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Does Http through proxy do a DNS lookup every time?

esamurai

We are using the Http monitor, and have three monitors set up to go through proxy. Our proxies are DNS round-robin load-balanced. My question is: since I use a name for the proxy in the Http-through-proxy APM monitor, is that name being resolved every time the monitor runs, or is it using the IP address that was found/resolved for the proxy when I built the monitor?

Our monitors are showing a lot of what seem to be false events, where the http component goes critical. The time-outs are set for 4000=warning and 8000=critical.

I am thinking of setting up test monitors which will point directly to a specific proxy, and seeing which ones go critical.

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    My question is: since I use a name for the proxy in the Http-through-proxy APM monitor, is that name being resolved every time the monitor runs, or is it using the IP address that was found/resolved for the proxy when I built the monitor?

    This will depend on the DNS caching of the server your running APM. If the entry still exists in the operating system's DNS cache of the APM server then there is no need to re-resolve the name to an IP address. You can view the client cache of the server by running "ipconfig /displaydns". This will also show you the TTL which is the expected time for this entry to expire. 

    Rebooting the server will also cause the DNS cache to be flushed forcing the client to re-resolve any names to IP addresses again. To prevent DNS lookups from occurring you could always enter the IP address instead of the FQDN. Alternatively you could place entries in your hosts file to resolve these names locally on the host. This file is located in C:\Windows\System32\drivers\etc

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    My question is: since I use a name for the proxy in the Http-through-proxy APM monitor, is that name being resolved every time the monitor runs, or is it using the IP address that was found/resolved for the proxy when I built the monitor?

    This will depend on the DNS caching of the server your running APM. If the entry still exists in the operating system's DNS cache of the APM server then there is no need to re-resolve the name to an IP address. You can view the client cache of the server by running "ipconfig /displaydns". This will also show you the TTL which is the expected time for this entry to expire. 

    Rebooting the server will also cause the DNS cache to be flushed forcing the client to re-resolve any names to IP addresses again. To prevent DNS lookups from occurring you could always enter the IP address instead of the FQDN. Alternatively you could place entries in your hosts file to resolve these names locally on the host. This file is located in C:\Windows\System32\drivers\etc

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