net: TestLookupDotsWithRemoteSource is flaky #27992

katiehockman · 2018-10-03T20:37:11Z

We are getting flaky test failures in net. This has been somewhat rare in the past few months, but it has failed the last 5 builds, so probably worth looking into now.

--- FAIL: TestLookupDotsWithRemoteSource (15.57s)
    lookup_test.go:694: LookupSRV(xmpp-server, tcp, google.com): lookup _xmpp-server._tcp.google.com on 8.8.8.8:53: read udp 10.50.0.170:50511->8.8.8.8:53: i/o timeout (mode=go)
FAIL
FAIL	net	30.123s

Looks very related to #16865 closed 2 years ago.

katiehockman · 2018-10-03T20:39:09Z

/cc @mikioh @brad-burch @ianlancetaylor

ianlancetaylor · 2018-10-03T20:52:43Z

ianlancetaylor · 2018-10-03T20:57:36Z

Any chance there was a recent change to whether the builders set GO_BUILDER_FLAKY_NET in the environment? Because the test does not fail in that way if that environment variable is set.

mikioh · 2018-10-03T23:52:32Z

Once http://golang.org/cl/102875 lands, I will smash the use of external DNS speakers such as rsc.io or some public full resolver then flaky tests disappear. For now, I have no spare time to debug the circumstances running the tests, also not sure there's a way to sneak in the (protected) circumstances.

andybons · 2018-11-28T20:16:04Z

@mikioh should we just disable this test until 1.13?

mikioh · 2018-11-29T00:02:48Z

Yes, please. Will try to allocate my spare time for Go 1.13 devel cycle.

gopherbot · 2018-11-29T23:45:08Z

Change https://golang.org/cl/151799 mentions this issue: net: skip flaky TestLookupDotsWithRemoteSource for now


        net: skip flaky TestLookupDotsWithRemoteSource on darwin

Updates #27992 Change-Id: Ic327df7cc5002a3d537f9117559c25f30e1eab9c Reviewed-on: https://go-review.googlesource.com/c/151799 Run-TryBot: Andrew Bonventre <andybons@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

andybons · 2018-11-30T22:25:34Z

@mikioh done. Assigning back to you. Thanks.

bcmills · 2019-05-15T13:44:01Z

Here's the same failure mode on dragonfly-amd64: https://build.golang.org/log/2f33b64e758b0fb89431e34f51f80580e5b56e59

--- FAIL: TestLookupDotsWithRemoteSource (10.85s)
    lookup_test.go:669: LookupCNAME(www.mit.edu, mode=go): lookup www.mit.edu on 192.168.1.100:53: read udp 192.168.1.2:54367->192.168.1.100:53: i/o timeout
FAIL
FAIL	net	68.224s

bcmills · 2019-08-20T18:12:53Z

freebsd-arm-paulzhol (https://build.golang.org/log/daa40802f66a0d79d4d356d551c94456f56785b1):

--- FAIL: TestLookupDotsWithRemoteSource (12.52s)
    lookup_test.go:656: LookupAddr(8.8.8.8): lookup 8.8.8.8.in-addr.arpa. on 192.168.1.253:53: read udp 192.168.1.101:38233->192.168.1.253:53: i/o timeout (mode=go)
FAIL
FAIL	net	44.919s

bcmills · 2020-01-27T14:00:34Z

2020-01-25T05:48:12-01df660/freebsd-arm-paulzhol
2019-11-22T16:04:32-1c5bd34/freebsd-arm-paulzhol
2019-10-26T05:40:14-c3e8a20/linux-s390x-ibm
2019-09-18T19:24:59-90f9426/freebsd-arm-paulzhol
2019-08-19T21:42:54-d6ffc1d/freebsd-arm-paulzhol
2019-07-29T16:52:01-5235501/freebsd-arm-paulzhol
2019-07-01T14:45:49-bc593ea/freebsd-arm-paulzhol
2019-06-19T18:19:01-b373d31/freebsd-arm-paulzhol
2019-05-14T16:36:38-a9e107c/dragonfly-amd64
2019-05-09T18:02:19-c514071/dragonfly-amd64
2019-05-02T04:44:36-74b3c50/dragonfly-amd64
2019-04-28T23:51:04-50ad094/dragonfly-amd64

bcmills · 2020-01-27T14:18:54Z

I did some digging, and I believe that this flakiness is caused by the hard-coded timeout and attempt limits in net/dnsconfig_unix.go:

go/src/net/dnsconfig_unix.go

Lines 41 to 45 in 825ff1e

    
           conf := &dnsConfig{ 
        
           	ndots:    1, 
        
           	timeout:  5 * time.Second, 
        
           	attempts: 2, 
        
           }

On my Linux workstation, man 5 resolv.conf reports these same defaults. However, given that the Go net.Resolver API accepts a context.Context which can provide its own timeout behavior, I think these hard-coded limits are out of place: they might make sense in the context of a legacy POSIX C API, but they don't really fit in a modern Go package.

I would recommend:

Complete this TODO to allow the Resolver to override the system-default timeout (and likely also the default limit on attempts).
Refactor the RemoteSource test to use a Resolver and explicit Context instead of the Context-less top-level LookupAddr function. Bound the timeout and number of retries to the test's deadline (#28135) instead of arbitrary constants.

katiehockman added OS-Darwin Testing labels Oct 3, 2018

ianlancetaylor added the release-blocker label Oct 3, 2018

ianlancetaylor added this to the Go1.12 milestone Oct 3, 2018

katiehockman changed the title ~~net: Flaky test failing in darwin-amd64-10_10~~ net: flaky test failing in darwin-amd64-10_10 Oct 3, 2018

bradfitz mentioned this issue Oct 4, 2018

net: localhost pipes cause test hangs on macOS Sierra #25696

Closed

andybons self-assigned this Nov 29, 2018

andybons assigned mikioh and unassigned andybons Nov 30, 2018

andybons removed the release-blocker label Nov 30, 2018

andybons modified the milestones: Go1.12, Go1.13 Nov 30, 2018

mikioh removed their assignment Dec 4, 2018

bcmills changed the title ~~net: flaky test failing in darwin-amd64-10_10~~ net: TestLookupDotsWithRemoteSource is flaky May 15, 2019

bcmills added the NeedsFix label May 15, 2019

andybons modified the milestones: Go1.13, Go1.14 Jul 8, 2019

bcmills removed the OS-Darwin label Aug 20, 2019

rsc removed this from the Go1.14 milestone Oct 9, 2019

rsc added this to the Backlog milestone Oct 9, 2019

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net: TestLookupDotsWithRemoteSource is flaky #27992

net: TestLookupDotsWithRemoteSource is flaky #27992

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net: TestLookupDotsWithRemoteSource is flaky #27992

net: TestLookupDotsWithRemoteSource is flaky #27992

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