Synthetic DNS timeouts

AntonioSousa — Thu, 21 Jul 2022 14:26:15 GMT

I have some synthetic measurements that were occasionally giving some DNS errors. These measurements were being made from a private synthetic location running on a Linux server.

I couldn't imagine why they were occurring, so decided to dig further. As it was a private location, I just dumped all the DNS traffic.

To my surprise, there was the DNS query packet, than there was a second one after a little bit more than 5 seconds, and than a correct reply.

So, I imagined something was wrong with Dynatrace, but I believe I quickly found the reason for this behaviour:

Dynatrace times out DNS resolution at 5 seconds.
Linux apparently retransmits DNS queries after 5 seconds...

So, what seams to be happening is that being the timeouts from Dynatrace and the OS (Operating System) equal, Dynatrace will always give a timeout before the OS retries. This wouldn't happen in Windows, as it apparently times out after 1 second.

There are two solutions for this:

You change the default Linux behaviour, changing the DNS timeout to something lower.
Dynatrace can give access to an "advanced mode" where DNS timeouts can be reconfigured.

Of course, I believe there might be additional impacts. I have also created a Product Idea, so that behaviour can be consistent when running namely HTTP monitors on different OS ActiveGates:
https://community.dynatrace.com/t5/Dynatrace-product-ideas/DNS-timeout-for-HTTP-Monitor-should-be-1-second/idi-p/191008

Re: Synthetic DNS timeouts

ChadTurner — Tue, 10 Jan 2023 21:40:11 GMT

Great Tip @AntonioSousa

topic Re: Synthetic DNS timeouts in Dynatrace tips

Synthetic DNS timeouts

Re: Synthetic DNS timeouts