Drop support for RHEL 7 / CentOS 7

[VannTen]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
This removes support for CentOS 7 and RHEL 7 (and derivatives)
Both are EOL in 1 mont (30/06/2024), though RHEL 7 will still have Extended Life Support, but this is quite limited support

This should reduce the complexity of some roles and will help with future development (for instance #11158 and #10701)

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

action required: RHEL 7, Centos 7 and derivatives are no longer supported.

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[yankay]

HI @VannTen

Although Centos 7 will be EOL on 2024-06-30, Centos 8 has EOL on 2021-12-31. 🤣
From: https://en.wikipedia.org/wiki/CentOS#Versioning_and_releases.

Centos 7 is the last version of Centos's Long-Life Cycle maintenance version. Although there are some options to replace it, many users still use Centos 7, which is still widely used.

Data of Cento's market share(I cannot find the accurate statistics for Centos 7):

So, a good strategy for Kubespray is to give Centos7 users time to change the OS. I can also help maintain the Centos 7 part of Kubespray. We can decide to drop the support of Cenots7 in 2025.

What do you think about that? :-)

[VannTen]

On Wed, May 29, 2024 at 06:49:47PM -0700, Kay Yan wrote: HI @VannTen Although Centos 7 will be EOL on 2024-06-30, Centos 8 has EOL on 2021-12-31. 🤣 From: https://en.wikipedia.org/wiki/CentOS#Versioning_and_releases.

Well, we can drop it as well, then. Though I think RHEL 8 probably share some stuff with CentOS 8, so it's probably not going to be as much of a gain.

So, a good strategy for Kubespray is to give Centos7 users time to change the OS. I can also help maintain the Centos 7 part of Kubespray. We can decide to drop the support of Cenots7 in 2025.

I'm strongly against maintaining support for OS past their own EOL. Users don't have to switch right away, only before upgrading to 2.26. Besides, if we were to push until 2025, what date would we choose ? 30-06-2024 being the official EOL for CentOS 7 and RHEL 7 makes it a natural switch point, IMO Not that this is not just to drop support for the sake of dropping support, it imposes a signifiant cost on new development as mentioned in the PR description.

[yankay]

There is a discuss in k/k, ref: kubernetes/kubernetes#116799.