[dockerd] Force usage of cgo DNS resolver (#13649)
Go's runtime (and dockerd inherits this) uses own DNS resolver implementation by default on Linux. It has been observed that there are some DNS resolution issues when executing ```docker pull``` after first boot. Consider the following script: ``` admin@r-boxer-sw01:~$ while :; do date; cat /etc/resolv.conf; ping -c 1 harbor.mellanox.com; docker pull harbor.mellanox.com/sonic/cpu-report:1.0.0 ; sleep 1; done Fri 03 Feb 2023 10:06:22 AM UTC nameserver 10.211.0.124 nameserver 10.211.0.121 nameserver 10.7.77.135 search mtr.labs.mlnx labs.mlnx mlnx lab.mtl.com mtl.com PING harbor.mellanox.com (10.7.1.117) 56(84) bytes of data. 64 bytes from harbor.mtl.labs.mlnx (10.7.1.117): icmp_seq=1 ttl=53 time=5.99 ms --- harbor.mellanox.com ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 5.989/5.989/5.989/0.000 ms Error response from daemon: Get "https://harbor.mellanox.com/v2/": dial tcp: lookup harbor.mellanox.com on [::1]:53: read udp [::1]:57245->[::1]:53: read: connection refused Fri 03 Feb 2023 10:06:23 AM UTC nameserver 10.211.0.124 nameserver 10.211.0.121 nameserver 10.7.77.135 search mtr.labs.mlnx labs.mlnx mlnx lab.mtl.com mtl.com PING harbor.mellanox.com (10.7.1.117) 56(84) bytes of data. 64 bytes from harbor.mtl.labs.mlnx (10.7.1.117): icmp_seq=1 ttl=53 time=5.56 ms --- harbor.mellanox.com ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 5.561/5.561/5.561/0.000 ms Error response from daemon: Get "https://harbor.mellanox.com/v2/": dial tcp: lookup harbor.mellanox.com on [::1]:53: read udp [::1]:53299->[::1]:53: read: connection refused Fri 03 Feb 2023 10:06:24 AM UTC nameserver 10.211.0.124 nameserver 10.211.0.121 nameserver 10.7.77.135 search mtr.labs.mlnx labs.mlnx mlnx lab.mtl.com mtl.com PING harbor.mellanox.com (10.7.1.117) 56(84) bytes of data. 64 bytes from harbor.mtl.labs.mlnx (10.7.1.117): icmp_seq=1 ttl=53 time=5.78 ms --- harbor.mellanox.com ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 5.783/5.783/5.783/0.000 ms Error response from daemon: Get "https://harbor.mellanox.com/v2/": dial tcp: lookup harbor.mellanox.com on [::1]:53: read udp [::1]:55765->[::1]:53: read: connection refused Fri 03 Feb 2023 10:06:25 AM UTC nameserver 10.211.0.124 nameserver 10.211.0.121 nameserver 10.7.77.135 search mtr.labs.mlnx labs.mlnx mlnx lab.mtl.com mtl.com PING harbor.mellanox.com (10.7.1.117) 56(84) bytes of data. 64 bytes from harbor.mtl.labs.mlnx (10.7.1.117): icmp_seq=1 ttl=53 time=7.17 ms --- harbor.mellanox.com ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 7.171/7.171/7.171/0.000 ms Error response from daemon: Get "https://harbor.mellanox.com/v2/": dial tcp: lookup harbor.mellanox.com on [::1]:53: read udp [::1]:44877->[::1]:53: read: connection refused Fri 03 Feb 2023 10:06:26 AM UTC nameserver 10.211.0.124 nameserver 10.211.0.121 nameserver 10.7.77.135 search mtr.labs.mlnx labs.mlnx mlnx lab.mtl.com mtl.com PING harbor.mellanox.com (10.7.1.117) 56(84) bytes of data. 64 bytes from harbor.mtl.labs.mlnx (10.7.1.117): icmp_seq=1 ttl=53 time=5.66 ms --- harbor.mellanox.com ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 5.656/5.656/5.656/0.000 ms Error response from daemon: Get "https://harbor.mellanox.com/v2/": dial tcp: lookup harbor.mellanox.com on [::1]:53: read udp [::1]:54604->[::1]:53: read: connection refused Fri 03 Feb 2023 10:06:27 AM UTC nameserver 10.211.0.124 nameserver 10.211.0.121 nameserver 10.7.77.135 search mtr.labs.mlnx labs.mlnx mlnx lab.mtl.com mtl.com PING harbor.mellanox.com (10.7.1.117) 56(84) bytes of data. 64 bytes from harbor.mtl.labs.mlnx (10.7.1.117): icmp_seq=1 ttl=53 time=8.22 ms --- harbor.mellanox.com ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 8.223/8.223/8.223/0.000 ms 1.0.0: Pulling from sonic/cpu-report 004f1eed87df: Downloading [===================> ] 19.3MB/50.43MB 5d6f1e8117db: Download complete 48c2faf66abe: Download complete 234b70d0479d: Downloading [=========> ] 9.363MB/51.84MB 6fa07a00e2f0: Downloading [==> ] 9.51MB/192.4MB 04a31b4508b8: Waiting e11ae5168189: Waiting 8861a99744cb: Waiting d59580d95305: Waiting 12b1523494c1: Waiting d1a4b09e9dbc: Waiting 99f41c3f014f: Waiting ``` While /etc/resolv.conf has the correct content and ping (and any other utility that uses libc's DNS resolution implementation) works correctly docker is unable to resolve the hostname and falls back to default [::1]:53. This started to happen after PR https://github.com/sonic-net/sonic-buildimage/pull/13516 has been merged. As you can see from the log, dockerd is able to pick up the correct /etc/resolv.conf only after 5 sec since first try. This seems to be somehow related to the logic in Go's DNS resolver https://github.com/golang/go/blob/master/src/net/dnsclient_unix.go#L385. There have been issues like that reported in docker like: - https://github.com/docker/cli/issues/2299 - https://github.com/docker/cli/issues/2618 - https://github.com/moby/moby/issues/22398 Since this starts to happen after inclusion of resolvconf package by above mentioned PR and the fact I can't see any problem with that (ping, nslookup, etc. works) the choice is made to force dockerd to use cgo (libc) resolver. Signed-off-by: Stepan Blyschak <stepanb@nvidia.com>
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Stepan Blyshchak
mssonicbld
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[Service]
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Environment=GODEBUG=netdns=cgo
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ExecStart=
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ExecStart=/usr/bin/dockerd -H unix:// --storage-driver=overlay2 --bip=240.127.1.1/24 --iptables=false --ipv6=true --fixed-cidr-v6=fd00::/80
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