deploy_nixos/nixos-deploy.sh: fix ControlPersist timeout

[betaboon]

fixes #20 by gracefully closing the multiplexing master process gracefully.

https://man.openbsd.org/ssh
Control an active connection multiplexing master process. When the -O option is specified, the ctl_cmd argument is interpreted and passed to the master process. Valid commands are: “check” (check that the master process is running), “forward” (request forwardings without command execution), “cancel” (cancel forwardings), “exit” (request the master to exit), and “stop” (request the master to stop accepting further multiplexing requests).

[zimbatm]

@betaboon: what problem does it solve? Persisted connections should automatically timeout and be discarded in the background.

[betaboon]

@zimbatm as mentioned in #20 the persisted connection only times out N-seconds after it has been active last. thus it takes N second for the deployment to finish even after it is actually done.

[zimbatm]

What I don't understand is why this is blocking the script in the first place. My understanding is that the TCP connection is maintained in the background somehow and shouldn't prevent the script from exiting.

[betaboon]

i wonder if this is related:
hashicorp/terraform#12139
hashicorp/terraform#22037

[zimbatm]

@betaboon I pushed another version that also cleans-up on unhappy paths. Since the ControlPath is now specific to this script I also moved it to be a temp file to avoid clashes with other potentially-running scripts.

[betaboon]

@zimbatm nice improvements. just checked them out and tested them with my setup. seems to work as expected :)

[zimbatm]

thanks!

[betaboon]

thank you very much

[Profpatsch]

Thanks, I just tried it out in our deployment and it works.