Use ssh-ng by default

[matthewbauer]

I think this is now safe to do. I haven’t had any issues using ssh-ng, but I suspect most users don’t know
about it.

Relates to #4665

[Mic92]

Is there any writeup about what the difference between the two is? Do we get a changelog entry for this?

[Mic92]

cc @rickynils since this is a breaking change for nixbuild.net I believe.

[rickynils]

@Mic92 This shouldn't be breaking for nixbuild.net, since most of documentation for nixbuild.net explicitly states that you should use ssh://eu.nixbuild.net. So as long as the legacy remote builders still are supported, things should be fine for nixbuild.net. I do however intend to support ssh-ng too, since I want nixbuild.net to be completely interchangeable with a "normal" remote builder.

I would also be interested in some comparison between ssh:// and ssh-ng://, although I guess I'll notice the differences when implementing this for nixbuild.net.

[thufschmitt]

One thing that I think ssh:// does but not ssh-ng:// is respect the builders-use-substitutes flag (I didn’t try it recently, but https://github.com/NixOS/nix/blob/master/src/libstore/remote-store.cc#L291-L308 is ignoring the flag)

[Ericson2314]

I tried to beef up #4665 to account for this, and potential blockers like what the @regnat mentioned.

[rickynils]

nixbuild.net now supports ssh-ng:// in addition to ssh://, but it is not documented yet since we want to test it more.

[nyabinary]

Any reason why this hasn't been set to default yet?

[kjeremy]

I've been using this for a few years now. The only thing that I have run into is that ssh-ng stores do not work with nix log.

[Mic92]

@Enzime knows about a reason: nix-community/nixos-anywhere#366

[Mic92]

Basically this issue: #7359

[Enzime]

Not sure if this has been fixed yet #6950

[Ericson2314]

I would like to try doing this. (Another alternative is simply forcing the user to be explicit.)