dnsdist: Add feature to create Telemetry Spans from LuaAction

[pieterlexis]

Short description

This PR adds a withTraceSpan method to DNSQuestion and DNSResponse that takes the name of the Span and the function that will be instrumented.
It also adds a setSpanAttribute method that allows for adding attributes to the Span.

We can bikeshed on the naming and implementation.

I've added Otto as a reviewer, as he mentioned wanting to have similar functionality in the Recursor.

This PR also fixes a small over-sight when creating a minimal Protobuf message where we did not add the TraceID to the message.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[pieterlexis]

@rgacogne I was thinking that this could be made easier. I could add the setSpanAttribute method to DNSQuestion and remove the Closer from the closure. This would allow 2 things:

1. Users could set attributes on the Rule's Span
2. There is no need to capture anything

Rule code would look like this:

function (dq)
  dq:setSpanAttribute("attr-in-the-rulespan", "my-value")
  dq:withTraceSpan(
    "my-span",
    function ()
      -- Do work
      dq:setSpanAttribute("attr-in-my-subspan", "other-value")
    end
  )
  Return DNSAction.None
end

[rgacogne]

That looks nice indeed, where would the closer live and how does dq reference the correct span?

[omoerbeek]

I would love to see this a bit simpler indeed.

[pieterlexis]

That looks nice indeed, where would the closer live and how does dq reference the correct span?

The closer would live outside of Lua and DNSQuestion:setSpanAttribute would use Tracer::getLastSpanID to get the correct SpanID to pass to Tracer::setSpanAttribute.

[pieterlexis]

I've updated the PR with new, simpler method that no longer requires a closer.

[rgacogne]

I love the simplicity of this version, great work!

[coveralls]

Pull Request Test Coverage Report for Build 23153198208

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 10953 unchanged lines in 110 files lost coverage.
• Overall coverage decreased (-4.7%) to 66.223%

---

Files with Coverage Reduction	New Missed Lines	%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	84.78%
pdns/query-local-address.cc	1	93.62%
pdns/validate.cc	1	68.16%
pdns/burtle.hh	2	97.59%
pdns/channel.hh	2	47.48%
pdns/dns.cc	2	87.39%
pdns/dnsdistdist/dnsdist-lua-bindings-kvs.cc	2	0.0%
pdns/dnsdistdist/dnsdist-lua.hh	2	0.0%
pdns/dnsdistdist/dnsdist-opentelemetry.cc	2	94.85%
pdns/epollmplexer.cc	2	83.85%

Totals
Change from base Build 23152810648:	-4.7%
Covered Lines:	107737
Relevant Lines:	150102

---

💛 - Coveralls