fix(dotnet): cover dotnet container requirements

[wojciechtobis]

Problem

Agent can't read dotnet application's data and log:
level=debug name=parca-agent ts=2023-07-27T16:23:24.738406352Z caller=cpu.go:316 component=cpu_profiler msg="failed to prefetch process info" pid=605299 err="failed to open proc 605299: stat /proc/605299: no such file or directory"

Changes

According to this documentation the changes are:

• Add two required variables
• Add SYS_ADMIN capability

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[maxbrunet]

That does not look right to me, failed to open proc 605299: stat /proc/605299: no such file or directory indicate that the process does not exist anymore (has exited) when the agent tries to fetch its info.

PerfCollect requires the SYS_ADMIN capability (in order to run the perf tool), so be sure the container is started with that capability.

We do not want to run perf, but enable the perfmap only, so the symbols (function names) are available to the agent. There should not be anymore requirements than DOTNET_PerfMapEnabled=1. I have tested this example, it works fine, see #18.

That kind of races happens from time to time and you will see these logs. While we are trying to reduce them, they cannot be avoided entirely. If it happens a whole lot, it is possible there could be a bug in the agent and we would appreciate a bug report on the agent repository, but from what you have shared, I do not believe the issue is in the Dotnet app here.

[wojciechtobis]

@maxbrunet Thanks for your comment, I had a problem with this dotnet demo app during hackathon, and I found this documentation that helps in my case (that's why I thought that creating a PR with working solution is a good idea). Thank you for explanation how it works under the hood.
And you're right, there is already a PR to parca-agent that should fix the root cause.