what's exactly needed?

I'm not sure, but the error message I'm seeing comes from here:
https://github.com/golang/build/blob/7858236789478677d65917de2425af562568774a/cmd/coordinator/remote.go#L650-L663

It appears to need SSH public-key authentication for some user (typically either gopher or root), with the username configured in golang.org/x/build/dashboard/builders.go. I assume @andybons can get you the public key.

Or, if you'd prefer to diagnose #38797 yourself, that would work too. 😉

If you provide the public key I can add it to the root user.

@tuxillo is there a builder key present on the host per step 1 of https://github.com/golang/go/wiki/DashboardBuilders#how-to-set-up-a-builder ? (don’t paste it here)

Yes, sure. Otherwise it would not even connect as far as I can tell:

# ls -l ~/.gobuildkey-host-dragonfly-amd64-5_8
-rw-r--r--  1 root  wheel  33 Apr 14 16:37 /root/.gobuildkey-host-dragonfly-amd64-5_8

what's exactly needed?

The host config for the dragonfly-amd64-5_8 builder has the empty string value for the SSHUsername field in the golang.org/x/build/dashboard package:

https://github.com/golang/build/blob/916311cec4e1738aae572fe49767cebdc0351144/dashboard/builders.go#L363-L369

The empty string means "disable SSH access on this builder".

It needs to be set to a non-empty value, then coordinator needs to be redeployed. (Maybe more will need to be done afterwards.)

@tuxillo Could you please send a CL that updates the SSHUsername field in the x/build/dashboard package and add me as a reviewer? Thank you.

/cc @bradfitz Do you know if there are any tasks to do on the side of the reverse builder (by the builder owner) when enabling SSH access?

The buildlet binary is responsible for editing the authorized_keys file on the host. Finding the path to the appropriate file has needed some tweaks for different OSes over time. It's likely to work automatically on DragonFly at this point but if not, that's the place to look.

Thanks Brad.

@tuxillo If it's helpful to you, I can create the CL and make you a reviewer, but you'll need to tell me what username I should specify for your builder. Let me know how you'd like to proceed. Thanks.

IIRC it needs to be the user that runs the builder. The main reason it's not automatic is that some builder owners don't want to permit SSH into their network.

The DragonFly builders run in VMs so the user will be root.

@dmitshur I'll create the PR.

Change https://golang.org/cl/232337 mentions this issue: dashboard: enable SSH access in DragonFly BSD builders

Let me know if anything else is needed on my side.

Will do, thanks. Re-opening to track coordinator deployment.

Coordinator is re-deployed, and I've verified that it's possible to ssh into a dragonfly-amd64-5_8 gomote instance now. /cc @bcmills