I think I just found the smoking gun, so to speak. In the reproducible builds log, I spotted this:
=== RUN TestDNSProtocol
dns_test.go:490: "localhost" doesn't resolve to ::1.
--- SKIP: TestDNSProtocol (0.00s)
This is due to this check in TestDNSProtocol:
_, err := net.ResolveIPAddr("ip6", "localhost")
if err != nil {
t.Skip("\"localhost\" doesn't resolve to ::1.")
}
The failure of "localhost" resolving to ::1 (as well as 127.0.0.1)
suggests that the reproducible builds environment does not conform to a
typical Debian environment (where localhost resolves to both 127.0.0.1
_and_ ::1), and will cause the GRPC tests to fail, since the upstream
developer sets "IPProtocolFallback: false", and blackbox_exporter's
resolver defaults to ip6[1].
I will prepare a patch to set "IPProtocolFallback: true" in the GRPC tests, as it is in all other tests in the repo (and as per the documented runtime config defaults).
[1]: https://github.com/prometheus/blackbox_exporter/issues/969#issuecomment-1370452161
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