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Fix for systemd-resolved DNS incompatibility #82
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vannrt
requested review from
dlipovetsky,
ojmhetar,
puneetguptanitj and
sarun87
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dlipovetsky and
sarun87
vannrt
commented
Dec 7, 2018
| NodeadmKubeletSystemdDropinTemplate = `[Service] | ||
| Environment="KUBELET_DNS_ARGS=--cluster-dns={{ .ClusterDNS }} --cluster-domain={{ .ClusterDomain }}" | ||
| Environment="KUBELET_EXTRA_ARGS=--max-pods={{ .MaxPods }} --fail-swap-on={{ .FailSwapOn }} --hostname-override={{ .HostnameOverride }} --kube-api-qps={{ .KubeAPIQPS }} --kube-api-burst={{ .KubeAPIBurst }} --feature-gates={{ .FeatureGates}} --eviction-hard={{ .EvictionHard }} --cpu-manager-policy={{ .CPUManagerPolicy }} --kube-reserved={{ .KubeReservedCPU }}" | ||
| Environment="KUBELET_EXTRA_ARGS=--resolv-conf=/run/systemd/resolve/resolv.conf --max-pods={{ .MaxPods }} --fail-swap-on={{ .FailSwapOn }} --hostname-override={{ .HostnameOverride }} --kube-api-qps={{ .KubeAPIQPS }} --kube-api-burst={{ .KubeAPIBurst }} --feature-gates={{ .FeatureGates}} --eviction-hard={{ .EvictionHard }} --cpu-manager-policy={{ .CPUManagerPolicy }} --kube-reserved={{ .KubeReservedCPU }}" |
Contributor
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We should probably ask one of our customers how they were able to bypass this issue. Based on last night's demo, they seem to prep the machine's networking prior to running cctl.
This problem occurs because kube-dns on systems using systemd-resolved copy 127.0.0.53 from the host's /etc/resolv.conf. Since 127.0.0.53 is a loopback address, dns queries never get past kube-dns causing our conformance tests to fail on DNS related issues. More discussion here: kubernetes/kubernetes#45828 Related issues: kubernetes/kubeadm#787 kubernetes/kubeadm#273 kubernetes/kubeadm#845 The upstream fix is now in v1.11. Without the fix, the kubedns and dnsmasq containers would copy the host's `/etc/resolv.conf`: ``` \# This file is managed by man:systemd-resolved(8). Do not edit. \# \# This is a dynamic resolv.conf file for connecting local clients to the \# internal DNS stub resolver of systemd-resolved. This file lists all \# configured search domains. \# \# Run "systemd-resolve --status" to see details about the uplink DNS servers \# currently in use. \# \# Third party programs must not access this file directly, but only through the \# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way, \# replace this symlink by a static file or a different symlink. \# \# See man:systemd-resolved.service(8) for details about the supported modes of \# operation for /etc/resolv.conf. nameserver 127.0.0.53 search platform9.sys ``` After the fix: ``` \# This file is managed by man:systemd-resolved(8). Do not edit. \# \# This is a dynamic resolv.conf file for connecting local clients directly to \# all known uplink DNS servers. This file lists all configured search domains. \# \# Third party programs must not access this file directly, but only through the \# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way, \# replace this symlink by a static file or a different symlink. \# \# See man:systemd-resolved.service(8) for details about the supported modes of \# operation for /etc/resolv.conf. nameserver 10.105.16.2 nameserver 10.105.16.4 search platform9.sys ```
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Dec 11, 2018
| NodeadmKubeletSystemdDropinTemplate = `[Service] | ||
| Environment="KUBELET_DNS_ARGS=--cluster-dns={{ .ClusterDNS }} --cluster-domain={{ .ClusterDomain }}" | ||
| Environment="KUBELET_EXTRA_ARGS=--max-pods={{ .MaxPods }} --fail-swap-on={{ .FailSwapOn }} --hostname-override={{ .HostnameOverride }} --kube-api-qps={{ .KubeAPIQPS }} --kube-api-burst={{ .KubeAPIBurst }} --feature-gates={{ .FeatureGates}} --eviction-hard={{ .EvictionHard }} --cpu-manager-policy={{ .CPUManagerPolicy }} --kube-reserved={{ .KubeReservedCPU }}" | ||
| Environment="KUBELET_EXTRA_ARGS=--resolv-conf=/run/systemd/resolve/resolv.conf --max-pods={{ .MaxPods }} --fail-swap-on={{ .FailSwapOn }} --hostname-override={{ .HostnameOverride }} --kube-api-qps={{ .KubeAPIQPS }} --kube-api-burst={{ .KubeAPIBurst }} --feature-gates={{ .FeatureGates}} --eviction-hard={{ .EvictionHard }} --cpu-manager-policy={{ .CPUManagerPolicy }} --kube-reserved={{ .KubeReservedCPU }}" |
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Even though this is a temp workaround before 1.11, I think /run/systemd/solve/resolv.conf should be placed into a constant and substituted via this template like the other flags.
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@vannrt As I understand it, |
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This problem occurs because kube-dns on systems using systemd-resolved
copy 127.0.0.53 from the host's /etc/resolv.conf.
Since 127.0.0.53 is a loopback address, dns queries never get past
kube-dns causing our conformance tests to fail on DNS related issues.
More discussion here: kubernetes/kubernetes#45828
Related issues:
kubernetes/kubeadm#787
kubernetes/kubeadm#273
kubernetes/kubeadm#845
The upstream fix is now in v1.11.
Without the fix, the kubedns and dnsmasq containers would copy the host's
/etc/resolv.conf:After the fix: