Iis – Windows NLB detect dead IIS

iisnlb

We're running 4 webservers through NLB, however every once in a while a single IIS dies on us (not the Windows, it still works, it's just the IIS returns 503 Service unavailable)

Is it somehow possible to setup NLB to detect this, and stop sending traffic to that particular server ?

Furthermore it'd be preferable if it could notify someone when this happens.

Best Answer

No, NLB cannot do this. But, you can write a script that verifies that IIS is working, and if it is not, send a msg to NLB to unload that node from the cluster.

Related Solutions

NLB configuration

NLB will distribute the load according to the chosen filtering mode & affinity settings for your NLB cluster. If you've set "Single" filtering mode, all traffic will go to a single server. If you've selected "Multiple host", the affinity decides which host will receive the traffic of recurring users. If you've chosen Single/Class C affinity, all users from the same IP / IP class C range will hit the same server (beware proxies & internal network topologies in this case).

Furthermore, even in multiple host mode, you can choose a distribution factor under the port rules so one server may be at 100% while the other is at 0%.

I've got a short video on my blog on how to setup a simple NLB cluster that shows the filtering mode & affinity settings: http://improve.dk/blog/2008/03/08/using-network-load-balancing-for-availability-and-scalability

IIS serving static content gives 503 at random

Maybe the problem are the RequestQueue/ConcurrentRequest limits. Consider the settings of the accepted answer on this Stack Overflow question:

IIS 7.0 503 errors with generic handler (.ashx) implementing IHttpAsyncHandler

To eliminate the 503 errors required 3 different config changes:

machine.config:
<configuration>
...  
   <system.web>  
    ...  
      <processModel enable="true" requestQueueLimit="100000"/>
IIS Manager > ApplicationPools > Advanced Settings
Queue Length : 65535
and finally (the missing piece of the puzzle), the command line:
appcmd.exe set config /section:serverRuntime /appConcurrent

Best Answer

Related Solutions

NLB configuration

IIS serving static content gives 503 at random

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