Disable MPTCP by default

[rtribotte]

What does this PR do?

This PR disables MPTCP by default, which has been activated by default by the recent bump to go1.24.
MPTCP is now only enabled with GODEBUG=multipath=1.

Motivation

It appears that enabling MPTCP on some platforms can cause Traefik to stop with the following error logs message:

set tcp X.X.X.X:X->X.X.X.X:X: setsockopt: operation not supported

Disabling it by default solves this issue.

Fixes #11869

More

• Added/updated tests
• Added/updated documentation

Additional Notes

Co-authored-by: Kevin Pollet pollet.kevin@gmail.com

[nmengin]

LGTM

[dtscd]

I'm not opposed to this PR, but I would note that the fundamental problem, a single connection failed syscall to set the keepalive will crash the entire internal endpoint completely transparently (except for a log message). The dashboard will still appear as though the endpoint is up, even though the endpoint server is down, but the larger point of the syscall for setting keepalive should perhaps not stop the endpoint.

[nmengin]

Hello @dtscd,

Thank you for your feedback.
We've implemented this fix to address the issue in the short term.

We’ve also discussed making broader improvements to the socket creation options as a potential long-term solution, though it’s still in the planning phase.

[lbenguigui]

LGTM

[YuryHrytsuk]

@rtribotte thanks for this fix.

This PR is merged into 2.X branch (version) but it closes an issue created for traefik version 3.X.

Isn't it wrong? I have this #11869 in traefik version 3.4.4 and I don't know how to get rid of it (version 3.5.X does not mention your fix)

[YuryHrytsuk]

@rtribotte thanks for this fix.

This PR is merged into 2.X branch (version) but it closes an issue created for traefik version 3.X.

Isn't it wrong? I have this #11869 in traefik version 3.4.4 and I don't know how to get rid of it (version 3.5.X does not mention your fix)

Ah, I just realised, that 2.X branch was merged into 3.X branch and thus the fix was also moved to 3.X.

https://github.com/traefik/traefik/releases/tag/v3.4.5