net/http: TestTransportEventTraceRealDNS fails consistently

[odeke-em]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version devel +5552d08 Sat Oct 29 18:36:48 2016 +0000 darwin/amd64
tip at 5552d08

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN="/Users/emmanuelodeke/go/bin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/emmanuelodeke/go"
GORACE=""
GOROOT="/Users/emmanuelodeke/go/src/go.googlesource.com/go"
GOTOOLDIR="/Users/emmanuelodeke/go/src/go.googlesource.com/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/v3/7z434qpx5v3bw0wh8h2myfpw0000gn/T/go-build205502808=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

$ cd net/http
$ for i in $(seq 1 10);do echo "Trial $i at $(date)" >> log;go test -run=TestTransportEventTraceRealDNS 2>&1 >> log;echo -e "\n" >> log;done

What did you expect to see?

All pass or a flake in the worst case.

What did you see instead?

Trial 1 at Sat 29 Oct 2016 18:41:15 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.53s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.545s


Trial 2 at Sat 29 Oct 2016 18:41:19 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.08s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.090s


Trial 3 at Sat 29 Oct 2016 18:41:22 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.07s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.082s


Trial 4 at Sat 29 Oct 2016 18:41:26 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.51s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.523s


Trial 5 at Sat 29 Oct 2016 18:41:31 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.07s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.081s


Trial 6 at Sat 29 Oct 2016 18:41:36 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.10s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.108s


Trial 7 at Sat 29 Oct 2016 18:41:40 PDT
--- FAIL: TestTransportEventTraceRealDNS (2.26s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    2.271s


Trial 8 at Sat 29 Oct 2016 18:41:46 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.08s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.090s


Trial 9 at Sat 29 Oct 2016 18:41:49 PDT
--- FAIL: TestTransportEventTraceRealDNS (0.09s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    0.105s


Trial 10 at Sat 29 Oct 2016 18:41:53 PDT
--- FAIL: TestTransportEventTraceRealDNS (1.44s)
    transport_test.go:3385: expected error during DNS lookup
FAIL
FAIL    net/http    1.449s

Is there something I change? I also tried running the test with CGO_ENABLED=0 go test -run=TestTransportEventTraceRealDNS but same results.

[odeke-em]

/cc @bradfitz

[odeke-em]

Perhaps this is a subset of #17472?

[bradfitz]

This test is testing "real DNS" and you don't have real DNS.

Change your DNS to 8.8.8.8 or another standards-conformant DNS provider and it'll pass.

Or run with -short (as run with all.bash) and it'll skip that.

[odeke-em]

Ahh, gotcha! Thanks

[hartzell]

I just tripped over a funny version of the problem.

I have a Digital Ocean droplet running an image based on their CentOS 7 image.

That machine was named foobar.dev.

/etc/resolv.conf contains only:

nameserver 8.8.8.8
nameserver 8.8.4.4

and /etc/nsswitch.conf contains (amongst others):

hosts:      files dns myhostname

For some reason, when it was unable to resolve dns-should-not-resolve.golang it tried dns-should-not-resolve.golang.dev (dig and host didn't have this problem, but ping does; I didn't track down why it was being so "helpful").

Things in .dev now resolve to 127.0.53.53, leading to the test failing.

My "fix" was to just rename the machine.