which is frequently changing state. These alerts get auto-resolved when the monitor flips back to healthy status, by design.
The root cause of the problem, if often that the server is busy when we run our script to check the local DNS resolution response… and the default threshold is set to 1 second.
Even in some of the best DNS environments, with good hardware… we will find DNS servers on Domain Controllers can get busy… and this is compounded by SCOM running multiple scripts at the same time – from the ADMP and DNS MP… sometimes we cannot return results in less than 1 second.
The best thing to do – is to chart out your current environment, using the provided performance views in the MP…. and adjust this moniotr for your servers:
What I can see – is that my Server 2003 DC/DNS server, with only 1 zone, but running on a PIII 933 mhz CPU, with 512mb of RAM…. is taking a baseline of 2-3 seconds. I will override this monitor for this SERVER, or for ALL 2003 DNS servers… to be 5 seconds.
Granted – our expectation is that our DNS servers can respond to a DNS query faster than 5 seconds – but this number is relative… due to how OpsMgr is collecting it. So the goal here, is to look at what is normal when the server is functioning well, establish that as our baseline, and set the threshold just above it.
Now – my Server 2008 DC/DNS server, which has 1GB of ram, and is a VM on very fast disk, and has a better CPU available, has a baseline of .2 seconds… so I will leave this monitor alone, since it is obviously not changing state so frequently.
When a real problem arises, load increases, or DNS is performaing poorly, we will be alerted – because we will breach our *baseline*.
