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[release-4.8] Bug 2016275: [on-prem] Set coredns bufsize to 512 #2807

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merged 1 commit into from Oct 26, 2021
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[release-4.8] Bug 2016275: [on-prem] Set coredns bufsize to 512 #2807

merged 1 commit into from Oct 26, 2021

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This is an automated cherry-pick of #2784

/assign mandre

@miheer
Bug 1991067: [on-prem] Set coredns bufsize to 512
dd420c0 
KNI CoreDNS does not resolve hostnames if the nameservers in the forwarders provide a DNS reponse > 512 bytes

So name resolution to github.com from application pod fails if the forward section of Corefile had an upstream DNS which provides a DNS response > 512

The response size you get while dig to github.com using upstream namserver 10.11.142.1  is 602 whereas using namserver 10.11.5.19 it is 55

The limit for UDP DNS messages is 512 bytes long. Well behaved DNS servers are supposed to truncate the message and set the truncated bit. See RFC 1035 section 4.2.1.

https://datatracker.ietf.org/doc/html/rfc1035#section-4.2.1

https://datatracker.ietf.org/doc/html/rfc1035#section-2.3.4

The difference in the dig to github.com is the response size. For  10.11.142.1 it is 602 > 512 and for 10.11.5.19 it is 55 < 512

CoreDNS will compress messages that exceed 512 bytes, unless the client allows a larger maximum size by sending the corresponding edns0 option in the request.

dig in particular sends a buffer size > 512 by default. I think the exact number depends on the dig version or perhaps the environment... on my OCP nodes it defaults to 4096 - I think this is most common.

[miheer@localhost ~]$ oc debug node/mykrbid-vcd8j-worker-0-hlkmf
Starting pod/mykrbid-vcd8j-worker-0-hlkmf-debug ...
To use host binaries, run `chroot /host`
Pod IP: 192.168.0.94
If you don't see a command prompt, try pressing enter.
sh-4.4#
sh-4.4# sysctl -a | grep  rmem
net.core.rmem_default = 212992
net.core.rmem_max = 212992
net.ipv4.tcp_rmem = 4096	87380	6291456
net.ipv4.udp_rmem_min = 4096

So, we should be setting 512 as bufsize for KNI coredns to avoid this issue.
@openshift-cherrypick-robot openshift-cherrypick-robot mentioned this pull request Oct 21, 2021
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openshift-ci bot commented Oct 21, 2021

@openshift-cherrypick-robot: Bugzilla bug 2009210 has been cloned as Bugzilla bug 2016275. Retitling PR to link against new bug.
/retitle [release-4.8] [release-4.9] Bug 2016275: [on-prem] Set coredns bufsize to 512

In response to this:

[release-4.8] [release-4.9] Bug 2009210: [on-prem] Set coredns bufsize to 512

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

@openshift-ci openshift-ci bot changed the title [release-4.8] [release-4.9] Bug 2009210: [on-prem] Set coredns bufsize to 512 [release-4.8] [release-4.9] Bug 2016275: [on-prem] Set coredns bufsize to 512 Oct 21, 2021
@openshift-ci openshift-ci bot added the bugzilla/severity-high Referenced Bugzilla bug's severity is high for the branch this PR is targeting. label Oct 21, 2021
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openshift-ci bot commented Oct 21, 2021

@openshift-cherrypick-robot: This pull request references Bugzilla bug 2016275, which is invalid:

  • expected dependent Bugzilla bug 2009210 to be in one of the following states: VERIFIED, RELEASE_PENDING, CLOSED (ERRATA), CLOSED (CURRENTRELEASE), but it is ON_QA instead

Comment /bugzilla refresh to re-evaluate validity if changes to the Bugzilla bug are made, or edit the title of this pull request to link to a different bug.

In response to this:

[release-4.8] [release-4.9] Bug 2016275: [on-prem] Set coredns bufsize to 512

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

@openshift-ci openshift-ci bot added the bugzilla/invalid-bug Indicates that a referenced Bugzilla bug is invalid for the branch this PR is targeting. label Oct 21, 2021
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mandre commented Oct 21, 2021

/retitle [release-4.8] Bug 2016275: [on-prem] Set coredns bufsize to 512

@openshift-ci openshift-ci bot changed the title [release-4.8] [release-4.9] Bug 2016275: [on-prem] Set coredns bufsize to 512 [release-4.8] Bug 2016275: [on-prem] Set coredns bufsize to 512 Oct 21, 2021
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mandre commented Oct 21, 2021

/retest-required

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openshift-ci bot commented Oct 21, 2021 •
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@openshift-cherrypick-robot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name Commit Details Required Rerun command
ci/prow/e2e-metal-assisted dd420c0 link false /test e2e-metal-assisted
ci/prow/okd-e2e-aws dd420c0 link false /test okd-e2e-aws
ci/prow/e2e-metal-ipi-ovn-dualstack dd420c0 link false /test e2e-metal-ipi-ovn-dualstack
ci/prow/okd-e2e-upgrade dd420c0 link false /test okd-e2e-upgrade

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@iamemilio @adduarte PTAL

@openshift-ci openshift-ci bot added the approved Indicates a PR has been approved by an approver from all required OWNERS files. label Oct 21, 2021
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/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: EmilienM, kikisdeliveryservice, openshift-cherrypick-robot

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@mrunalp mrunalp added the cherry-pick-approved Indicates a cherry-pick PR into a release branch has been approved by the release branch manager. label Oct 26, 2021
@openshift-merge-robot openshift-merge-robot merged commit 3b46a22 into openshift:release-4.8 Oct 26, 2021
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openshift-ci bot commented Oct 26, 2021

@openshift-cherrypick-robot: All pull requests linked via external trackers have merged:

Bugzilla bug 2016275 has been moved to the MODIFIED state.

In response to this:

[release-4.8] Bug 2016275: [on-prem] Set coredns bufsize to 512

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

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@kikisdeliveryservice kikisdeliveryservice kikisdeliveryservice approved these changes

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