Obtain gnu.org sources from mirrors
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# Problem Statement
As part of DRI duties I had seen quite some pipelines failing because
- [example 1](https://gitlab.com/gitlab-org/build/CNG/-/jobs/11961447065#L230)
- [example 2](https://dev.gitlab.org/gitlab/charts/components/images/-/jobs/31762084#L813)
- [example 3](https://dev.gitlab.org/gitlab/charts/components/images/-/jobs/31762084#L806)
I saw this problem across the CNG, charts and omnibus packages. I also have it locally. We are always referencing ftp.gnu.org but we should try to use mirrors to obtain the software we need.
# Goal
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Reduce the number of pipeline failures caused by ftp.gnu.org downtime.
- [ ] Replace ftp.gnu.org references with ftpmirror.gnu.org in CNG
- [ ] Replace ftp.gnu.org references with ftpmirror.gnu.org in [charts](https://dev.gitlab.org/gitlab/charts/components/images/-/issues/1)
- [ ] Replace ftp.gnu.org references with ftpmirror.gnu.org in omnibus
# DRI
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@sconstantingl
# Participants
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