Remove trust-ad from options line in /etc/resolv.conf
#440
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Prometheus stopped working for us, with panics that look like this:
panic: runtime error: slice bounds out of range [:9] with length 8
goroutine 425 [running]:
github.com/miekg/dns.ClientConfigFromReader(0x1b914a0, 0xc051786b38, 0x0, 0xc000000000, 0xc051786b38)
github.com/miekg/dns/clientconfig.go:94 +0x8d1
github.com/miekg/dns.ClientConfigFromFile(0x1900ba4, 0x10, 0x0, 0x0, 0x0)
github.com/miekg/dns/clientconfig.go:29 +0xde
github.com/prometheus/prometheus/discovery/dns.lookupWithSearchPath(0xc050c8ccf0, 0x2e, 0xc0518d0001, 0x1b8f4c0, 0xc0515a1e00, 0xc051873758, 0xc00041e678, 0x7b30d0)
github.com/prometheus/prometheus/discovery/dns/dns.go:245 +0x48
github.com/prometheus/prometheus/discovery/dns.(*Discovery).refreshOne(0xc0513c91d0, 0x1bb6140, 0xc0000d3a80, 0xc050c8ccf0, 0x2e, 0xc0519304e0, 0x26ed320, 0x164a5e0)
github.com/prometheus/prometheus/discovery/dns/dns.go:173 +0x77
github.com/prometheus/prometheus/discovery/dns.(*Discovery).refresh.func1(0xc0513c91d0, 0x1bb6140, 0xc0000d3a80, 0xc0519304e0, 0xc0516c9250, 0xc050c8ccf0, 0x2e)
github.com/prometheus/prometheus/discovery/dns/dns.go:154 +0x81
created by github.com/prometheus/prometheus/discovery/dns.(*Discovery).refresh
github.com/prometheus/prometheus/discovery/dns/dns.go:153 +0x175
This looked like it was barfing on the `options` line in
/etc/resolv.conf, on a string of length 8.
In June, a change was made to systemd-resolved to change the options
line from `options edns0` to `options edns0 trust-ad`. It looks like
this change is causing the panic in the miekd/dns library.
This change removes `trust-ad` from the `options` line because a) we
don't care about DNSSEC, and b) we think it's breaking things.
Note that systemd-resolved automatically determines whether it should
manage /etc/resolv.conf or not based on whether it is a symlink and
whether it includes 127.0.0.53 as a nameserver. So we think that
replacing the symlink will Do The Right Thing. We tested by manually
changing /etc/resolv.conf on a machine and rebooting it to see if it
still worked, and it did.
See https://jlk.fjfi.cvut.cz/arch/manpages/man/systemd-resolved.8#/ETC/RESOLV.CONF
> Note that the selected mode of operation for this file is detected
> fully automatically, depending on whether /etc/resolv.conf is a
> symlink to /run/systemd/resolve/resolv.conf or lists 127.0.0.53 as
> DNS server.
Co-authored-by: chrisfarms <chris.farmiloe@digital.cabinet-office.gov.uk>
Co-authored-by: Robert Scott <robert.scott@digital.cabinet-office.gov.uk>
risicle
approved these changes
Nov 16, 2020
cbaines
added a commit
to alphagov/tech-ops
that referenced
this pull request
Nov 18, 2020
This uses the same approach as taken for the Observe Prometheus [1]. The issue has been fixed in the upstream library [2] and the fix was released in version 1.0.5, but the current Ubuntu package is built with 1.0.4. 1: alphagov/prometheus-aws-configuration-beta#440 2: miekg/dns#642
risicle
added a commit
to alphagov/verify-infrastructure
that referenced
this pull request
May 4, 2021
to prevent prometheus from choking in a similar manner to alphagov/prometheus-aws-configuration-beta#440
risicle
added a commit
to alphagov/verify-infrastructure
that referenced
this pull request
May 4, 2021
to prevent prometheus from choking in a similar manner to alphagov/prometheus-aws-configuration-beta#440
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Prometheus stopped working for us, with panics that look like this:
This looked like it was barfing on the
optionsline in/etc/resolv.conf, on a string of length 8.
In June, a change was made to systemd-resolved to change the options
line from
options edns0tooptions edns0 trust-ad. It looks likethis change is causing the panic in the miekd/dns library.
This change removes
trust-adfrom theoptionsline because a) wedon't care about DNSSEC, and b) we think it's breaking things.
Note that systemd-resolved automatically determines whether it should
manage /etc/resolv.conf or not based on whether it is a symlink and
whether it includes 127.0.0.53 as a nameserver. So we think that
replacing the symlink will Do The Right Thing. We tested by manually
changing /etc/resolv.conf on a machine and rebooting it to see if it
still worked, and it did.
See https://jlk.fjfi.cvut.cz/arch/manpages/man/systemd-resolved.8#/ETC/RESOLV.CONF
Co-authored-by: chrisfarms chris.farmiloe@digital.cabinet-office.gov.uk
Co-authored-by: Robert Scott robert.scott@digital.cabinet-office.gov.uk