enabling ca-derivations makes deployments freeze

[sbourdeauducq]

1. Deploy a NixOS 22.05 system with nixops 2.0.0 and experimental-features = ca-derivations in the target machine's Nix configuration.
2. Deployment succeeds, target machine is now running with ca-derivations.
3. Run the deployment again. This time, it eventually prints:

machine......> waiting for exclusive access to the Nix store for ca drvs...

and freezes there, breaking all further deployments.

[roberth]

This looks like a Nix version compatibility bug.

@sbourdeauducq Which Nix version is on the machine and which Nix version do you run on the nixops side?

@Ericson2314 any ideas?

[sbourdeauducq]

2.8.1 on the machine and 2.4 on the nixops side.

[sbourdeauducq]

The bug is still the same after updating the nixops side to Nix 2.8.1.