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This product reached the end of support date on March 31, 2021.

App Mon can't perform CPU sampling, firewall issue?


Hi, I'm having issues in this fairly large distributed setup in which within the same production datacenter, there are web, app and ESB tiers located in separate subnets. All 3 subnets are routed via a L3 firewall. The Collector is located in its own subnet for data center policy reasons.

Agent to collector communications are working fine, with low class transformation time during startup and discovery runs. Everything is normal with the exception of CPU sampling. Whenever a CPU sample is done, it either does not complete or it completes successfully but without any content. Is this an indication that potentially the firewall may be interfering? I'm asking because it is a recommendation in the App Mon documentation to not route Agent to Collector traffic through a firewall.

However to have multiple Collectors in this environment is not really feasible plus such a setup works for another application within the same data center. I'm wondering if this can be due to that specific firewall or some environmental issue with the application. Currently the firewall team is disputing this because there are no error or blocking/dropped packets in that firewall's logs.

Would love to hear some 2 cents if anyone else encountered this before.


Dynatrace Leader
Dynatrace Leader

Have you looked in the server/agent logs around when you try to run a sample to see if anything stands out?

I agree with James. Look at the Collector, Server and also Agent logs to see if there is any indication of an error. While we do not recommend a Firewall between agent and collector it seems that your agents connected successfully and collect PurePath data. The CPU Sample uses the same communication channels and should therefore work just as fine. There might be something else going on here, e.g: a JVM version that doesnt support CPU Sampling, ...